Samacheer Kalvi Class 11 Chemistry Solutions Chapter 5 Alkali and Alkaline Earth Metals

Textual Questions:

I. Choose the Best Answer:

 

Question 1. For alkali metals, which one of the following trends is incorrect?
(a) Hydration energy: Li > Na > K> Rb
(b) Ionisation energy: Li> Na> K> Rb
(c) Density: Li < Na < K < Rb
(d) Atomic size: Li < Na < K < Rb
Answer: (c) Density: Li < Na < K < Rb
In simple words: Among alkali metals, lithium has the lowest density. As you go down the group (Li to Rb), density generally increases because the atoms get heavier.

🎯 Exam Tip: Remember the general trends of properties down a group in the periodic table. Density often increases with atomic mass for elements in the same group, though some exceptions might exist.

 

Question 2. Which of the following statements is incorrect?
(a) Li\(^{+}\) has minimum degree of hydration among alkali metal cations
(b) The oxidation state of K in KO\(_{2}\) is +1
(c) Sodium is used to make Na / Pb alloy
(d) MgSO\(_{4}\) is readily soluble in water
Answer: (a) Li\(^{+}\) has minimum degree of hydration among alkali metal cations
In simple words: The statement is wrong because lithium ions (Li\(^{+}\)) are actually the most hydrated among alkali metal cations due to their small size. Small ions attract more water molecules.

🎯 Exam Tip: Hydration energy is inversely proportional to the size of the ion. Smaller ions have a higher charge density, leading to stronger attraction for water molecules and thus higher hydration energy.

 

Question 3. Which of the following compounds will not evolve H\(_{2}\) gas on reaction with alkali metals?
(a) ethanoic acid
(b) ethanol
(c) phenol
(d) none of these
Answer: (d) none of these
In simple words: All the given options - ethanoic acid, ethanol, and phenol - contain acidic hydrogen atoms. These acidic hydrogens will react with highly reactive alkali metals to produce hydrogen gas.

🎯 Exam Tip: Alkali metals are very reactive and can react with compounds containing even weakly acidic hydrogen (like -OH or -COOH groups) to release hydrogen gas. Test for the presence of such groups.

 

Question 4. Which of the following has the highest tendency to give the reaction, M\(^{+}\)(g) \( \xrightarrow{ \text{Aqueous Medium} } \) M\(^{+}\)(aq)
(a) Na
(b) Li
(c) Rb
(d) K
Answer: (b) Li
In simple words: Lithium has the strongest tendency to form aqueous ions from gaseous ions. This is because lithium ions are very small, so they attract many water molecules around them, releasing a lot of energy.

🎯 Exam Tip: The hydration enthalpy (energy released when gaseous ions dissolve in water) is highest for smaller ions because they have a higher charge density and attract water molecules more strongly. This strong hydration makes them stable in aqueous solution.

 

Question 5. sodium is stored in
(a) alcohol
(b) water
(c) kerosene
(d) none of these
Answer: (c) kerosene
In simple words: Sodium is a very reactive metal that reacts quickly with air and water. Storing it in kerosene keeps it away from air and moisture, preventing dangerous reactions.

🎯 Exam Tip: Remember that alkali metals are highly reactive and must be stored under inert conditions. Kerosene is a common choice because it doesn't react with the metal and keeps it isolated from the environment.

 

Question 6. RbO\(_{2}\) is
(a) superoxide and paramagnetic
(b) peroxide and diamagnetic
(c) superoxide and diamagnetic
(d) peroxide and paramagnetic
Answer: (a) superoxide and paramagnetic
In simple words: Rubidium forms a superoxide (RbO\(_{2}\)), which means it has an O\(_{2}^{-}\) ion. This ion has an unpaired electron, making the compound attracted to a magnetic field.

🎯 Exam Tip: Recall that alkali metals react with oxygen to form different types of oxides: monoxides (Li, Na), peroxides (Na), and superoxides (K, Rb, Cs). Superoxides contain the O\(_{2}^{-}\) ion, which is paramagnetic due to an unpaired electron.

 

Question 7. Find the wrong statement
(a) sodium metal is used in organic qualitative analysis
(b) sodium carbonate is soluble in water and it is used in inorganic qualitative analysis
(c) potassium carbonate can be prepared by solvay process
(d) potassium bicarbonate is acidic salt
Answer: (c) potassium carbonate can be prepared by solvay process
In simple words: The Solvay process is used to make sodium carbonate, not potassium carbonate. Potassium bicarbonate is too soluble to precipitate, which is why the Solvay process doesn't work for potassium.

🎯 Exam Tip: Understand the limitations of industrial processes. The Solvay process relies on the low solubility of sodium bicarbonate, a condition not met by potassium bicarbonate, making it unsuitable for potassium carbonate production.

 

Question 8. Lithium shows diagonal relationship with
(a) sodium
(b) magnesium
(c) calcium
(d) aluminium
Answer: (b) magnesium
In simple words: Lithium and magnesium share similar properties because they are diagonally placed in the periodic table. This happens because their size and electronegativity values are quite similar.

🎯 Exam Tip: The diagonal relationship occurs between elements of period 2 and period 3, diagonally opposite to each other. It's important to remember these specific pairs, such as Li-Mg, Be-Al, and B-Si.

 

Question 9. Incase of alkali metal halides, the ionic character increases in the order
(a) MF < MCI < MBr < MI
(b) MI < MBr < MCI < MF
(c) MI < MBr < MF < MCI
(d) none of these
Answer: (b) MI < MBr < MCI < MF
In simple words: The smallest halide ion (fluoride, F) has the strongest attraction to the metal, making its bond most ionic. As the halide ion gets bigger (like iodide, I), it becomes easier for the metal to pull its electrons, making the bond less ionic and more covalent.

🎯 Exam Tip: Ionic character increases with decreasing polarizing power of the cation and increasing polarizability of the anion. For a given cation M\(^{+}\), the smaller the anion, the more ionic the bond. Therefore, MF (M\(^{+}\)F\(^{-}\)) is the most ionic and MI (M\(^{+}\)I\(^{-}\)) is the least ionic.

 

Question 10. In which process, fused sodium hydroxide is electrolysed for extraction of sodium?
(a) Castner's process
(b) Cyanide process
(c) Down process
(d) All of these
Answer: (a) Castner's process
In simple words: The Castner's process is a method specifically designed to extract sodium metal using electrolysis of melted sodium hydroxide. It's a key industrial method for getting pure sodium.

🎯 Exam Tip: Familiarize yourself with common industrial processes for metal extraction. The Down's process, for instance, is another important method but uses molten NaCl, not NaOH.

 

Question 11. The product obtained as a result of a reaction of nitrogen with CaC\(_{2}\) is
(a) Ca(CN)\(_{3}\)
(b) CaN\(_{2}\)
(c) Ca(CN)\(_{2}\)
(d) Ca\(_{3}\)N\(_{2}\)
Answer: (c) Ca(CN)\(_{2}\)
In simple words: When calcium carbide reacts with nitrogen, it forms calcium cyanamide, which has the chemical formula Ca(CN)\(_{2}\). This is a known chemical reaction used in industry.

🎯 Exam Tip: Remember specific reactions, especially those involving carbides and nitrogen, as they often form industrially important compounds like cyanamides.

 

Question 12. Which of the following has highest hydration energy
(a) MgCl\(_{2}\)
(b) CaCl\(_{2}\)
(c) BaCl\(_{2}\)
(d) SrCl\(_{2}\)
Answer: (a) MgCl\(_{2}\)
In simple words: Magnesium chloride has the highest hydration energy because the magnesium ion (Mg\(^{2+}\)) is the smallest among the options. Smaller ions attract water molecules more strongly.

🎯 Exam Tip: Hydration energy is inversely proportional to the ionic radius. Among ions with the same charge, the smallest ion will have the highest hydration energy.

 

Question 13. Match the flame colours of the alkali and alkaline earth metal salts in the bunsen burner

(a) p - 2, q - 1, r - 4, s - 5, t - 6, u - 3
(b) p - 1, q - 2, r - 4, s - 5, t - 6, u - 3
(c) p - 4, q - 1, r - 2, s - 3, t - 5, u - 6
(d) p - 6, q - 5, r - 4, s - 3, t - 1, u - 2
Answer: (a) p - 2, q - 1, r - 4, s - 5, t - 6, u - 3
In simple words: Different metal salts give off unique colors when heated in a flame. This property helps us identify them. For example, sodium gives yellow, calcium gives brick red, and so on.

🎯 Exam Tip: Memorizing the characteristic flame colors for common alkali and alkaline earth metals is essential for qualitative analysis in chemistry. It's a reliable way to identify these elements.

 

Question 14. Assertion: Generally alkali and alkaline earth metals form superoxides Reason: There is a single bond between O and O in superoxides.
(a) both assertion and reason are true and reason is the correct explanation of assertion.
(b) both assertion and reason are true but reason is not the correct explanation of assertion
(c) assertion is true but reason is false
(d) both assertion and reason are false
Answer: (d) both assertion and reason are false
In simple words: Both statements are incorrect. Only heavier alkali metals form superoxides. The oxygen molecule in superoxide has a single covalent bond and a three-electron bond.

🎯 Exam Tip: Pay close attention to exceptions and specific conditions. Not all alkali or alkaline earth metals form superoxides; this is typically observed for larger, more electropositive elements like K, Rb, and Cs due to their ability to stabilize the large superoxide ion.

 

Question 15. Assertion: BeSO\(_{4}\) is soluble in water while BaSO\(_{4}\) is not Reason: Hydration energy decreases down the group from Be to Ba and lattice energy remains almost constant.
(a) both assertion and reason are true and reason is the correct explanation of assertion
(b) both assertion and reason are true but reason is not the correct explanation of assertion
(c) assertion is true but reason is false
(d) both assertion and reason are false
Answer: (a) both assertion and reason are true and reason is the correct explanation of assertion
In simple words: Beryllium sulfate dissolves in water because the small Be\(^{2+}\) ion attracts water strongly, releasing enough energy to break the bonds in the solid. Barium sulfate does not dissolve because its larger Ba\(^{2+}\) ion does not attract water as strongly.

🎯 Exam Tip: Solubility of ionic compounds often depends on the balance between lattice energy (energy holding the solid together) and hydration energy (energy released when ions dissolve). For sulfates, as you go down the group, hydration energy drops faster than lattice energy, making lower sulfates less soluble.

 

Question 16. Which is the correct sequence of solubility of carbonates of alkaline earth metals?
(a) BaCO\(_{3}\) > SrCO\(_{3}\) > CaCO\(_{3}\) > MgCO\(_{3}\)
(b) MgCO\(_{3}\) > CaCO\(_{3}\) > SrCO\(_{3}\) > BaCO\(_{3}\)
(c) CaCO\(_{3}\) > BaCO\(_{3}\) > SrCO\(_{3}\) > MgCO\(_{3}\)
(d) BaCO\(_{3}\) > CaCO\(_{3}\) > SrCO\(_{3}\) > MgCO\(_{3}\)
Answer: (b) MgCO\(_{3}\) > CaCO\(_{3}\) > SrCO\(_{3}\) > BaCO\(_{3}\)
In simple words: The carbonates of alkaline earth metals become less soluble as you move down the group. This means magnesium carbonate is the most soluble, and barium carbonate is the least soluble.

🎯 Exam Tip: For alkaline earth metal carbonates, the decrease in hydration energy down the group is more significant than the decrease in lattice energy, leading to a decrease in solubility from Mg to Ba.

 

Question 17. In context with beryllium, which one of the following statements is incorrect?
(a) It is rendered passive by nitric acid
(b) It forms Be\(_{2}\)C
(c) Its salts are rarely hydrolysed
(d) Its hydride is electron deficient and polymeric
Answer: (c) Its salts are rarely hydrolysed
In simple words: Beryllium salts actually undergo hydrolysis quite easily because the small, highly charged beryllium ion attracts water molecules strongly. So, the statement that they are rarely hydrolyzed is incorrect.

🎯 Exam Tip: Small, highly charged cations like Be\(^{2+}\) have a strong polarizing power, which makes their salts prone to hydrolysis in water, producing acidic solutions. This is a key characteristic of beryllium chemistry.

 

Question 18. The suspension of slaked lime in water is known as
(a) lime water
(b) quick lime
(c) milk of lime
(d) aqueous solution of slaked lime
Answer: (c) milk of lime
In simple words: When slaked lime (calcium hydroxide) is mixed with water, it forms a thick, milky mixture called milk of lime. This is different from lime water, which is a clear solution.

🎯 Exam Tip: Be precise with chemical terminology. "Lime water" is a clear solution of calcium hydroxide, while "milk of lime" is a suspension, meaning solid particles are dispersed in water, making it opaque.

 

Question 19. A colourless solid substance (A) on heating evolved CO\(_{2}\) and also gave a white residue, soluble in water. Residue also gave CO\(_{2}\) when treated with dilute HCl.
(a) Na\(_{2}\)CO\(_{3}\)
(b) NaHCO\(_{3}\)
(c) CaCO\(_{3}\)
(d) Ca(HCO\(_{3}\))\(_{2}\)
Answer: (b) NaHCO\(_{3}\)
In simple words: Sodium bicarbonate (A) breaks down when heated, releasing carbon dioxide gas and leaving sodium carbonate as a solid. This solid then reacts with acid to release more carbon dioxide.

🎯 Exam Tip: This question tests your knowledge of the thermal decomposition of bicarbonates and the reaction of carbonates with acids. Sodium bicarbonate is a key compound that fits this reaction pattern perfectly.

 

Question 20. The compound (X) on heating gives a colourless gas and a residue that is dissolved in water to obtain (B). Excess of CO\(_{2}\) is bubbled through aqueous solution of B, C is formed. Solid (C) on heating gives back X. (B) is
(a) CaCO\(_{3}\)
(b) Ca(OH)\(_{2}\)
(c) Na\(_{2}\)CO\(_{3}\)
(d) NaHCO\(_{3}\)
Answer: (b) Ca(OH)\(_{2}\)
In simple words: The compound B must be calcium hydroxide. This substance is formed when the residue from heating X dissolves in water, and it is a key part of the reactions involving calcium carbonate, carbon dioxide, and water.

🎯 Exam Tip: This is a chain reaction problem. Breaking down each step (heating, dissolving, reacting with CO2, then heating again) helps identify the compounds. Recognizing that C gives back X means C is an intermediate form of X, often a bicarbonate from a carbonate.

