Selina Concise Solutions for ICSE Class 10 Chemistry Chapter 7 Metallurgy

Exercise 7(A)

Question 1. Name the three classes in which elements are classified. Which was the first metal used by man?
Answer: Three classes in which elements are classified are: Metals, Non-metals and Metalloids. Copper was the first metal used by man.
In simple words: All elements in nature are divided into three main groups - metals (like iron, gold), non-metals (like oxygen, carbon), and metalloids (like silicon). Ancient humans first discovered how to use copper for making tools.

📝 Teacher's Note: Show students examples of each class - a coin (metal), a pencil lead (non-metal), and computer chip (metalloid). Explain that copper was chosen first because it's easily found in pure form and soft enough to shape.

🎯 Exam Tip: Remember the three classes clearly and always mention that copper was the first metal - this is a frequently asked fact in exams.

Question 2. Name the metal which is a constituent of: (a) Blood pigment, (b) plant pigment
Answer: (a) The metal which is a constituent of blood pigment is Iron (Fe). (b) The metal which is a constituent of plant pigment is Magnesium (Mg).
In simple words: Iron makes our blood red and helps carry oxygen around our body. Magnesium makes plants green and helps them make food from sunlight.

📝 Teacher's Note: Connect this to students' daily life - iron deficiency causes anemia (pale skin), and chlorophyll (green color) in plants contains magnesium. Use visual aids showing red blood cells and green leaves.

🎯 Exam Tip: Associate iron with blood (hemoglobin) and magnesium with plants (chlorophyll) - these are direct one-word answers that examiners expect.

Question 3. Give the importance of the following in living beings: (a) Nitrogen, (b) Hydrogen, (c) carbon
Answer: (a) Nitrogen: It is used to preserve food. (b) Hydrogen: It is used in the hydrogenation of vegetable oils to make ghee. (c) Carbon: It is essential for the growth and development of living beings.
In simple words: Nitrogen helps keep food fresh for longer time. Hydrogen is used to change liquid oil into solid ghee or butter. Carbon is the building block of all living things - our body is mostly made of carbon compounds.

📝 Teacher's Note: Clarify that nitrogen in living beings mainly forms proteins and DNA, not just food preservation. Explain hydrogenation process with examples like Dalda. Emphasize carbon as the backbone of all organic molecules.

🎯 Exam Tip: For nitrogen, mention protein formation along with food preservation. For carbon, always state it's essential for life - this shows understanding beyond memorization.

Question 4. Name the metal and non-metal present in abundance in the earth crust.
Answer: The metal which is present in abundance in earth's crust is aluminium. The non-metal which is present in abundance in the earth crust is oxygen.
In simple words: Aluminium is the most common metal found in rocks and soil on Earth. Oxygen is the most common non-metal element found everywhere in air, water, and rocks.

📝 Teacher's Note: Explain that although oxygen is most abundant overall, students should understand that most oxygen is bound in compounds like water and rocks, not as free gas in atmosphere.

🎯 Exam Tip: Always specify "earth's crust" in your answer - this distinguishes from abundance in atmosphere or universe, which would have different answers.

Question 5. Define metal and non-metal on the basis of electron loss or gain.
Answer: Metals are defined as the elements which form positive ions by the loss of electrons. Non-metals are the elements which form negative ions by the gain of electrons.
In simple words: Metals easily give away electrons to become positively charged, while non-metals prefer to take electrons to become negatively charged.

📝 Teacher's Note: Use the analogy of giving and taking - metals are "generous" and give away electrons, non-metals are "greedy" and take electrons. This helps students remember the behavior.

🎯 Exam Tip: Always mention "positive ions" for metals and "negative ions" for non-metals - these specific terms earn full marks in definitions.

Question 6. State the position of the following in the periodic table: (a) Alkali metals, (b) Alkaline earth metals (c) Iron and zinc (d) Aluminium
Answer: (a) Alkali metals: They are placed in IA group, the first column on the left of the periodic table. (b) Alkaline earth metal: They are placed in IIA group, the second column on the left of the periodic table. (c) Iron and Zinc: Fe is placed in VIII group and Zn is placed in IIB group. (d) Aluminium: It is placed in IIIA group present on the right of periodic table.
In simple words: Alkali metals are in the first column, alkaline earth metals in the second column. Iron is in group 8 and zinc in group 12 (transition metals). Aluminium is in group 13.

📝 Teacher's Note: There's an error in the original answer - it says "Cu" instead of "Zn" for zinc. Use a periodic table chart to show these positions visually. Explain that group numbers help predict properties.

🎯 Exam Tip: Remember IA = alkali, IIA = alkaline earth. For transition metals like iron and zinc, mention their specific group numbers clearly.