 

Question 21. Which of the following statement is false?
(a) Ca\(^{2+}\) ions are not important in maintaining the regular beating of the heart
(b) Mg\(^{2+}\) ions are important in the green parts of the plants
(c) Mg\(^{2+}\) ions form a complex with ATP
(d) Ca\(^{2+}\) ions are important in blood clotting
Answer: (a) Ca\(^{2+}\) ions are not important in maintaining the regular beating of the heart
In simple words: The statement is false because calcium ions (Ca\(^{2+}\)) are actually very important for the heart to beat normally and for muscle contractions in the body. They play a vital role.

🎯 Exam Tip: Recall the biological roles of common ions. Calcium ions are critical for many bodily functions, including muscle contraction, nerve impulse transmission, and blood clotting, in addition to bone formation.

 

Question 22. The name 'Blue John' is given to which of the following compounds?
(a) CaH\(_{2}\)
(b) CaF\(_{2}\)
(c) Ca\(_{3}\)(PO\(_{4}\))\(_{2}\)
(d) CaO
Answer: (b) CaF\(_{2}\)
In simple words: 'Blue John' is a common name for a rare blue-violet variety of calcium fluoride, which is a mineral called fluorite. It is used as an ornamental stone.

🎯 Exam Tip: Learn the common names of important minerals and compounds. 'Blue John' is a unique case where a specific colored variety of a common mineral has a special name, often linked to its historical use or appearance.

 

Question 23. Formula of Gypsum is
(a) CaSO\(_{4}\).2H\(_{2}\)O
(b) CaSO\(_{4}\).\( \frac{1}{2} \)H\(_{2}\)O
(c) 3CaSO\(_{4}\).H\(_{2}\)O
(d) 2CaSO\(_{4}\).2H\(_{2}\)O
Answer: (a) CaSO\(_{4}\).2H\(_{2}\)O
In simple words: Gypsum is a mineral made of calcium sulfate combined with two molecules of water. It is a very common compound used in construction and other industries.

🎯 Exam Tip: It is crucial to remember the chemical formulas of common compounds, especially those with water of crystallization, as they are fundamental to chemistry.

 

Question 24. When CaC\(_{2}\) is heated in atmospheric nitrogen in an electric furnace the compound formed is
(a) Ca(CN)\(_{2}\)
(b) CaNCN
(c) CaC\(_{2}\)N\(_{2}\)
(d) CaNC\(_{2}\)
Answer: (b) CaNCN
In simple words: When calcium carbide is heated with nitrogen, it produces calcium cyanamide, which can also be written as CaNCN. This compound is important in agriculture.

🎯 Exam Tip: Note that Ca(CN)\(_{2}\) and CaNCN are two common representations of calcium cyanamide. Both formulas are chemically equivalent and important to recognize for the reaction of calcium carbide with nitrogen.

 

Question 25. Among the following the least thermally stable is
(a) K\(_{2}\)CO\(_{3}\)
(b) Na\(_{2}\)CO\(_{3}\)
(c) BaCO\(_{3}\)
(d) Li\(_{2}\)CO\(_{3}\)
Answer: (d) Li\(_{2}\)CO\(_{3}\)
In simple words: Lithium carbonate is the least stable when heated because lithium's small size leads to stronger polarizing power. This makes the carbonate ion more likely to break down.

🎯 Exam Tip: Thermal stability of carbonates generally increases down a group for alkali and alkaline earth metals. Lithium carbonate is an exception among alkali metal carbonates due to the small size and high polarizing power of the Li\(^{+}\) ion, making it decompose at lower temperatures than other alkali metal carbonates.

II. Write Brief Answer to the Following Questions:

 

Question 26. Why sodium hydroxide is much more water-soluble than chloride?
Answer: Sodium hydroxide is much more soluble than sodium chloride because its ions, Na\(^{+}\) and OH\(^{-}\), are more attracted to water molecules. The hydroxide ion (OH\(^{-}\)) is smaller than the chloride ion (Cl\(^{-}\)) and can form stronger hydrogen bonds with water. This stronger interaction with water, called intense hydration, causes sodium hydroxide to dissolve easily and release a lot of heat. The attraction of the ions to water molecules is strong enough to overcome the forces holding them together in the solid.
In simple words: Sodium hydroxide dissolves better in water because its ions connect more strongly with water molecules than sodium chloride ions do. The small OH\(^{-}\) ion helps form strong bonds with water, pulling the compound apart easily.

🎯 Exam Tip: When comparing solubility, consider both the size of the ions and their ability to form hydrogen bonds with water. Smaller, highly charged ions and those capable of hydrogen bonding often lead to higher solubility due to greater hydration energy.

 

Question 27. Explain what to mean by efflorescence.
Answer: Efflorescence is a process where a crystalline hydrate (a compound with water molecules trapped in its structure) spontaneously loses its water of hydration to the atmosphere. This happens when the vapor pressure of the hydrate is higher than the atmospheric water vapor pressure. For example, sodium carbonate decahydrate, which is a white solid, loses water when heated, first forming a monohydrate (Na\(_{2}\)CO\(_{3}\).H\(_{2}\)O) and then becoming anhydrous sodium carbonate, also known as soda ash.
\( \text{Na}_{2}\text{CO}_{3}.10\text{H}_{2}\text{O} \rightarrow \text{Na}_{2}\text{CO}_{3}.\text{H}_{2}\text{O} + 9\text{H}_{2}\text{O} \)
\( \text{Na}_{2}\text{CO}_{3}.\text{H}_{2}\text{O} \rightarrow \text{Na}_{2}\text{CO}_{3} + \text{H}_{2}\text{O} \)
In simple words: Efflorescence is when a crystal loses its water to the air, becoming a powder. Think of it like a wet cloth drying out and leaving behind a solid.

🎯 Exam Tip: Understand the difference between efflorescence, deliquescence (absorbing moisture until a solution forms), and hygroscopy (absorbing moisture without forming a solution). These terms describe how compounds interact with atmospheric moisture.

 

Question 28. Write the chemical equations for the reactions involved in solvay process of preparation of sodium carbonate.
Answer: The Solvay process involves several key chemical reactions to produce sodium carbonate. First, ammonia reacts with water and carbon dioxide to form ammonium carbonate, which then further reacts to form ammonium bicarbonate. This ammonium bicarbonate then reacts with sodium chloride, precipitating out sodium bicarbonate due to its low solubility. Finally, the sodium bicarbonate is heated to yield sodium carbonate.
\( 2\text{NH}_{3} + \text{H}_{2}\text{O} + \text{CO}_{2} \rightarrow (\text{NH}_{4})_{2}\text{CO}_{3} \)
\( (\text{NH}_{4})_{2}\text{CO}_{3} + \text{H}_{2}\text{O} + \text{CO}_{2} \rightarrow 2\text{NH}_{4}\text{HCO}_{3} \)
\( 2\text{NH}_{4}\text{HCO}_{3} + \text{NaCl} \rightarrow \text{NH}_{4}\text{Cl} + \text{NaHCO}_{3} \)
\( 2\text{NaHCO}_{3} \rightarrow \text{Na}_{2}\text{CO}_{3} + \text{CO}_{2} + \text{H}_{2}\text{O} \)
In simple words: The Solvay process is like a step-by-step cooking recipe to make washing soda. It starts with ammonia, water, and carbon dioxide, leading to sodium bicarbonate, which is then heated to become sodium carbonate.

🎯 Exam Tip: For processes like Solvay, it's essential to not only know the overall reaction but also the balanced chemical equations for each intermediate step. This demonstrates a thorough understanding of the mechanism.

 

Question 29. An alkali metal (x) forms a hydrated sulphate, X\(_{2}\)SO\(_{4}\) .10H\(_{2}\)O. Is the metal more likely to be sodium (or) potassium?
Answer: The metal is more likely to be **sodium**. This is because sodium ions, being smaller than potassium ions, have a higher charge density. This means sodium ions attract water molecules more strongly, favoring the formation of stable hydrated salts like sodium sulfate decahydrate (Na\(_{2}\)SO\(_{4}\).10H\(_{2}\)O). Larger ions like potassium have less intense hydration.
In simple words: Sodium is a better fit because its ions are smaller and pull water to them more strongly. This helps it form a hydrated salt with ten water molecules, which potassium usually doesn't do.

🎯 Exam Tip: Remember that hydration tendency is inversely related to ionic size for a given charge. Smaller ions have higher charge density, leading to stronger interactions with water and greater hydration. This principle helps explain the formation of hydrated salts.

 

Question 30. Write a balanced chemical equation for each of the following chemical reactions.
(i) Lithium metal with nitrogen gas
(ii) heating solid sodium bicarbonate
(iii) Rubidium with oxygen gas
(iv) solid potassium hydroxide with CO\(_{2}\)
(v) heating calcium carbonate
(vi) heating calcium with oxygen
Answer: Here are the balanced chemical equations for each reaction, showing how different elements and compounds interact.
(i) \( 6\text{Li(s)} + \text{N}_{2}\text{(g)} \rightarrow 2\text{Li}_{3}\text{N(s)} \)
(ii) \( 2\text{NaHCO}_{3}\text{(s)} \rightarrow \text{Na}_{2}\text{CO}_{3}\text{(s)} + \text{CO}_{2}\text{(g)} + \text{H}_{2}\text{O(g)} \)
(iii) \( \text{Rb} + \text{O}_{2} \rightarrow \text{RbO}_{2} \)
(iv) \( 2\text{KOH} + \text{CO}_{2} \rightarrow \text{K}_{2}\text{CO}_{3} + \text{H}_{2}\text{O} \)
(v) \( \text{CaCO}_{3} \rightarrow \text{CaO} + \text{CO}_{2} \)
(vi) \( 2\text{Ca} + \text{O}_{2} \rightarrow 2\text{CaO} \)
In simple words: These equations show how different chemicals change when they react. For example, lithium reacts with nitrogen to make a compound, and heating baking soda breaks it into smaller pieces.

🎯 Exam Tip: Always ensure chemical equations are balanced, meaning the number of atoms of each element is the same on both sides of the arrow. This respects the law of conservation of mass.

 

Question 31. Discuss briefly the similarities between beryllium and aluminium.
Answer: Beryllium shows a diagonal relationship with aluminium, meaning they share several similar chemical properties despite being in different groups.
1. Both beryllium chloride (BeCl\(_{2}\)) and aluminium chloride (AlCl\(_{3}\)) form dimeric structures with chloride bridges, and also polymeric chain structures. Both are soluble in organic solvents and act as strong Lewis acids.
2. Beryllium hydroxide (Be(OH)\(_{2}\)) dissolves in excess alkali to form beryllate ion, \( [\text{Be(OH)}_{4}]^{2-} \), similar to how aluminium hydroxide forms aluminate ion, \( [\text{Al(OH)}_{4}]^{-} \).
3. Both beryllium and aluminium ions have a strong tendency to form complex ions, such as \( \text{BeF}_{4}^{2-} \) and \( \text{AlF}_{6}^{3-} \).
4. The hydroxides of both beryllium and aluminium are amphoteric, meaning they can react with both acids and bases.
5. Carbides of beryllium (Be\(_{2}\)C) and aluminium (Al\(_{4}\)C\(_{3}\)) both react with water (hydrolysis) to produce methane gas.
6. Both beryllium and aluminium are rendered passive (unreactive) when treated with nitric acid due to the formation of an oxide layer.
In simple words: Beryllium and aluminium are like chemical cousins, sharing many traits because of their similar size and charge properties. They form similar structures, react in similar ways, and even become unreactive with nitric acid.

🎯 Exam Tip: The diagonal relationship is a crucial concept. For Be and Al, remember their similar polarizing power (charge/radius ratio) leads to similar properties in compound formation, acidic/basic nature of oxides/hydroxides, and complex formation.

 

Question 32. Give the systematic names for the following
(i) milk of magnesia
(ii) lye
(iii) lime
(iv) Caustic potash
(v) washing soda
(vi) soda ash
(vii) trona
Answer: Here are the systematic chemical names for the given common substances.
(i) Magnesium hydroxide
(ii) Sodium hydroxide (also known as caustic soda)
(iii) Calcium oxide
(iv) Potassium hydroxide
(v) Sodium carbonate decahydrate
(vi) Sodium carbonate (anhydrous)
(vii) Sodium sesquicarbonate
In simple words: This lists the proper science names for everyday items like milk of magnesia (magnesium hydroxide) or washing soda (sodium carbonate).

🎯 Exam Tip: Knowing the common names along with their systematic chemical names and formulas is important. This helps in understanding chemical discussions and practical applications.

 

Question 33. Substantiate Lithium fluoride has the lowest solubility among group one metal fluorides.
Answer: Lithium fluoride (LiF) has the lowest solubility among the alkali metal fluorides because of the very high lattice enthalpy compared to its hydration enthalpy. Both Li\(^{+}\) and F\(^{-}\) ions are very small. This small size allows them to pack very closely together in the crystal lattice, leading to extremely strong electrostatic forces and a very high lattice enthalpy. The hydration enthalpy, while significant due to the small ions, is not enough to overcome this strong lattice energy, resulting in low solubility.
In simple words: Lithium fluoride doesn't dissolve well in water because its ions are tiny and stick together very, very strongly in the solid. Water can't pull them apart easily enough to dissolve them.

🎯 Exam Tip: The solubility of ionic compounds is a balance between lattice energy and hydration energy. For LiF, the exceptionally high lattice energy, due to the small size of both ions, is the dominant factor, leading to very low solubility.

 

Question 34. Mention the uses of plaster of paris.
Answer: Plaster of Paris is a versatile material with many uses across different fields.
1. In the building industry, it is widely used as plaster for walls and ceilings.
2. It is crucial in medicine for immobilizing fractured bones or sprains, forming casts that help bones heal properly.
3. Dentists use it to make dental casts and impressions.
4. It is also used in ornamental work, for creating decorative items, and for making molds for statues and busts.
In simple words: Plaster of Paris is used for many things, like finishing walls, making casts for broken bones, and creating models or decorations. It's a very helpful material.

🎯 Exam Tip: When listing uses of a substance, try to categorize them (e.g., medical, construction, artistic) to ensure a comprehensive answer and demonstrate broad knowledge.

 

Question 35. Beryllium halides are Covalent whereas magnesium halides are ionic why?
Answer: Beryllium halides are covalent, while magnesium halides are ionic, primarily due to the significant difference in their ionic sizes and electronegativities. Beryllium has a very small atomic size and high electronegativity compared to other alkaline earth metals. This makes the Be\(^{2+}\) ion highly polarizing, meaning it can distort the electron cloud of the halide ion very effectively, leading to a significant sharing of electrons and thus covalent character. Magnesium, being larger and less electronegative, forms Mg\(^{2+}\) ions that are less polarizing, favoring the formation of ionic bonds with halides.
In simple words: Beryllium halides are covalent because beryllium is tiny and pulls on electrons strongly, making it share electrons more. Magnesium is bigger and less strong, so it just gives away its electrons to form ionic bonds.

🎯 Exam Tip: This question relates to Fajan's rules, which explain the transition from ionic to covalent character. Remember that smaller, highly charged cations lead to greater covalent character, especially with larger anions.

 

Question 36. Alkaline earth metal (A), belongs to 3rd period reacts with oxygen and nitrogen to form compound (B) and (C) respectively. It undergoes metal displacement reaction with AgNO\(_{3}\) solution to form compound (D).
Answer: The alkaline earth metal (A) from the 3rd period is Magnesium (Mg).
It reacts with oxygen to form magnesium oxide (B), and with nitrogen to form magnesium nitride (C). It displaces silver from silver nitrate to form magnesium nitrate (D).
\( \text{A} = \text{Magnesium} (\text{Mg}) \)
\( 2\text{Mg} + \text{O}_{2} \rightarrow 2\text{MgO} \) (\text{B} = Magnesium oxide)
\( 3\text{Mg} + \text{N}_{2} \rightarrow \text{Mg}_{3}\text{N}_{2} \) (\text{C} = Magnesium nitride)
\( \text{Mg} + 2\text{AgNO}_{3} \rightarrow 2\text{Ag} + \text{Mg(NO}_{3})_{2} \) (\text{D} = Magnesium nitrate)
In simple words: The mystery metal is magnesium. It reacts with oxygen to make magnesium oxide and with nitrogen to make magnesium nitride. It also replaces silver in silver nitrate solution, forming magnesium nitrate.

🎯 Exam Tip: For problems involving unknown compounds, break down the clues: period number, reactions (with O2, N2), and type of reaction (metal displacement) to identify the elements and compounds step-by-step.

 

Question 37. Write balanced chemical equation for the following processes
(a) heating calcium in oxygen
(b) heating calcium carbonate
(c) evaporating a solution of calcium hydrogen carbonate
(d) heating calcium oxide with carbon
Answer:
(a) For heating calcium in oxygen: \( 2\text{Ca} + \text{O}_2 \rightarrow 2\text{CaO} \)
(b) For heating calcium carbonate: \( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \)
(c) For evaporating a solution of calcium hydrogen carbonate: \( \text{Ca}(\text{HCO}_3)_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{CaCO}_3 \)
(d) For heating calcium oxide with carbon: \( \text{CaO} + 3\text{C} \rightarrow \text{CaC}_2 + \text{CO} \)
In simple words: These equations show how different calcium compounds react when heated or combined with other elements. Each equation represents a chemical change where new substances are formed.

🎯 Exam Tip: Always balance the chemical equations correctly by ensuring the number of atoms for each element is the same on both sides of the reaction.

 

Question 38. Explain the important common features of Group 2 elements.
Answer:
1. Group 2 elements are known as alkaline earth metals. They are soft, silvery metals, but they are less metallic than Group 1 elements. The heavier metals like Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra) are nearly as reactive as alkali metals.
2. Their general electron configuration is written as \( [\text{Noble gas}]\text{ns}^2 \), where 'n' stands for the valence shell number. This means they have two electrons in their outermost shell.
In simple words: Group 2 elements are called alkaline earth metals. They are softer than other metals and have two electrons in their outer shell, making them able to form strong bonds.

🎯 Exam Tip: Remember that the number of valence electrons determines an element's group and often its main chemical properties.

 

Question 39. Discus the similarities between beryllium and aluminium.
Answer:
1. Beryllium chloride (BeCl\( _2 \)) forms a dimeric structure similar to aluminium chloride (AlCl\( _3 \)), with chlorine bridges. It can also form a chain-like polymeric structure. Both are easily dissolved in organic solvents and act as strong Lewis acids.
2. Beryllium hydroxide \( (\text{Be}(\text{OH})_2) \) dissolves when there is too much alkali, forming beryllate ion \( ([\text{Be}(\text{OH})_4]^{2-}) \). This is similar to how aluminium hydroxide \( (\text{Al}(\text{OH})_3) \) reacts to form aluminate ion \( ([\text{Al}(\text{OH})_4]^{-}) \).
3. Both beryllium and aluminium ions show a strong tendency to form complex compounds, such as \( \text{BeF}_4^{2-} \) and \( \text{AlF}_6^{3-} \). This property is common due to their small size and high charge density.
4. The hydroxides of both beryllium and aluminium are amphoteric. This means they can react as both an acid and a base. This flexibility is key to many of their chemical reactions.
In simple words: Beryllium and aluminium are alike because their chlorides form similar structures and dissolve in the same types of liquids. Their hydroxides also react in the same way, acting as both acids and bases.

🎯 Exam Tip: The diagonal relationship helps predict similar chemical properties between elements that are not in the same group, often due to similar charge density or electronegativity.

 

Question 40. Why alkaline earth metals are harder than alkali metals?
Answer: Alkaline earth metals are harder than alkali metals because they have a stronger metallic bond. This is due to the presence of two valence electrons in their outermost shell, compared to alkali metals which only have one valence electron. With more electrons available for metallic bonding, the attractive forces between the metal atoms are stronger, making the overall structure harder and more robust.
In simple words: Alkaline earth metals are harder than alkali metals because they have two outer electrons instead of just one. These extra electrons make the bonds between the metal atoms much stronger, so the metal feels harder.

🎯 Exam Tip: Remember that metallic bond strength generally increases with the number of valence electrons and decreases with atomic size, impacting properties like hardness and melting point.

 

Question 41. How is plaster of paris prepared?
Answer: Plaster of Paris is a hemihydrate of calcium sulphate, meaning it contains half a molecule of water for every calcium sulphate unit. It is made by heating gypsum, which is calcium sulphate dihydrate \( (\text{CaSO}_4\cdot 2\text{H}_2\text{O}) \), to a temperature of 393 Kelvin (K). This heating process removes most of the water molecules from the gypsum. Above 393 K, all the water of crystallization is lost, and anhydrous calcium sulphate \( (\text{CaSO}_4) \) is formed, which is sometimes called 'dead burnt plaster'. The controlled heating ensures that only a specific amount of water is removed, creating the hemihydrate form.
\( 2\text{CaSO}_4\cdot 2\text{H}_2\text{O(s)} \rightarrow 2\text{CaSO}_4\cdot \text{H}_2\text{O} + 3\text{H}_2\text{O} \)
In simple words: To make Plaster of Paris, you heat a mineral called gypsum. Heating it carefully takes away most of its water, leaving behind a special kind of calcium sulphate that has only a little water left.

🎯 Exam Tip: Pay attention to the temperature control when preparing Plaster of Paris; overheating can lead to "dead burnt plaster" which loses its setting properties.

 

Question 42. Give the uses of gypsum.
Answer: Gypsum has a wide range of uses across several industries and applications:
1. It is widely used in the building industry for making drywalls, plasterboards, and as a finish for walls and ceilings. It also forms partitions.
2. Gypsum is crucial for producing Plaster of Paris, which is then used as a sculpting material and for creating casts of statues and busts.
3. The alabaster variety of gypsum was historically used by sculptors in ancient Egypt and Mesopotamia.
4. In agriculture, it serves as a soil additive, conditioner, and fertilizer, helping to loosen compact soil and providing essential calcium and sulfur for plant growth.
5. Gypsum is an ingredient in toothpaste, shampoos, and hair products, where it acts as a binding and thickening agent.
6. It is a component of Portland cement, where it slows down the setting process, allowing concrete to be worked for longer.
7. Gyylon is also used in making surgical and orthopaedic casts, such as surgical splints and casting molds.
In simple words: Gypsum is used to build walls, make sculptures, help plants grow, thicken products like toothpaste, and slow down how fast cement sets.

🎯 Exam Tip: When listing uses, group similar applications together to ensure clarity and avoid repetition, like combining all construction-related uses.

 

Question 43. Describe briefly the biological importance of Calcium and magnesium.
Answer:
Magnesium:
1. An average adult human body contains about 25 grams of magnesium.
2. Magnesium is very important for many biochemical reactions that are helped by enzymes.
3. It acts as a necessary helper (co-factor) for all enzymes that use ATP (energy molecule) for transferring phosphates and releasing energy.
4. It is also vital for making DNA and helps keep DNA stable and working correctly.
5. Magnesium helps in keeping the body's electrolytes balanced, which is important for many bodily functions.
6. Not having enough magnesium can cause muscle spasms (convulsions) and nerve irritation.
7. Magnesium is a key part of chlorophyll, the green pigment responsible for photosynthesis in plants.
Calcium:
1. Calcium is a main building block of bones and teeth, making them strong. Bones act as a reserve for calcium in the body.
2. It is also found in the blood, and its level is controlled by hormones like calcitonin and parathyroid hormone.
3. A lack of calcium in the blood makes it take longer for blood to clot. It is also important for muscles to contract and relax properly.
In simple words: Magnesium helps enzymes work, DNA form, and keeps body fluids balanced. Calcium builds strong bones and teeth, helps blood clot, and makes muscles work.

🎯 Exam Tip: For biological importance questions, focus on key functions and their impact on health, and where the element is found in the body.

 

Question 44. Which would you expect to have a higher melting point, magnesium oxide or magnesium fluoride? Explain your reasoning.
Answer: Magnesium oxide \( (\text{MgO}) \) would have a higher melting point than magnesium fluoride \( (\text{MgF}_2) \). The melting point of magnesium oxide is \( 2852^\circ\text{C} \), while that of magnesium fluoride is \( 1263^\circ\text{C} \).
The strength of ionic bonds, which determines the melting point, depends on two main things: the ionic radius and the charge of the ions. Magnesium ions \( (\text{Mg}^{2+}) \) and oxide ions \( (\text{O}^{2-}) \) both have charges of \( +2 \) and \( -2 \) respectively. These charges are larger than the \( -1 \) charge of fluoride ions \( (\text{F}^{-}) \). Additionally, the oxygen ion \( (\text{O}^{2-}) \) is smaller than the fluoride ion \( (\text{F}^{-}) \). When ions have smaller radii and higher charges, the bond length between them becomes shorter, and the electrostatic attraction between them becomes much stronger. Therefore, the ionic bond between magnesium and oxygen in \( \text{MgO} \) is stronger than the bond between magnesium and fluoride in \( \text{MgF}_2 \), requiring more energy to break, resulting in a higher melting point.
In simple words: Magnesium oxide has a higher melting point because its ions have stronger charges and are smaller. This makes the bonds between them much stronger than in magnesium fluoride, so it needs a lot more heat to melt.

🎯 Exam Tip: Remember that melting points of ionic compounds are primarily determined by the strength of the ionic bonds, which increases with higher ionic charges and smaller ionic radii.

11th Chemistry Guide Alkali and Alkaline Earth Metals Additional Questions and Answers

I. Choose the best Answer:

 

Question 1. The reducing property of alkali metals follows the order
(a) Na < K < Rb < Cs < Li
(b) K < Na < Rb < Cs < Li
(c) Li < Cs < Rb < K < Na
(d) Rb < Cs < K < Na < Li
Answer: (a) Na < K < Rb < Cs < Li
In simple words: The ability of alkali metals to reduce other substances generally increases as you go down the group, with lithium being the strongest reducing agent in this list.

🎯 Exam Tip: For reducing properties of alkali metals, consider their tendency to lose electrons; a more positive standard electrode potential indicates a stronger reducing agent.

 

Question 2. Arrange the following in increasing order of hydration enthalpy.
(a) Rb\( ^+ \) > Li\( ^+ \) > Na\( ^+ \) > K\( ^+ \) > Cs\( ^+ \)
(b) Cs\( ^+ \) > Rb\( ^+ \) > K\( ^+ \) > Na\( ^+ \) > Li\( ^+ \)
(c) Li\( ^+ \) > Na\( ^+ \) > K\( ^+ \) > Rb\( ^+ \) > Cs\( ^+ \)
(d) K\( ^+ \) > Na\( ^+ \) > Li\( ^+ \) > Rb\( ^+ \) > Cs\( ^+ \)
Answer: (c) Li\( ^+ \) > Na\( ^+ \) > K\( ^+ \) > Rb\( ^+ \) > Cs\( ^+ \)
In simple words: Hydration enthalpy is highest for the smallest ion (lithium) and decreases as the ion size gets bigger (towards cesium).

🎯 Exam Tip: Remember that smaller ions have a higher charge density, which leads to stronger attraction to water molecules and thus higher hydration enthalpy.

 

Question 3. Li does not resemble other alkali metals in which of the following property?
(a) Li\( _2 \)\( \text{CO}_3 \) decomposes into oxides while other alkali carbonates re thermally stable
(b) LiCl is predominantly covalent
(c) Li\( _3 \)\( \text{N} \) stable
(d) All of the options
Answer: (d) All of the options
In simple words: Lithium is different from other alkali metals in many ways, including how its carbonate breaks down, its chloride's bond type, and the stability of its nitride.

🎯 Exam Tip: Lithium shows anomalous behavior compared to other alkali metals due to its very small size and high polarizing power, affecting properties like thermal stability and bond character.

 

Question 4. 1 mol of a substance (X) was treated with an excess of water, 2 mol of readily combustible gas were . produced along with solution which when reacted with \( \text{CO}_2 \) gas produced a white turbidity. The substance (X) could be
(a) Ca
(b) CaH\( _2 \)
(c) Ca(OH)\( _2 \)
(d) Ca(NO\( _3 \))\( _2 \)
Answer: (b) CaH\( _2 \)
In simple words: The unknown substance is calcium hydride, as it reacts with water to produce flammable hydrogen gas and a solution that forms a cloudy white substance when carbon dioxide is added.

🎯 Exam Tip: For reaction-based MCQs, systematically test each option against the given observations (gas evolved, turbidity formed) to find the substance that fits all criteria.

 

Question 5. The alkali metal used in photoelectric cells is
(a) Na
(b) Cs
(c) Rb
(d) Fr
Answer: (b) Cs
In simple words: Cesium is the alkali metal mainly used in photoelectric cells because it easily releases electrons when light shines on it.

🎯 Exam Tip: Remember that elements with lower ionization energy are suitable for photoelectric cells because they require less energy to eject electrons.

 

Question 6. Na\( _2 \)\( \text{O}_2 \) has light yellow colour. This is due to
(a) presence of unpaired electron in the molecule
(b) presence of trace of NaO\( _2 \)
(c) presence of KO\( _2 \) ass an impurity
(d) None of the options
Answer: (b) presence of trace of NaO\( _2 \)
In simple words: Sodium peroxide usually looks pale yellow because it contains very small amounts of sodium superoxide as an impurity.

🎯 Exam Tip: Be aware that even tiny amounts of impurities can significantly affect the observed physical properties, such as color, of a compound.

 

Question 7. Be\( _2 \)\( \text{C} \) + 4\( \text{H}_2\text{O} \) \( \rightarrow \) 2X + \( \text{CH}_4 \) X + 2\( \text{HCl} \) + 2\( \text{H}_2\text{O} \) \( \rightarrow \) Y X and Y formed in the above two reactions is
(a) BeCO\( _3 \) and Be(OH)\( _2 \) respectively
(b) Be(OH)\( _2 \) and BeCl\( _2 \) respectively
(c) Be(OH)\( _2 \) and [Be(OH)\( _4 \)]Cl\( _2 \) respectively
(d) [Be(OH)\( _4 \)]\( ^{2-} \) and BeCl\( _2 \) respectively
Answer: (c) Be(OH)\( _2 \) and [Be(OH)\( _4 \)]Cl\( _2 \) respectively
In simple words: In these reactions, the substance X is beryllium hydroxide, and Y is the complex compound [Be(OH)\( _4 \)]Cl\( _2 \), formed after further reaction.

🎯 Exam Tip: When solving multi-step reaction problems, first identify the product of the initial reaction (X) and then use it as a reactant to find the final product (Y).

 

Question 8. When sodium reacts with excess of oxygen, oxidation number of oxygen changes from
(a) 0 to -1
(b) 0 to 2
(c) -1 to -2
(d) +1 to -1
Answer: (a) 0 to -1
In simple words: When sodium reacts with a lot of oxygen, the oxygen changes from its pure form (oxidation number 0) to a peroxide state (oxidation number -1).

🎯 Exam Tip: Remember that pure elemental oxygen \( (\text{O}_2) \) has an oxidation state of 0, but in peroxides like sodium peroxide \( (\text{Na}_2\text{O}_2) \), oxygen's oxidation state is -1.

 

Question 9. Magnesium burns in air to give
(a) MgO
(b) MgCO\( _3 \)
(c) MgCO\( _3 \)
(d) MgO and Mg\( _3 \)\( \text{N}_2 \)
Answer: (d) MgO and Mg\( _3 \)\( \text{N}_2 \)
In simple words: When magnesium burns in air, it reacts with both oxygen and nitrogen to form two products: magnesium oxide and magnesium nitride.

🎯 Exam Tip: Recall that air is a mixture of gases, mainly nitrogen and oxygen, so burning in air often leads to reactions with both components, not just oxygen.

 

Question 10. The composition of common baking powder is
(a) starch, sodium bicarbonate, citric acid
(b) Sodium bicarbonate, tartaric acid
(c) starch, sodium bicarbonate, citric acid
(d) Starch, sodium bicarbonate, calcium hydrogen phosphate.
Answer: (d) Starch, sodium bicarbonate, calcium hydrogen phosphate.
In simple words: Baking powder is a mixture that usually contains starch, baking soda (sodium bicarbonate), and a type of acidic salt like calcium hydrogen phosphate.

🎯 Exam Tip: Baking powder requires both an alkali (bicarbonate) and an acid (often a phosphate or tartaric acid) along with a filler (starch) to ensure a controlled release of carbon dioxide for leavening.

 

Question 11. The word 'alkali' used for alkali metals indicates
(a) ashes of plants
(b) metallic luster
(c) soft metals
(d) reactive metals
Answer: (a) ashes of plants
In simple words: The term "alkali" for alkali metals comes from the fact that their carbonates were originally found in the ashes of plants.

🎯 Exam Tip: Historical origins of chemical terms can sometimes provide clues about the properties or sources of elements and compounds.

 

Question 12. Which salt can be used to identify coloured cation
(a) borax
(b) microcosmic salt
(c) both (a) and (b)
(d) None of the options
Answer: (c) both (a) and (b)
In simple words: Both borax and microcosmic salt can be used in tests to find out if a metal ion is present by observing the color it makes when heated.

🎯 Exam Tip: The borax bead test and microcosmic salt bead test are qualitative analysis techniques that use the characteristic colors formed by metal ions with these salts at high temperatures.

 

Question 13. Select the correct statement
LiOH > NaOH > KOH > RbOH
Li\( _2 \)\( \text{CO}_3 \) > Na\( _2 \)\( \text{CO}_3 \) > K\( _2 \)\( \text{CO}_3 \) > Rb\( _2 \)\( \text{CO}_3 \)
(a) Solubility of alkali hydroxides is in order
(b) Solubility of alkali carbonates is in order
(c) both are correct
(d) None is correct
Answer: (b) Solubility of alkali carbonates is in order
In simple words: The statement about the solubility order of alkali carbonates, where lithium carbonate is most soluble and rubidium carbonate is least soluble, is correct.

🎯 Exam Tip: Remember that for alkali metal hydroxides, solubility increases down the group, while for alkali metal carbonates, thermal stability and solubility often follow opposite trends due to polarizing power.

 

Question 14. Which fumes in air?
(a) BeCl\( _2 \)
(b) MgCl\( _2 \)
(c) CaCl\( _2 \)
(d) BaCl\( _2 \)
Answer: (a) BeCl\( _2 \)
In simple words: Beryllium chloride produces fumes in the air because it reacts with moisture in the air.

🎯 Exam Tip: Many covalent halides fume in moist air due to hydrolysis, forming hydrogen halides that appear as fumes.

 

Question 15. Which of the following ions form a hydroxide highly soluble in water?
(a) Ni\( ^{2+} \)
(b) K\( ^{2+} \)
(c) Zn\( ^{2+} \)
(d) Al\( ^{3+} \)
Answer: (b) K\( ^{2+} \)
In simple words: Potassium ions form hydroxides that dissolve very well in water.

🎯 Exam Tip: Hydroxides of Group 1 metals (like potassium) are generally highly soluble in water, as are hydroxides of the heavier Group 2 metals. However, K forms K\( ^+ \) not K\( ^{2+} \). Given the options and chosen answer, it implies K is the intended answer despite the typo in charge. Let's assume K\( ^+ \) was intended.

 

Question 16. Which causes nerve signals in animals?
(a) Electrical potential gradient due to transfer of K\( ^+ \) ions
(b) Electrical potential gradient due to transfer of Na\( ^+ \) ions in (Na\( ^+ \) - K\( ^+ \)) pumps
(c) Electrical potential gradient set up due to transfer of Ca\( ^{2+} \) ions
(d) No nerve signal exists in animals.
Answer: (b) Electrical potential gradient due to transfer of Na\( ^+ \) ions in (Na\( ^+ \) - K\( ^+ \)) pumps
In simple words: Nerve signals are made by changes in electrical charge that happen when sodium and potassium ions move in and out of nerve cells, controlled by special pumps.

🎯 Exam Tip: The sodium-potassium pump is crucial for maintaining the electrochemical gradient across neuron membranes, which is fundamental for nerve impulse transmission.

 

Question 17. The carbide of which of the following metals on hydrolysis gives allylene or propyne?
(a) Be
(b) Ca
(c) Al
(d) Mg
Answer: (d) Mg
In simple words: When magnesium carbide reacts with water, it produces a gas called propyne, also known as allylene.

🎯 Exam Tip: Different metal carbides yield different hydrocarbons upon hydrolysis, a property used to distinguish them.

 

Question 18. Which of the follow \( \text{H}_2\text{O} \) wing reaction produces hydrogen?
(a) Mg + \( \text{H}_2\text{O} \)
(b) H\( _2 \)\( \text{S}_4\text{O}_8 \) + \( \text{H}_2\text{O} \)
(c) BaO\( _2 \) + \( \text{HCl} \)
(d) Na\( _2 \)\( \text{O}_2 \) + 2\( \text{HCl} \)
Answer: (a) Mg + \( \text{H}_2\text{O} \)
In simple words: Magnesium reacting with water creates hydrogen gas. This is a common way to produce hydrogen.

🎯 Exam Tip: Metals above hydrogen in the reactivity series react with water or acids to produce hydrogen gas. Magnesium reacts with cold water, albeit slowly, to produce hydrogen and magnesium hydroxide.

 

Question 19. A major constituent of Portland cement (except lime) is
(a) Silica
(b) Alumina
(c) Iron oxide
(d) Magnesia
Answer: (a) Silica
In simple words: Besides lime, silica is one of the main ingredients that make up Portland cement.

🎯 Exam Tip: Common constituents of cement include lime \( (\text{CaO}) \), silica \( (\text{SiO}_2) \), alumina \( (\text{Al}_2\text{O}_3) \), and iron oxide \( (\text{Fe}_2\text{O}_3) \), with lime and silica being the most abundant.

 

Question 20. Which of the following is known as a variety of gypsum ?
(a) CaCO\( _3 \)
(b) CaSO\( _4 \)
(c) plaster of paris
(d) gypsum
Answer: (d) gypsum
In simple words: Plaster of Paris is a modified form that comes from gypsum; thus, gypsum itself is not a "variety" of gypsum. The question here is asking which is a variety of gypsum, but "gypsum" is given as an option, which is incorrect. Given the options, perhaps it means which option IS gypsum, or which is not a variety. Let's re-evaluate. The question is "Which of the following is known as a variety of gypsum ?". If (d) is "gypsum", it cannot be a variety of itself. Plaster of Paris is formed FROM gypsum. However, the OCR gives (d) gypsum, and the answer is (d) gypsum. This indicates the question might be malformed or implying "which of these options *is* gypsum". Based on the OCR output, it appears the intention was for the answer to be something other than itself. If the options are all possible forms or related compounds, and gypsum is one of them, the question is nonsensical. Let's assume the question meant to ask "Which of the following is *gypsum*?" and (d) is the answer. For the "In simple words" and "Exam Tip", I will work with the assumption of the question being directly about identifying gypsum or a common variant if one were intended from options. Given the specific options, if it asks for a 'variety', plaster of paris (c) is derived from gypsum but not a variety. Calcite is CaCO3. Anhydrite is CaSO4. Since (d) is simply 'gypsum', and that is the selected answer, it's a direct identification.

🎯 Exam Tip: Understand the difference between a compound (like gypsum), its derivatives (like Plaster of Paris), and its various forms or minerals, which might also be called 'varieties' (e.g., alabaster is a variety of gypsum, but not listed here).

 

Question 21. The elements belongs to group-1 are called as
(a) Alkali metals
(b) Alkaline earth metals
(c) halogens
(d) chalcogens
Answer: (a) Alkali metals
In simple words: Elements in the first group of the periodic table are known as alkali metals.

🎯 Exam Tip: Familiarize yourself with the common names of important groups in the periodic table, as these are fundamental classifications.

 

Question 22. Which one of the following is a radioactive element of alkali metal?
(a) Cesium
(b) Francium
(c) Potassium
(d) Sodium
Answer: (b) Francium
In simple words: Francium is the alkali metal that is radioactive, meaning its atoms are unstable and break down over time.

🎯 Exam Tip: Remember that radioactivity generally increases for heavier elements in a group; Francium is the heaviest naturally occurring alkali metal.

 

Question 23. Match the correct pair Element:

(a) A – ii, B – iii, C – i
(b) A – i, B – ii, C – iii
(c) A – ii, B – i, C – iii
(d) A – i, B – iii, C – ii
Answer: (a) A – ii, B – iii, C – i
In simple words: This match correctly pairs lithium with spodumene, sodium with rock salt, and potassium with sylvite, showing their natural mineral sources.

🎯 Exam Tip: Memorize the common ore names and their corresponding metals, as this knowledge is frequently tested in chemistry.

 

Question 24. The colour of potassium salt in flame is
(a) Crimson red
(b) Lilac
(c) Blue
(d) Yellow
Answer: (b) Lilac
In simple words: When potassium salts are heated in a flame, they produce a distinctive lilac (pale purple) color.

🎯 Exam Tip: Flame tests are important for identifying alkali metals; specific colors correspond to specific elements due to electron transitions.

 

Question 25. Lithium reacts directly with carbon to form
(a) Li\( _2 \)\( \text{C}_2 \)
(b) Li\( _2 \)\( \text{C} \)
(c) LiC\( _2 \)
(d) LiC
Answer: (a) Li\( _2 \)\( \text{C}_2 \)
In simple words: Lithium reacts directly with carbon to create lithium carbide, which has the chemical formula \( \text{Li}_2\text{C}_2 \).

🎯 Exam Tip: Unlike other alkali metals, lithium directly reacts with carbon to form lithium carbide, which is a key distinguishing property.

 

Question 26. Lithium shows diagonal relationship with
(a) Beryllium
(b) Carbon
(c) Magnesium
(d) Calcium
Answer: (c) Magnesium
In simple words: Lithium has similar chemical properties to magnesium, which is diagonally positioned to it in the periodic table.

🎯 Exam Tip: The diagonal relationship occurs between elements of period 2 and period 3 in successive groups, showing similar properties due to comparable charge density.

 

Question 27. Which of the following element forms monoxide and peroxide?
(a) Lithium
(b) Potassium
(c) Rubedium
(d) Sodium
Answer: (d) Sodium
In simple words: Sodium can form both a monoxide and a peroxide when it reacts with oxygen.

🎯 Exam Tip: Alkali metals react with oxygen to form different oxides: lithium primarily forms monoxide, sodium forms peroxide, and heavier alkali metals (K, Rb, Cs) form superoxides.

 

Question 28. Choose the correct pair:

(a) A – iii, B – i, C – iv, D – ii
(b) A – ii, B – iii, C – iv, D – i
(c) A – iv, B – ii, C – iii, D – i
(d) A – ii, B – iv, C – i, D – iii
Answer: (a) A – iii, B – i, C – iv, D – ii
In simple words: This match correctly links \( \text{Pb}(\text{Me})_4 \) to anti-knock additives, \( \text{KCl} \) to fertilizer, \( \text{Pb-Al} \) alloy to aircraft parts, and Cesium \( (\text{Cs}) \) to photoelectric cells, highlighting their practical uses.

🎯 Exam Tip: Understand the applications of common chemical compounds and elements; matching questions often test this practical knowledge.

 

Question 29. Sodium reacts with acetylene to give
(a) Sodium ethoxide
(b) Sodium acetylide
(c) Sodium hydroxide
(d) Sodamide
Answer: (b) Sodium acetylide
In simple words: When sodium reacts with acetylene, it forms a compound called sodium acetylide. This is a common reaction where a metal replaces hydrogen from a special type of carbon compound.

🎯 Exam Tip: Remember that sodium is highly reactive and readily reacts with acidic hydrogens, such as those found in terminal alkynes like acetylene.

 

Question 30. The products obtained on reaction of Na2O2 with water are
(a) NaOH and H2O
(b) NaOH and H2O2
(c) Na2O and H2O2
(d) NaOH, Na2O
Answer: (b) NaOH and H2O2
In simple words: When sodium peroxide mixes with water, it creates sodium hydroxide and hydrogen peroxide. This reaction shows how strong an oxidizing agent sodium peroxide is.

🎯 Exam Tip: Be aware that metal peroxides like \( \text{Na}_2\text{O}_2 \) react with water to form hydroxides and hydrogen peroxide, not simply metal oxides.

 

Question 31. Choose the correct statement/s is are correct about alkali metals.
1. The oxides and peroxides are colourless when pure but the superoxides are yellow or orange in colour.
2. The peroxides are diamagnetic while the superoxides are paramagnetic.
3. Sodium peroxide is widely used as an oxidizing agent.
4. The alkali metal hydroxides are weak bases.
Answer: (c) 1, 2 and 3
In simple words: Statements 1, 2, and 3 are correct. Pure alkali metal oxides and peroxides are colorless, but superoxides are yellow or orange. Peroxides are not magnetic, while superoxides are. Sodium peroxide is also often used to make other things oxidize.

🎯 Exam Tip: It's important to differentiate between the colors, magnetic properties, and basicity of alkali metal oxides, peroxides, and superoxides.

 

Question 32. In the above statements
Statement – 1: LiF has low solubility in water.
Statement – 2: LiF has low lattice enthalpy.
(a) 1 alone is correct.
(b) Both 1 and 2 are correct
(c) 2 alone is correct
(d) Both 1 and 2 are incorrect
Answer: (a) 1 alone is correct.
In simple words: Only statement 1 is true: Lithium fluoride (LiF) does not dissolve easily in water. Statement 2 is incorrect because LiF actually has a very strong bond (high lattice energy) due to the small sizes of the lithium and fluoride ions, which makes it less soluble.

🎯 Exam Tip: Remember that very small ions like \( \text{Li}^+ \) and \( \text{F}^- \) form extremely strong lattice bonds, leading to high lattice enthalpy and, consequently, low solubility in water.

 

Question 33. Alkali metals except ______ form solid bicarbom
(a) Sodium
(b) Potassium
(c) Cesium
(d) Lithium
Answer: (d) Lithium
In simple words: Lithium is the only alkali metal that does not form a solid bicarbonate. All the other alkali metals can form bicarbonates that are solid.

🎯 Exam Tip: The small size of the lithium ion makes it behave differently from other alkali metals, including its inability to form stable solid bicarbonates.

 

Question 34. The ammonia used in the Solvay proves- recovered by using
(a) calcium chloride
(b) Calcium hydroxide
(c) calcium carbonate
(d) calcium oxide
Answer: (b) Calcium hydroxide
In simple words: In the Solvay process, ammonia is recycled and reused with the help of calcium hydroxide. This helps make the process more cost-effective.

🎯 Exam Tip: Understanding the recovery steps in industrial chemical processes, such as the Solvay process, is crucial for grasping efficiency and sustainability.

 

Question 35. The by-product formed in the Solvay process
(a) calcium chloride
(b) calcium hydroxide
(c) calcium carbonate
(d) ammonium chloride
Answer: (a) calcium chloride
In simple words: Calcium chloride is the main extra product created during the Solvay process, which is used to make sodium carbonate.

🎯 Exam Tip: For industrial processes, it's important to know not only the main products but also the significant by-products and their uses or disposal considerations.

 

Question 36. Sodium carbonate decahydrate on heating ab 373K gives
(a) Na2CO3.3H2O
(b) N2CO3.5H2O
(c) Na2CO3
(d) Na2CO3.H2O
Answer: (d) Na2CO3.H2O
In simple words: When sodium carbonate decahydrate is heated to about 373 Kelvin, it loses many of its water molecules and turns into sodium carbonate monohydrate, which means it has only one water molecule left.

🎯 Exam Tip: Remember the different hydrated forms of sodium carbonate and the specific temperatures at which they lose water molecules to transform into other hydrates or anhydrous forms.

 

Question 37. _______ is used water treatment to convert the hard water to soft water.
(a) Sodium chloride
(b) Sodium bicarbonate
(c) Sodium hydroxide
(d) Sodium carbonate
Answer: (d) Sodium carbonate
In simple words: Sodium carbonate, also known as washing soda, is used to treat hard water by removing minerals like calcium and magnesium, making it soft.

🎯 Exam Tip: Understand the chemistry behind water softening processes, particularly how sodium carbonate precipitates out the hardness-causing ions.

 

Question 38. The product obtained on saturating a solution o sodium carbonate with carbon dioxide is,-
(a) sodium bicarbonate
(b) sodium hydroxide
(c) sodium chloride
(d) sodium peroxide.
Answer: (a) sodium bicarbonate
In simple words: If you add a lot of carbon dioxide gas to a solution of sodium carbonate, it will produce sodium bicarbonate. This is an important reaction in many industrial processes.

🎯 Exam Tip: Recall that bubbling carbon dioxide through a carbonate solution typically leads to the formation of bicarbonates.

 

Question 39. Choose the correct pair:
(A) Sodium chloride (i) Petroleum refining
(B) Sodium Carbonate (ii) domestic use
(C) Sodium bicarbonate (iii) laundering
(D) Sodium Hydroxide (iv) fire extinguisher
Answer: (b) A – ii, B – iii, C – iv, D – i
In simple words: Sodium chloride is used at home. Sodium carbonate helps with washing clothes. Sodium bicarbonate can be found in fire extinguishers. Sodium hydroxide is used in processing petroleum.

🎯 Exam Tip: Familiarize yourself with the common names and primary applications of various sodium compounds to quickly match them with their uses.

 

Question 40. The ______ used in baking cakes, pastries etc., is
(a) sodium chloride
(b) sodium carbonate
(c) sodium bicarbonate
(d) sodium hydroxide
Answer: (c) sodium bicarbonate
In simple words: Sodium bicarbonate, commonly known as baking soda, is added to cakes and pastries to make them soft and rise.

🎯 Exam Tip: Understand how leavening agents like sodium bicarbonate work by releasing carbon dioxide gas during baking to create a light and airy texture.

 

Question 41. ______ pump play an important role in transmitting nerve signals.
(a) sodium-Magnesium
(b) sodium-potassium
(c) sodium-calcium
(d) sodium-lithium
Answer: (b) sodium-potassium
In simple words: The sodium-potassium pump is essential for sending messages along our nerves and keeping our cells working correctly by moving sodium and potassium ions.

🎯 Exam Tip: The sodium-potassium pump is a vital active transport mechanism in biological systems, crucial for maintaining electrochemical gradients across cell membranes.

 

Question 42. Fluoraptite is the ore of
(a) magnesium
(b) beryllium
(c) potassium
(d) calcium
Answer: (d) calcium
In simple words: Fluorapatite is a natural rock formation from which we can extract calcium. It's a key source for this important mineral.

🎯 Exam Tip: Knowing the common ores for different metals helps understand where these elements come from in nature and how they are sourced.

 

Question 43. The fifth most abundant element in the earth's crust is
(a) magnesium
(b) beryllium
(c) calcium
(d) strontium
Answer: (c) calcium
In simple words: Calcium is the fifth most common element found in the solid outer layer of the Earth. It exists in many mineral forms like limestone.

🎯 Exam Tip: Familiarity with the relative abundance of elements in the Earth's crust provides context for their natural distribution and economic importance.

 

Question 44. Strontium nitrate give ______ colour in fire works.
(a) violet
(b) bright red
(c) green
(d) orange
Answer: (b) bright red
In simple words: Strontium nitrate makes fireworks glow with a vivid bright red color. This happens because the strontium atoms get energized and release light.

🎯 Exam Tip: Linking specific metal salts to the colors they produce in flames (flame tests) is a common way to identify them and is directly applicable to fireworks chemistry.

 

Question 45. Which of the alkaline earth metal has highest hydration enthalpy?
(a) Be
(b) Mg
(c) Ca
(d) Sr
Answer: (a) Be
In simple words: Beryllium has the highest hydration energy among alkaline earth metals. This is because its ions are the smallest and can attract water molecules most strongly.

🎯 Exam Tip: Hydration enthalpy is generally highest for ions with small size and high charge, as they can interact more intensely with polar water molecules.

 

Question 46. The anomalous properties of beryllium is mainly due to its
1. small size
2. low electronegativity
3. high ionization energy
4. low polarizing power.
Answer: (d) 1 and 3
In simple words: Beryllium acts differently from other metals in its group mainly because its atoms are very small and it takes a lot of energy to remove its electrons (high ionization energy).

🎯 Exam Tip: The anomalous behavior of the first element in each group (like beryllium) is often attributed to its exceptionally small size, high charge density, and strong tendency to form covalent bonds.

 

Question 47. ______ and ______ ions have strong tendency to form complexes.
(a) Be and Al
(b) Be and Mg
(c) Ca and Sr
(d) Be and B
Answer: (a) Be and Al
In simple words: Beryllium and aluminum ions like to form complex compounds easily. This is because they are small and have a strong positive charge, which helps them attract other molecules.

🎯 Exam Tip: Small, highly charged ions (like \( \text{Be}^{2+} \) and \( \text{Al}^{3+} \)) are effective Lewis acids and tend to form stable complexes with electron-donating ligands.

 

Question 48. ______ is used as radiation windows for X-ray tubes.
(a) Mg
(b) Be
(c) Na
(d) Ca
Answer: (b) Be
In simple words: Beryllium is used for the windows in X-ray machines. It works well because X-rays can pass through it easily without much absorption.

🎯 Exam Tip: Beryllium's low atomic number and high transparency to X-rays make it a unique and crucial material in specialized equipment like X-ray tubes.

 

Question 49. A compound of calcium used in makig surgical and orthopedic casts is
(a) Dolomite
(b) Gypsum
(c) Feldspar
(d) plaster of paris
Answer: (d) plaster of paris
In simple words: Plaster of Paris, a compound of calcium, is used to create medical casts for supporting and healing broken bones. It hardens quickly when mixed with water.

🎯 Exam Tip: Plaster of Paris is chemically calcium sulfate hemihydrate, known for its rapid setting property when hydrated, which is ideal for medical casts and molding.

 

Question 50. ______ is a major component of bones and teeth.
(a) Na
(b) Be
(c) Ca
(d) Mg
Answer: (c) Ca
In simple words: Calcium is a very important part of our bones and teeth, helping to make them strong and healthy. It's mostly found as calcium phosphate.

🎯 Exam Tip: Recall the biological significance of calcium as the primary mineral component of the skeletal system in humans and animals.

II. Very Short Question And Answers (2 Marks)

 

Question 1. What are s-block elements?
Answer: S-block elements are those found in Group 1 and Group 2 of the modern periodic table. These elements have their outermost electron (or electrons) in an s-orbital. Group 1 elements are called alkali metals, and Group 2 elements are called alkaline earth metals. They are known for their reactivity and metallic properties.
In simple words: S-block elements are metals in the first two columns of the periodic table. The first column metals are alkali metals, and the second column metals are alkaline earth metals.

🎯 Exam Tip: Remember that the 's' in s-block refers to the s-orbital where the valence electrons are located, determining many of their chemical properties.

 

Question 2. What are alkali metals?
Answer: Alkali metals are a group of elements found in Group 1 of the periodic table. This group includes lithium, sodium, potassium, rubidium, cesium, and francium. They are known for being very soft, shiny, and highly reactive metals. They easily lose one electron to form positive ions and typically form strong basic oxides and hydroxides.
In simple words: Alkali metals are a group of very reactive, soft metals like lithium and sodium. They are in the first column of the periodic table and make strong basic compounds.

🎯 Exam Tip: Key characteristics of alkali metals include high reactivity, soft texture, and forming strong bases, which are important distinguishing features.

 

Question 3. Write the mineral source of lithium, sodium and potassium.
Answer:

Lithium is commonly extracted from spodumene. Sodium's primary mineral source is rock salt, which is mainly sodium chloride. Potassium is largely obtained from sylvite, a mineral composed primarily of potassium chloride.
In simple words: Lithium comes from spodumene. Sodium comes from rock salt. Potassium comes from sylvite.

🎯 Exam Tip: Remember the common mineral names for each alkali metal, as these are important for understanding their natural occurrence and extraction.

 

Question 4. Why does the ionization enthalpy of alkali metals decreases in a group?
Answer: The ionization enthalpy of alkali metals decreases as you move down the group in the periodic table. This happens because the atomic size increases, meaning the outermost electron is further from the nucleus. Additionally, the number of inner electron shells increases, which creates a stronger shielding effect. This shielding reduces the pull of the nucleus on the valence electron, making it easier to remove, thus lowering the ionization enthalpy.
In simple words: Ionization energy goes down for alkali metals as you go lower in the group. This is because atoms get bigger, and inner electrons block the pull of the nucleus, making it easier to take away the outer electron.

🎯 Exam Tip: Understand the trends in ionization enthalpy across the periodic table, especially the effect of atomic size and shielding on the energy required to remove an electron.

 

Question 5. The second ionization enthalpies of alkali metals are very high. Give reason.
Answer: The second ionization enthalpy of alkali metals is very high because, after losing one electron, they achieve a stable electron configuration similar to that of a noble gas. Removing a second electron would mean breaking this very stable noble gas configuration, which requires a large amount of energy.
In simple words: Alkali metals need a lot of energy to lose a second electron. After losing one electron, they become very stable, like noble gases, so it's hard to take another electron away.

🎯 Exam Tip: Always connect the stability of an atom or ion to its electron configuration, especially noble gas configurations, to explain ionization energy trends.

 

Question 6. Why is the lithium salts are more soluble than the salts of other metals of group-1.
Answer: Lithium salts are often more soluble than the salts of other Group 1 metals. This higher solubility is mainly due to the strong hydration (solvation) of the small lithium ion (\( \text{Li}^+ \)). The small size of \( \text{Li}^+ \) allows it to attract and surround itself with many water molecules very effectively, releasing a lot of hydration energy which helps overcome the lattice energy of the salt. For example, lithium perchlorate (\( \text{LiClO}_4 \)) is much more soluble than other alkali metal perchlorates.
In simple words: Lithium salts dissolve better than other alkali metal salts. This is because the small lithium ion pulls water molecules very strongly, which helps the salt break apart and dissolve.

🎯 Exam Tip: Remember that the small size and high charge density of the lithium ion significantly influence its chemical properties, including solvation and solubility.

 

Question 7. What is diagonaol relatiobship?
Answer: Diagonal relationship is a similarity in properties observed between the first element of one group and the second element of the next group in the periodic table. For example, lithium (Group 1) shows similarities with magnesium (Group 2). This occurs because these elements have similar ionic sizes and comparable electronegativity values, which leads to similar chemical behaviors.
In simple words: Diagonal relationship means the first element of one group acts like the second element of the next group, for example, lithium acts like magnesium. They behave similarly because they have similar sizes and electronegativity.

🎯 Exam Tip: The diagonal relationship is a crucial concept for understanding how properties across the periodic table are influenced by size and electronegativity.

 

Question 8. Why does the solubility of carbonates and bicarbonates decreases in a group?
Answer: The solubility of carbonates and bicarbonates of alkali metals generally increases as you move down the group. This is because, as you move down, the size of the metal ion increases. The decrease in lattice energy (energy holding the ions in the solid crystal) is faster than the decrease in hydration energy (energy released when ions dissolve in water). When the lattice energy drops more quickly than the hydration energy, the overall energy balance favors dissolution, leading to increased solubility.
In simple words: Carbonates and bicarbonates dissolve more as you go down the group. This is because the crystal holding them together gets weaker faster than their ability to mix with water.

🎯 Exam Tip: For solubility trends, always consider the balance between lattice enthalpy and hydration enthalpy. A greater decrease in lattice enthalpy down a group often leads to increased solubility.

 

Question 9. Lithium carbonate is considerably less stable and decompose readily. Give reason.
Answer: Lithium carbonate (\( \text{Li}_2\text{CO}_3 \)) is much less stable and decomposes easily when heated compared to other alkali metal carbonates. This is because the small \( \text{Li}^+ \) ion has a strong polarizing effect on the large \( \text{CO}_3^{2-} \) ion, distorting it and making it less stable. This distortion makes it easier for the carbonate to break down into lithium oxide and carbon dioxide:
\( \text{Li}_2\text{CO}_3 \rightarrow \text{Li}_2\text{O} + \text{CO}_2 \)
In simple words: Lithium carbonate breaks down easily when heated. This happens because the tiny lithium ion pushes on the big carbonate ion, making it unstable.

🎯 Exam Tip: Remember that the small size of the lithium ion causes it to have a strong polarizing effect, which destabilizes large anions like carbonate.

 

Question 10. What is washing soda?
Answer: Washing soda is the common name for hydrated sodium carbonate, specifically sodium carbonate decahydrate (\( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \)). It appears as a white, crystalline solid and is widely used as a cleaning agent, laundry additive, and in water softening. It has a slightly alkaline nature which aids in cleaning.
In simple words: Washing soda is just sodium carbonate that has ten water molecules attached to it. It is a white crystal used for cleaning.

🎯 Exam Tip: Know the chemical name and formula for common household chemicals like washing soda (\( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \)).

 

Question 11. What is action of heating on sodium carbonate?
Answer: When sodium carbonate decahydrate is heated, it first loses most of its water of crystallization to form sodium carbonate monohydrate. If heating continues above 313 K, the monohydrate loses its remaining water, becoming completely anhydrous sodium carbonate (\( \text{Na}_2\text{CO}_3 \)), which is a white powder known as soda ash. This process involves two main steps:
\( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \xrightarrow{\text{heating}} \text{Na}_2\text{CO}_3 \cdot \text{H}_2\text{O} + 9\text{H}_2\text{O} \)
\( \implies \text{Na}_2\text{CO}_3 \cdot \text{H}_2\text{O} \xrightarrow{\text{heating above 313 K}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} \)
In simple words: Heating sodium carbonate with ten water molecules makes it first lose most water, leaving one water molecule. If you keep heating it above 313 Kelvin, it loses all its water and becomes a dry white powder called soda ash.

🎯 Exam Tip: Be familiar with the thermal decomposition of hydrated salts and the different stages of water loss, identifying the products at each specific temperature range.

 

Question 12. How does Lithium shows similar properties with magnesium in its chemical behavior?
Answer: Lithium shows a diagonal relationship with magnesium, meaning they have similar chemical behaviors in several ways. Both lithium and magnesium can react directly with nitrogen to form nitrides. They also both react with oxygen to form monoxides. Furthermore, both elements tend to form covalent compounds rather than purely ionic ones, and they are capable of forming complex compounds due to their small size and high charge density.
In simple words: Lithium acts like magnesium in some ways. Both react with nitrogen to make nitrides and with oxygen to make monoxides. They also like to form covalent bonds and complex compounds.

🎯 Exam Tip: The diagonal relationship is a key concept to explain similarities between elements like lithium and magnesium due to similar ionic sizes and electronegativities.

 

Question 13. Why are potassium and caesium, rather than lithium used in photoelectric cells?
Answer: Potassium and cesium are preferred over lithium for use in photoelectric cells because they have much lower ionization enthalpies. This means it requires less energy to remove an electron from their atoms. Consequently, when light falls on potassium or cesium, they easily release electrons, a property crucial for the functioning of photoelectric cells. Lithium, having a higher ionization enthalpy, does not release electrons as readily with visible light.
In simple words: Potassium and cesium are used in photoelectric cells instead of lithium because their electrons are easier to knock off with light. They need less energy to release electrons.

🎯 Exam Tip: Relate ionization enthalpy to the work function in photoelectric effect: elements with lower ionization enthalpy have a lower work function and are more efficient in photoelectric devices.

 

Question 14. Write the chemical formula of the following compounds.
(a) Chile salt petre; (b) marble; (c) Brine
Answer:
(a) Chile salt petre: \( \text{NaNO}_3 \) (Sodium nitrate). This is a naturally occurring mineral rich in nitrogen.
(b) Marble: \( \text{CaCO}_3 \) (Calcium carbonate). Marble is a metamorphic rock composed of recrystallized carbonate minerals.
(c) Brine: \( \text{NaCl} \) (Sodium chloride solution). Brine refers to a concentrated solution of salt, usually sodium chloride, in water.
In simple words: (a) Chile saltpetre is \( \text{NaNO}_3 \). (b) Marble is \( \text{CaCO}_3 \). (c) Brine is salty water, mainly \( \text{NaCl} \).

🎯 Exam Tip: Learn the common names and chemical formulas for important inorganic compounds, as this knowledge is fundamental in chemistry.

 

Question 15. The order ofionic mobility of the ions in aqueous solution is Cs+ > Rb+ > K+ > Na+. Account it.
Answer: The order of ionic mobility in an aqueous solution for alkali metal ions is \( \text{Cs}^+ > \text{Rb}^+ > \text{K}^+ > \text{Na}^+ > \text{Li}^+ \). This trend can be explained by the degree of hydration. Smaller ions, like \( \text{Li}^+ \), have a higher charge density and attract more water molecules, forming a larger hydrated ion. This larger "effective" size means they move slower through the solution. As you go down the group, the ionic size increases, but the charge density decreases, leading to less hydration. So, \( \text{Cs}^+ \) (which is the largest naked ion) attracts fewer water molecules and has the smallest effective hydrated size, allowing it to move fastest and have the highest ionic mobility.
In simple words: Smaller alkali metal ions in water, like lithium, get surrounded by many water molecules, making them big and slow. Larger ions, like cesium, attract fewer water molecules, so they stay smaller and move faster in water. This is why cesium moves fastest, and lithium moves slowest.

🎯 Exam Tip: Remember that in aqueous solutions, the *hydrated* size of an ion, not just its naked ionic radius, is the primary factor determining its mobility.

 

Question 16. (a) Lithium Iodide is more covalent than Lithium fluoride, fluoride, (b) Lattice enthalpy of LiF is maximum among all the alkali metals halides. Explain.
Answer:
(a) Lithium iodide (\( \text{LiI} \)) is more covalent than lithium fluoride (\( \text{LiF} \)). This is explained by Fajan's rule. The \( \text{Li}^+ \) ion is very small and has a high polarizing power. The iodide ion (\( \text{I}^- \)) is much larger and more easily polarized than the fluoride ion (\( \text{F}^- \)). The greater distortion of the electron cloud of \( \text{I}^- \) by \( \text{Li}^+ \) leads to a higher covalent character in \( \text{LiI} \).
(b) The lattice enthalpy of lithium fluoride (\( \text{LiF} \)) is the highest among all alkali metal halides. This is because both \( \text{Li}^+ \) and \( \text{F}^- \) ions are exceptionally small. Their small size leads to a very short inter-ionic distance and strong electrostatic forces of attraction, resulting in a very high lattice energy.
In simple words: (a) Lithium iodide is more covalent because the lithium ion can pull on the bigger iodide ion's electrons more strongly than it can on the smaller fluoride ion's electrons. (b) Lithium fluoride has the strongest bond (highest lattice energy) among all alkali metal halides. This is because both lithium and fluoride ions are very tiny, allowing them to pack very closely and stick together strongly.

🎯 Exam Tip: Apply Fajan's rules to predict covalent character based on cation size, anion size, and charge. Also, recall that lattice energy is inversely proportional to inter-ionic distance, meaning smaller ions result in higher lattice energy.

 

Question 17. Write notes on flame test for alkali metals.
Answer: A flame test is used to identify alkali metals by observing the unique color they impart to a non-luminous flame. When a small amount of an alkali metal salt, moistened with concentrated hydrochloric acid, is heated on a platinum wire in a Bunsen burner flame, the metal atoms absorb energy and get excited. As these excited electrons return to their ground state, they emit light of specific wavelengths, producing a characteristic color. For example, lithium gives a crimson red flame, sodium gives a golden yellow flame, and potassium gives a lilac (pale violet) flame. The hydrochloric acid helps convert the salt into a more volatile chloride, aiding vaporization.
In simple words: To do a flame test, you heat a bit of alkali metal salt in a flame. The heat makes the electrons jump, and when they fall back, they give off light in special colors. For example, lithium glows red, and potassium glows purple.

🎯 Exam Tip: Memorize the characteristic flame colors for common alkali metals (Li - crimson red, Na - golden yellow, K - lilac) as it's a standard qualitative analysis technique.

 

Question 18. Give two uses of alkali metals.
Answer: Alkali metals have various important uses:
1. Lithium is extensively used in making alloys. For instance, its alloy with lead forms 'white metal' for motor engine bearings, and its alloy with aluminum is vital for aircraft parts. Lithium is also a key component in thermonuclear reactions and batteries for electrochemical cells.
2. Sodium is crucial in industrial processes. It is used in the manufacturing of sodium peroxide, sodium cyanide, and is essential in organic reactions as a reducing agent. Sodium vapor lamps provide distinct yellow light for street lighting.
In simple words: 1. Lithium is used to make strong metal mixtures (alloys) for things like airplane parts and car engines. It's also in batteries. 2. Sodium is used in many industries, like making other chemicals, and in special street lamps that glow yellow.

🎯 Exam Tip: Focus on two distinct and significant uses for each alkali metal rather than just listing many, ensuring you can explain their importance.

 

Question 19. Write the uses of sodium bicarbonate.
Answer: Sodium bicarbonate, commonly known as baking soda, has several uses:
1. It is widely used as a leavening agent in baking to make cakes and bread rise by releasing carbon dioxide gas.
2. It acts as a mild antiseptic, helping to prevent infections on the skin.
3. It is an important component in certain types of fire extinguishers, where it releases carbon dioxide to smother flames.
4. It is also used as an antacid to relieve heartburn and indigestion.
In simple words: Sodium bicarbonate is used in baking, as a gentle germ-killer for skin, and in fire extinguishers to put out fires. It also helps with upset stomachs.

🎯 Exam Tip: Understand the versatility of sodium bicarbonate, from its role in cooking to its medical and safety applications, due to its mild alkaline and gas-producing properties.

 

Question 20. What are alkaline earth metals?
Answer: Alkaline earth metals are the elements found in Group 2 of the modern periodic table. This group includes beryllium, magnesium, calcium, strontium, barium, and radium. They are typically soft, silvery-white metals that are highly reactive and readily lose their two outermost electrons to form \( \text{+2} \) ions. Their compounds are commonly found in the Earth's crust.
In simple words: Alkaline earth metals are elements like beryllium, magnesium, and calcium, found in the second column of the periodic table. They are shiny metals that are very reactive.

🎯 Exam Tip: Remember that alkaline earth metals are in Group 2 and easily form \( \text{+2} \) ions, contrasting with alkali metals (Group 1, \( \text{+1} \) ions).

 

Question 21. Write notes on the physical state of alkaline earth metals.
Answer: Alkaline earth metals are generally silvery-white, shiny, and relatively soft metals, though harder than alkali metals. They have higher melting and boiling points compared to alkali metals in the same period. They are all solids at room temperature. Beryllium is quite hard, while magnesium and calcium are softer but still harder than alkali metals. These metals are typically found in various minerals and ores across the Earth's crust, like limestone for calcium and magnesite for magnesium.
In simple words: Alkaline earth metals are shiny, silvery-white, and solid at room temperature. They are harder than alkali metals and are found in many rocks on Earth.

🎯 Exam Tip: Compare the physical properties of alkaline earth metals with alkali metals to highlight trends and differences across the periodic table, such as their relative hardness and melting points.

 

Question 22. Write the uses of Beryllium.
Answer: Beryllium is used in several important ways: 1. It is used to make radiation windows for X-ray tubes and X-ray detectors because it has a low atomic number and absorbs very little X-ray radiation. 2. Sample holders in X-ray emission studies are often made of beryllium. 3. Because beryllium lets energetic particles pass through easily, it is used to build 'beam pipes' in particle accelerators. This helps scientists study tiny particles. 4. Due to its low density and its diamagnetic nature (it is not affected by magnetic fields), beryllium is used in various detectors.In simple words: Beryllium is used in X-ray equipment, particle accelerators, and detectors because it is light, absorbs little radiation, and lets particles pass through.

🎯 Exam Tip: When listing uses, always aim for at least two distinct applications to show comprehensive knowledge. Focus on unique properties like low atomic number or transparency to particles for beryllium.

 

Question 23. What are the uses of Strontium.
Answer: Strontium has a few key uses: 1. The isotope \( ^{90}Sr \) is used in cancer therapy. It is a radioactive isotope. 2. The ratio of \( ^{86}Sr \) to \( ^{86}Sr \) is commonly used in studies of oceans, teeth, animal migrations, and forensic science to trace origins. 3. Strontium is also used for dating rocks, which helps scientists understand the age of geological formations.In simple words: Strontium is used in medicine to treat cancer, to track origins in nature and forensics, and to help find the age of rocks.

🎯 Exam Tip: Remember to specify the isotope for cancer therapy. For other uses, linking strontium ratios to tracking and dating is a key point.

 

Question 24. Write the uses of Barium.
Answer: Barium and its compounds have diverse applications: 1. It is used in metallurgy, and its compounds are found in pyrotechnics (fireworks), petroleum mining, and radiology. 2. Barium acts as a deoxidizer in the refining of copper, helping to remove oxygen impurities. 3. Alloys of barium with nickel readily release electrons, making them useful in electron tubes and spark plug electrodes. 4. It functions as a scavenger, removing the last traces of oxygen and other gases in television and other electronic tubes, which improves their performance. 5. The isotope barium \( ^{133}Ba \) is used as a source for calibrating gamma-ray detectors in nuclear chemistry, ensuring accurate measurements.In simple words: Barium is used in fireworks, to clean copper, in electronics like spark plugs, and its isotope helps set up gamma-ray detectors.

🎯 Exam Tip: For barium, highlight its role in electronics and its use as a deoxidizer. Mentioning its radioactive isotope for calibration adds detail.

 

Question 25. How does beryllium hydride can be prepared?
Answer: Most elements, except beryllium, combine with hydrogen when heated to form hydrides with the general formula \( MH_2 \). Beryllium hydride (\( BeH_2 \)) cannot be made this way. Instead, \( BeH_2 \) is prepared by reacting beryllium chloride (\( BeCl_2 \)) with lithium aluminium hydride (\( LiAlH_4 \)). This is a reduction reaction where beryllium gets bonded to hydrogen. The balanced chemical equation for this preparation is:
\( 2BeCl_2 + LiAlH_4 \rightarrow 2BeH_2 + LiCl + AlCl_3 \)In simple words: Beryllium hydride is made by mixing beryllium chloride with lithium aluminium hydride, not by directly heating beryllium with hydrogen.

🎯 Exam Tip: Remember that beryllium is an exception to the general method of hydride formation. Always provide the chemical equation when asked for preparation methods.

 

Question 26. Why does solubility of sulphates of alkaline earth metal decreases? Explain.
Answer: The sulphates of alkaline earth metals are white solids that are stable to heat. Beryllium sulphate (\( BeSO_4 \)) and magnesium sulphate (\( MgSO_4 \)) dissolve easily in water, but the solubility decreases as you go down the group from calcium sulphate (\( CaSO_4 \)) to barium sulphate (\( BaSO_4 \)). This trend happens because, for \( Be^{2+} \) and \( Mg^{2+} \) ions, their higher hydration enthalpies (energy released when ions dissolve in water) are greater than their lattice enthalpy (energy holding the crystal together). This difference allows their sulphates to dissolve in water. However, for larger ions further down the group, the hydration enthalpy decreases more significantly, making the lattice stronger relatively, which reduces solubility.In simple words: Sulphates of light alkaline earth metals dissolve well because water molecules attract them strongly. But for heavier metals, this attraction to water is weaker, making their sulphates less soluble.

🎯 Exam Tip: The key to explaining solubility trends in this context is to compare hydration enthalpy and lattice enthalpy. Understand which one dominates for smaller ions versus larger ions.

 

Question 27. Write notes on plaster of paris.
Answer: Plaster of Paris is a hemihydrate of calcium sulphate (\( CaSO_4 \cdot \frac{1}{2}H_2O \)). It is made by heating gypsum (\( CaSO_4 \cdot 2H_2O \)) to about 393 K. The reaction is:
\( 2CaSO_4 \cdot 2H_2O_{(s)} \rightarrow 2CaSO_4 \cdot \frac{1}{2}H_2O + 3H_2O \) If gypsum is heated above 393 K, all the water of crystallization is lost, forming anhydrous calcium sulphate, which is known as 'dead burnt plaster'. Plaster of Paris has a special property: when mixed with an adequate amount of water, it forms a plastic mass that hardens into a solid in 5 to 15 minutes. This setting property makes it very useful. Uses: The main use of Plaster of Paris is in the building industry for plasters. It is also used to immobilize fractured bones or sprains, helping them heal. Dentists use it for casts, and it's also used in ornamental work and for making statues and busts.In simple words: Plaster of Paris is a powder made from gypsum that hardens quickly when mixed with water. It is widely used in construction, for fixing broken bones, by dentists, and for making art.

🎯 Exam Tip: Remember the chemical formula and the temperature for its preparation. Emphasize its 'setting' property and list at least three diverse uses for full marks.

 

III. Short question and answers (3 Marks):

 

Question 1. Write notes characteristic flame colouration of alkali metal salts.
Answer: When alkali metal salts are moistened with concentrated hydrochloric acid and heated on a platinum wire in a flame, they produce unique colored flames. This happens because the heat from the flame excites the valence electrons of the metal atoms to a higher energy level. When these excited electrons fall back to their original energy level, they release the extra energy as light. This light has a specific wavelength that falls in the visible region, creating a characteristic color for each metal. For example:

In simple words: Alkali metals show special colors when heated in a flame. This happens because their electrons get excited and then release light of a specific color when they return to normal.

🎯 Exam Tip: Explain the mechanism (excitation and emission of light) and provide at least three examples of alkali metals and their corresponding flame colors.

 

Question 2. Discuss the reaction of alkali metals with liquid ammonia.
Answer: Alkali metals dissolve in liquid ammonia to form deep blue solutions that conduct electricity. These solutions are similar in conductivity to pure metals. This occurs because the alkali metal atom easily loses its valence electron in the ammonia solution. Both the metal cation and the electron get surrounded by ammonia molecules, forming ammoniated cation and ammoniated electron. The general reaction is:
\( M + (x + y)NH_3 \rightarrow [M(NH_3)_x]^+ + [e(NH_3)_y]^- \) The deep blue color of the solution comes from the ammoniated electron, which absorbs energy from the visible light spectrum. These solutions are paramagnetic (attracted to a magnetic field). If left to stand, they slowly release hydrogen gas, forming an amide. The reaction to form amide is:
\( M^+ + e^- + NH_3 \rightarrow MNH_2 + \frac{1}{2}H_2 \) In a concentrated solution, the blue color changes to a bronze color, and the solution becomes diamagnetic (not attracted to a magnetic field).In simple words: Alkali metals dissolve in liquid ammonia to make a deep blue solution that conducts electricity. The blue color comes from electrons surrounded by ammonia. Over time, these solutions can change color and produce hydrogen gas.

🎯 Exam Tip: Highlight the deep blue color, electrical conductivity, and the formation of ammoniated electrons and cations. Mention the color change to bronze in concentrated solutions and amide formation.

 

Question 3. Write the properties of oxides and peroxides of alkali metals.
Answer: The oxides and peroxides of alkali metals are colorless when completely pure. However, superoxides often appear yellow or orange. Peroxides are diamagnetic, meaning they are not attracted by a magnetic field, while superoxides are paramagnetic, meaning they are attracted by a magnetic field. Sodium peroxide is commonly used as an oxidizing agent. Alkali metal hydroxides, which are formed when oxides react with water, are all white crystalline solids. These hydroxides are strong bases. They dissolve in water, releasing a lot of heat due to intense hydration.In simple words: Alkali metal oxides and peroxides are usually colorless, but superoxides are colored. Peroxides are non-magnetic, while superoxides are magnetic. All hydroxides are strong bases that dissolve in water, giving off heat.

🎯 Exam Tip: Distinguish between oxides, peroxides, and superoxides in terms of color and magnetic properties. Also, state the basic nature of their hydroxides.

 

Question 4. Write the uses of sodium carbonate.
Answer: Sodium carbonate, also known as washing soda, has several important uses: 1. It is widely used for laundering clothes and in cleaning products. 2. It serves as an important laboratory reagent for qualitative and volumetric analysis, helping chemists identify and measure substances. 3. Sodium carbonate is used in water treatment to convert hard water into soft water, by removing minerals that cause hardness. 4. It is used in various manufacturing industries, including the production of glass, paper, and paint.In simple words: Sodium carbonate is used for washing, in lab tests, to soften water, and in making glass, paper, and paint.

🎯 Exam Tip: Remember its common name 'washing soda' and list at least three distinct applications, emphasizing its role in cleaning, laboratory, and industrial processes.

 

Question 5. Write the uses of sodium hydroxide.
Answer: Sodium hydroxide, commonly known as caustic soda, is a versatile chemical with many uses: 1. It is widely used as a laboratory reagent in many chemical experiments and analyses. 2. It plays a crucial role in the purification of bauxite, which is the main ore for aluminum, and in petroleum refining processes. 3. In the textile industry, sodium hydroxide is used for mercerizing cotton fabrics, which makes them stronger and gives them a lustrous finish. 4. It is a key ingredient in the manufacture of soap, paper, artificial silk, and various other chemicals.In simple words: Sodium hydroxide is used in labs, to refine aluminum and oil, to make cotton fabric better, and to produce soap, paper, and artificial silk.

🎯 Exam Tip: List at least three applications, focusing on its use in chemical synthesis, industrial processes, and textile treatment.

 

Question 6. What are the mineral sources of alkali metals?
Answer: The primary mineral sources for alkali metals and some alkaline earth metals are:

These minerals are found in various geological formations around the world and are crucial for extracting these elements.In simple words: Different alkali and alkaline earth metals are found in specific minerals, like beryllium in beryl or magnesium in carnallite.

🎯 Exam Tip: For each element, know at least one primary mineral source and its chemical formula if applicable.

 

Question 7. Comapare the ionization energy of alkali metals with alkaline earth metals.
Answer: The ionization enthalpy is the energy needed to remove an electron from an atom. For alkaline earth metals (Group 2), the first ionization enthalpy (\( IE_1 \)) is higher than that of alkali metals (Group 1) in the same period. This is because alkaline earth metals are smaller in size and have a stronger attraction between their electrons and the nucleus. However, the second ionization enthalpy (\( IE_2 \)) for alkaline earth metals is much smaller than for alkali metals. This is because, after losing one electron, an alkali metal cation already has a stable noble gas electron configuration, making it very hard to remove a second electron. In contrast, after an alkaline earth metal loses one electron, it forms a monovalent cation with one electron still in its outermost shell, which is easier to remove than the second electron from an alkali metal. Thus, alkaline earth metals are less electropositive than alkali metals.In simple words: It takes more energy to remove the first electron from alkaline earth metals than from alkali metals. But it's easier to remove the second electron from an alkaline earth metal than from an alkali metal, because alkali metals become very stable after losing one electron.

🎯 Exam Tip: Focus on comparing \( IE_1 \) and \( IE_2 \) for both groups. Explain the stability of the noble gas configuration for alkali metals after losing one electron as the key reason.

 

Question 8. Write the uses of magnesium.
Answer: Magnesium is a widely used element with several applications: 1. It is used to remove sulfur from iron and steel, which improves their quality. 2. Magnesium is essential in the 'Kroll' process for refining titanium. 3. It is used to make photoengrave plates in the printing industry. 4. Magnesium alloys, known for being light and strong, are used in building aeroplanes and missiles. 5. Magnesium ribbon is used in organic synthesis, specifically in the preparation of Grignard reagents. 6. When alloyed with aluminium, magnesium improves the mechanical properties, ease of fabrication, and welding capabilities of the alloy. 7. Magnesium can act as a desiccant, absorbing moisture. 8. It is used as a sacrificial anode to control galvanic corrosion, protecting other metals from rust.In simple words: Magnesium is used to clean steel, make titanium, print, build planes, and help in chemical reactions. It also protects other metals from rust.

🎯 Exam Tip: Group the uses by category (e.g., metallurgy, alloys, organic chemistry) to make them easier to recall. Aim for at least four distinct applications.

 

Question 9. Write the uses of calcium.
Answer: Calcium has various important applications: 1. It serves as a reducing agent in the metallurgy of uranium, zirconium, and thorium, helping to extract these metals from their compounds. 2. Calcium is used as a deoxidizer, desulphuriser, or decarboniser for various ferrous and non-ferrous alloys, improving their purity. 3. It is a key component in making cement and mortar, which are essential building materials. 4. Calcium acts as a getter in vacuum tubes, removing residual gases to maintain the vacuum. 5. It is used in dehydrating oils, helping to remove water content. 6. Calcium compounds are used in fertilizers, concrete, and plaster of Paris.In simple words: Calcium helps make other metals, builds cement, cleans alloys, and is used in things like fertilizers and plaster.

🎯 Exam Tip: Focus on its roles as a reducing agent, in construction materials, and in purification processes. Link its uses to its chemical properties.

 

Question 10. Give uses of magnesium.
Answer: Magnesium is a widely used element with several applications: 1. It is used to remove sulfur from iron and steel, which improves their quality. 2. Magnesium is essential in the "Kroll" process for refining titanium. 3. It is used to make photoengrave plates in the printing industry. 4. Magnesium alloys, known for being light and strong, are used in building aeroplanes and missiles. 5. Magnesium ribbon is used in organic synthesis, specifically in the preparation of Grignard reagents. 6. When alloyed with aluminium, magnesium improves the mechanical properties, ease of fabrication, and welding capabilities of the alloy. 7. Magnesium can act as a desiccant, absorbing moisture. 8. It is used as a sacrificial anode to control galvanic corrosion, protecting other metals from rust.In simple words: Magnesium is used to clean steel, make titanium, print, build planes, and help in chemical reactions. It also protects other metals from rust.

🎯 Exam Tip: Group the uses by category (e.g., metallurgy, alloys, organic chemistry) to make them easier to recall. Aim for at least four distinct applications.

 

Question 11. Give the structure of \( BeCl_2 \) in the solid phase and Vapor phase.
Answer: Beryllium chloride (\( BeCl_2 \)) shows different structures depending on its state. In the solid-state, \( BeCl_2 \) forms a chain structure, where each beryllium atom is bonded to four chlorine atoms, with chlorine atoms acting as bridges between beryllium atoms.
The solid phase structure looks like this:

In the vapor phase, \( BeCl_2 \) primarily forms a chloro-bridged dimer (two \( BeCl_2 \) units linked together) at lower temperatures. This dimer has a bent structure.
The vapor phase dimer structure looks like this:

At very high temperatures (around 1200 K), the dimer breaks down into a linear monomer (\( Cl-Be-Cl \)).In simple words: Beryllium chloride is a long chain in its solid form. When it becomes a vapor, it forms a double-unit structure (dimer), and at very high heat, it turns into single straight units.

🎯 Exam Tip: Remember the keywords: 'polymeric chain' for solid, 'chloro-bridged dimer' for vapor, and 'linear monomer' for high-temperature vapor. Draw simple representations for clarity.

 

IV. Long Answer Questions(5 Marks):

 

Question 1. Compare the properties of Lithium with other elements of the group.
Answer: Lithium shows unique properties compared to other alkali metals in Group 1 due to its very small size, high polarizing power, high hydration energy, and the absence of d-orbitals. This leads to distinct chemical and physical behaviors.

These differences make lithium behave more like magnesium from Group 2 (diagonal relationship) than its own group members.In simple words: Lithium is different from other alkali metals because it is very small. It is harder, reacts less, and forms different compounds, like reacting with nitrogen directly, unlike the rest of its group.

🎯 Exam Tip: Focus on the reasons for anomalous behavior (small size, high polarizing power). Present the comparison clearly in a table format, listing at least five distinct property differences.

 

Question 2. Discuss the diagonal relationship between Lithium and Magnesium.
Answer: Lithium (Li), the first element in Group 1, shows similarities with magnesium (Mg), the second element in Group 2, which is placed diagonally to it in the periodic table. This is called a diagonal relationship. It happens because both Li and Mg have similar sizes (Li+ ion radius = 0.766 Å, Mg2+ ion radius = 0.72 Å) and similar electronegativity values (Li = 1.0, Mg = 1.2). Here are some similarities between Lithium and Magnesium: 1. Both lithium and magnesium are harder than other elements in their respective groups. 2. They both react slowly with water. Their oxides and hydroxides are much less soluble in water, and their hydroxides break down when heated. 3. Both elements form nitrides, \( Li_3N \) and \( Mg_3N_2 \), by directly reacting with nitrogen gas. 4. Neither lithium nor magnesium forms superoxides. They only form oxides (\( Li_2O \) and \( MgO \)). 5. Their carbonates (\( Li_2CO_3 \) and \( MgCO_3 \)) decompose when heated to produce their respective oxides and carbon dioxide. 6. Both lithium and magnesium do not form bicarbonates in the solid state. 7. Both lithium chloride (\( LiCl \)) and magnesium chloride (\( MgCl_2 \)) dissolve in ethanol and are deliquescent (absorb moisture from the air). They also crystallize from aqueous solution as hydrates (\( LiCl \cdot 2H_2O \) and \( MgCl_2 \cdot 8H_2O \)).In simple words: Lithium and magnesium act alike because they are similar in size and have similar chemical pulling power. Both are hard, react slowly with water, form nitrides, and have similar types of oxides and carbonates.

🎯 Exam Tip: Explain the basis of diagonal relationship (similar size and electronegativity). List at least five common properties or reactions for full marks, focusing on differences from their own groups.

 

Question 3. Explain the reaction of alkali metals with (i) Oxygen (ii) hydrogen (iii) halogens.
Answer: Alkali metals are highly reactive and react with oxygen, hydrogen, and halogens in specific ways: (i) Reaction with Oxygen: All alkali metals burn strongly when exposed to air or oxygen, forming oxides on their surface. Lithium forms only a monoxide (\( Li_2O \)). Sodium forms both a monoxide and a peroxide (\( Na_2O_2 \)). The heavier alkali metals (potassium, rubidium, caesium) form monoxides, peroxides, and superoxides (\( MO_2 \)). All these oxides are basic in nature. Examples:
\( 4Li_{(s)} + O_{2(g)} \rightarrow 2Li_2O_{(s)} \) (simple oxide)
\( 2Na + O_2 \rightarrow Na_2O_2 \) (peroxide)
\( M + O_2 \rightarrow MO_2 \) (where M = K, Rb, Cs; superoxide) (ii) Reaction with hydrogen: All alkali metals react with hydrogen gas at high temperatures (around 673 K, but lithium needs 1073 K) to form ionic hydrides. The reactivity of alkali metals with hydrogen decreases from lithium to caesium. Example:
\( 2M + H_2 \rightarrow 2M^+H^- \) (where M = Li, Na, K, Rb, Cs) The ionic character of these hydrides increases as you go down the group from lithium to caesium, but their stability decreases. These hydrides are strong reducing agents, and their reducing strength also increases down the group. (iii) Reaction with halogen: Alkali metals readily combine with halogens to form ionic halides (\( MX \)). The reactivity of alkali metals with halogens increases down the group because their ionization enthalpy decreases. Example:
\( 2M + X_2 \rightarrow 2MX \) (where M = Li, Na, K, Rb, Cs and X = F, Cl, Br, I)In simple words: Alkali metals burn in oxygen to form different types of oxides. They react with hydrogen to form hydrides. They also react with halogens to make ionic salts. Their reactivity often changes as you go down the group.

🎯 Exam Tip: For each reaction, state the general observation, the type of product formed, and provide at least one balanced chemical equation. Mention trends in reactivity or product type down the group.

 

Question 4. Write the uses of alkali metals.
Answer: Alkali metals have a variety of uses across different industries and applications: 1. Lithium metal is used to create useful alloys. For instance, with lead, it forms 'white metal' bearings for engines, with aluminium it makes aircraft parts, and with magnesium, it creates armor plates. Lithium is also used in thermonuclear reactions. 2. Lithium is a key component in electrochemical cells, such as batteries, due to its high energy density. 3. Lithium carbonate is used in medicines, especially for treating bipolar disorder. 4. Sodium is used to make \( Na/Pb \) alloy, which is needed to produce tetraethyl lead (\( Pb(Et)_4 \)) and tetramethyl lead (\( Pb(Me)_4 \)). These organolead compounds were previously used as anti-knock additives in petrol. 5. Liquid sodium metal is used as a coolant in fast breeder nuclear reactors because it efficiently transfers heat. 6. Potassium plays a vital role in biological systems, being essential for nerve function and fluid balance. 7. Potassium chloride is used as a fertilizer to provide essential nutrients to plants. Potassium hydroxide is used to make soft soap. It also acts as an excellent absorbent for carbon dioxide. 8. Caesium is used in the development of photoelectric cells, which convert light into electricity, due to its low ionization energy.In simple words: Alkali metals like lithium, sodium, potassium, and caesium are used in many ways: to make special alloys, in batteries, in medicine, as coolants in reactors, in fertilizers, to make soap, and in devices that turn light into power.

🎯 Exam Tip: List at least two uses for each of the main alkali metals (Li, Na, K, Cs) if possible, linking the use to a specific property or application.

 

Question 5. How is washing soda prepared? Discuss its properties.
Answer: Sodium carbonate (\( Na_2CO_3 \)), commonly known as washing soda, is an important inorganic compound primarily prepared by the Solvay process. Preparation (Solvay Process): In this process, ammonia is first converted into ammonium carbonate, which then reacts with carbon dioxide to form ammonium bicarbonate. Excess carbon dioxide is passed through a sodium chloride solution saturated with ammonia. 1. Formation of ammonium carbonate:
\( 2NH_3 + H_2O + CO_2 \rightarrow (NH_4)_2CO_3 \) 2. Formation of ammonium bicarbonate:
\( (NH_4)_2CO_3 + H_2O + CO_2 \rightarrow 2NH_4HCO_3 \) The ammonium bicarbonate then reacts with sodium chloride to produce sodium bicarbonate and ammonium chloride. Since sodium bicarbonate has low solubility, it precipitates out. 3. Precipitation of sodium bicarbonate:
\( 2NH_4HCO_3 + NaCl \rightarrow NH_4Cl + NaHCO_3 \) The precipitated sodium bicarbonate is then isolated and heated to yield sodium carbonate. 4. Formation of sodium carbonate:
\( 2NaHCO_3 \rightarrow Na_2CO_3 + CO_2 + H_2O \) The ammonia used in the process can be recovered by treating the resulting ammonium chloride solution with calcium hydroxide. Calcium chloride is formed as a by-product. Properties of Washing Soda: Sodium carbonate crystallizes as a decahydrate (\( Na_2CO_3 \cdot 10H_2O \)), which is a white powder. It is readily soluble in water and forms an alkaline solution. When heated, it loses its water of crystallization to form monohydrate (\( Na_2CO_3 \cdot H_2O \)). Above 373 K, the monohydrate loses all its water and becomes completely anhydrous, known as soda ash (\( Na_2CO_3 \)). Heating reactions:
\( Na_2CO_3 \cdot 10H_2O \rightarrow Na_2CO_3 \cdot H_2O + 9H_2O \)
\( Na_2CO_3 \cdot H_2O \rightarrow Na_2CO_3 + H_2O \)In simple words: Washing soda is made using the Solvay process, which involves several steps using ammonia, carbon dioxide, and salt. It's a white powder that dissolves in water to make an alkaline solution and loses its water when heated.

🎯 Exam Tip: Detail the Solvay process steps with balanced equations. Describe its physical appearance, solubility, and behavior on heating, including the term 'soda ash'.

 

Question 6. Compare the properties of Beryllium with other elements of the group.
Answer: Beryllium, the first element of Group 2 (alkaline earth metals), shows significant differences from the other elements in its group due to its small size, high charge density, and high electronegativity.

These distinct properties of beryllium highlight its anomalous behavior compared to its heavier congeners.In simple words: Beryllium is unique in its group. It forms covalent bonds, has high melting points, and does not react with water or hydrogen easily, unlike other alkaline earth metals. Its oxides are also different, acting as both acid and base.

🎯 Exam Tip: The key is to present a clear table comparing beryllium's properties (covalent character, reactivity, amphoteric nature) with the typical behavior of other Group 2 elements. Emphasize its small size as the root cause.

 

Question 7. Explain the diagonal relationship of Beryllium with Aluminium.
Answer: Beryllium, which is the first element in Group 2, shows a diagonal relationship with aluminum. This happens because they have similar characteristics, even though they are in different groups and periods. While their ionic sizes (for \( \text{Be}^{2+} \) at 0.45 Å and \( \text{Al}^{3+} \) at 0.54 Å) are not very close, their charge per unit area is quite similar (\( \text{Be}^{2+} \) = 2.36 and \( \text{Al}^{3+} \) = 2.50). They also share similar electronegativity values (Be = 1.5; Al = 1.5). This similarity leads to some shared chemical properties between them.
**Properties:**
1. Beryllium chloride forms a twin structure (dimer) with chloride bridges, just like aluminum chloride. It also forms a chain-like structure (polymeric). Both are strong Lewis acids and can dissolve in organic solvents.
2. Beryllium hydroxide dissolves in strong alkaline solutions, forming beryllate ion \( (\text{[Be(OH)}_{4}\text{]}^{2-}) \). Similarly, aluminum hydroxide forms aluminate ion \( (\text{[Al(OH)}_{4}\text{]}^{-}) \).
3. Both beryllium and aluminum ions are good at forming complex compounds, such as \( \text{BeF}_{4}^{2-} \) and \( \text{AlF}_{6}^{3-} \).
4. The hydroxides of both beryllium and aluminum are amphoteric, meaning they can act as both acids and bases.
5. Carbides of beryllium \( (\text{Be}_{2}\text{C}) \) react with water to produce methane gas, similar to aluminum carbide \( (\text{Al}_{4}\text{C}_{3}) \).
6. Both beryllium and aluminum become passive when treated with nitric acid, forming a protective layer that stops further reaction.
In simple words: Beryllium and aluminum are like chemical cousins, sharing many properties because their small size and charge density are very similar. They behave alike in many reactions, forming similar types of compounds.

🎯 Exam Tip: When discussing diagonal relationships, always highlight the similarities in ionic size, charge density, and electronegativity as the primary reasons for shared properties.

 

Question 8. Explain the properties and uses of Gypsum.
Answer:
**Properties of Gypsum:**
1. Gypsum is a soft mineral that dissolves moderately in water. Its unique "retrograde solubility" means it becomes less soluble as temperature rises, which is unusual for most salts.
2. Gypsum is typically white, colorless, or gray. However, impurities can give it shades of pink, yellow, brown, or light green.
3. Gypsum crystals can form in shapes resembling flower petals, known as 'desert rose' formations, which are common in dry areas.
4. It has low thermal conductivity, making it a natural insulator often used in drywall and wallboards.
5. Alabaster, a valuable variety of gypsum, is an opaque, granular stone highly prized for ornamental work and has been used by sculptors for centuries.
6. Gypsum's hardness is between 1.5 and 2 on the Moh's scale, and its specific gravity ranges from 2.3 to 2.4.
**Uses of Gypsum:**
1. Ancient Egyptians and Mesopotamians used alabaster for sculptures, discovering how to convert gypsum into plaster of Paris around 5,000 years ago. Today, gypsum has many applications.
2. It is widely used in the construction industry for making drywalls, plasterboards, and as a finish for walls, ceilings, and partitions.
3. A key use of gypsum is in producing plaster of Paris. When heated to about 300 degrees Fahrenheit, it forms plaster of Paris, also called gypsum plaster, primarily used for sculpting.
4. It is essential for medical applications, such as creating surgical and orthopedic casts for broken bones and sprains.
5. In agriculture, gypsum acts as a soil additive, conditioner, and fertilizer. It helps loosen compact clay soil, provides calcium and sulfur vital for plant growth, and can remove excess sodium from saline soils.
In simple words: Gypsum is a soft mineral that is not very soluble in water. It is used a lot in construction for walls and ceilings, in medicine for casts, and in farming to help soil and plants grow better.

🎯 Exam Tip: When describing properties and uses, categorize them clearly (e.g., physical properties, chemical properties, industrial uses, medical uses) to show a comprehensive understanding.

 

Question 9. Mention the biological importance of sodium and potassium.
Answer:
**Biological Importance of Sodium and Potassium:**
Both sodium \( (\text{Na}^{+}) \) and potassium \( (\text{K}^{+}) \) ions are crucial for life and are found in large amounts in biological fluids. They perform several vital functions that keep the body working correctly.
**Sodium:**
1. Sodium ions are mainly found outside cells, specifically in blood plasma and the interstitial fluid that surrounds cells.
2. They are key to transmitting nerve signals, helping regulate water balance across cell membranes, and transporting sugars and amino acids into cells.
3. A typical 70 kg person has about 90 grams of sodium.
**Potassium:**
1. Potassium ions are the most common positive ions inside cells.
2. They help activate many enzymes and are involved in converting glucose into ATP (energy). Along with sodium, they are essential for sending nerve signals.
3. A typical 70 kg person contains approximately 170 grams of potassium, showing its higher intracellular concentration compared to sodium.
**Combined Role:**
Both ions work together, especially in the sodium-potassium pump, which is crucial for nerve signal transmission and maintaining electrolyte balance in the body. While chemically similar, they differ in how they move across cell membranes and their roles in enzyme activation.
In simple words: Sodium and potassium are vital chemicals in our bodies. Sodium mostly works outside cells to help nerves send messages and keep water balanced. Potassium works inside cells to give us energy and help enzymes. Together, they make sure our nerves and muscles function correctly.

🎯 Exam Tip: Remember to differentiate between the primary locations of sodium (outside cells) and potassium (inside cells) and their specific roles to score full marks.