Question 7. Give the general characteristics of: (a) Alkali metals, (b) Alkaline earth metals with reference to (i) bonding (ii) action of air (iii) action of water (iv) action of acid
Answer: (a) Alkali metals:- (i) Bonding: All alkali metal salts are ionic in nature. (ii) Action of air: They react rapidly with oxygen and water vapour in the air. (iii) Action of water: They react violently with water and produce hydrogen gas. \( 2M + 2H_2O \rightarrow 2MOH + H_2 \) (iv) Action of acid: They react violently with dil. HCl and dil. \( H_2SO_4 \) to produce hydrogen gas. \( 2M + 2HCl \rightarrow 2MCl + H_2 \) (b) Alkaline earth metal:- (i) Bonding: All alkaline earth metal salts except beryllium are ionic compounds. (ii) Action of air: They are less reactive than alkali metals. (iii) Action of water: They react with water to produce hydrogen gas. \( M + 2H_2O \rightarrow M(OH)_2 + H_2 \) (iv) Action of acid: They react with dilute HCl and dil. \( H_2SO_4 \) to produce hydrogen gas. \( M + 2HCl \rightarrow MCl_2 + H_2 \)
In simple words: Alkali metals are very reactive - they react quickly with air and water, making hydrogen gas. Alkaline earth metals are less reactive than alkali metals but still react with water and acids to produce hydrogen gas.

📝 Teacher's Note: Emphasize safety - alkali metals must be stored under oil because they react with air moisture. Demonstrate with videos if possible. Explain that reactivity decreases from alkali to alkaline earth metals.

🎯 Exam Tip: Always write balanced chemical equations for water and acid reactions. Remember that alkaline earth metals are "less reactive" than alkali metals - this comparison often appears in exams.

Question 8. What are metalloids: Give examples.
Answer: Elements which show properties of both metals and non-metals are called metalloids. For example: Silicon, Germanium.
In simple words: Metalloids are elements that act like metals sometimes and like non-metals other times - they're like a mixture of both types.

📝 Teacher's Note: Explain that metalloids are crucial in electronics - silicon in computer chips, germanium in transistors. They conduct electricity better than non-metals but not as well as metals.

🎯 Exam Tip: Always mention that metalloids have properties of "both metals and non-metals" - this definition is key for full marks.

Question 9. Why is hydrogen placed with alkali metals?
Answer: Hydrogen is placed with alkali metals as it has one electron similar to the alkali metals.
In simple words: Hydrogen has one electron in its outer shell, just like alkali metals, so it's grouped with them even though it's not a metal.

📝 Teacher's Note: Clarify that hydrogen is unique - it's placed with alkali metals due to electron configuration but behaves differently. It's a non-metal gas, not a metal.

🎯 Exam Tip: Mention "one electron in outer shell" - this is the specific reason examiners look for in this question.

Question 10. Name: (a) a liquid non-metal, (b) a metal with dull appearance (c) a metal with low melting and boiling points (d) a non-metal with high m.p & b.p (e) a metal which can float on water (f) a metal which can be cut with a knife. (g) a metal which is a bad conductor of heat and electricity (h) a non-metal which is ductile (i) a non- metal used in alloys (j) a non-malleable metal
Answer: (a) Bromine (b) Lead (c) Gallium (d) Carbon (e) Sodium (f) Sodium (g) Tungsten (h) Carbon fibre (i) Carbon (j) Mercury
In simple words: Each element has unique properties - bromine is liquid at room temperature, sodium is so light it floats on water and so soft you can cut it with a knife.

📝 Teacher's Note: There are errors in the original answers - tungsten is actually an excellent conductor. The correct answer for (g) should be lead or bismuth. Use real examples where possible to help students remember.

🎯 Exam Tip: These are factual questions - memorize the unique properties of common elements. Sodium appears twice here (floats and can be cut) - this helps you remember its properties.

Question 11. Distinguish between metals and non metals on the basis of: (i) ion formation, (ii) discharge of ions, (iii) nature of oxide formed, (iv) oxidizing and reducing property, (v) reaction with acids.
Answer: (i) Ion formation: Metals form positive ions by loss of electrons whereas non- metals form negative ions by gain of electrons. (ii) Discharge of ions: Metals are discharged at the cathode during electrolysis whereas non-metals are liberated at the anode during electrolysis. (iii) Nature of oxide formed: Oxides of metals are usually basic. Soluble basic oxides dissolve in water forming an alkaline solution whereas oxides of non-metals are usually acidic. Soluble acidic oxides dissolve in water forming an acidic solution. (iv) Oxidizing and reducing property: Metals ionize by loss of electrons and hence are reducing agents whereas non-metals ionize by gain of electrons and hence are oxidizing agents. (v) Reaction with acids: Metals above hydrogen in activity series usually replace hydrogen from dilute non-oxidising acids whereas non-metals do not react with dilute hydrochloric acid or sulphuric acid.
In simple words: Metals and non-metals behave oppositely in most chemical reactions - where metals lose electrons, non-metals gain them; where metals form basic oxides, non-metals form acidic ones.

📝 Teacher's Note: Use electrolysis apparatus to demonstrate cathode and anode discharge. Show litmus paper tests with metal and non-metal oxides to demonstrate basic vs acidic nature.

🎯 Exam Tip: This is a comparison question - always present metals vs non-metals clearly for each point. Mention specific terms like "cathode," "anode," "reducing agents," "oxidizing agents."

Question 12. (a) Na _____ → Na+ (b) N+ _____ → N3- (c) Cl +e- → _____ (d) Mg -_____ → Mg2+ (e) M+ HCl → MCl2 +_____ (f) Mg +H2SO4 → _____ + _____
Answer: (a) Na -e- → Na+ (b) N+ 3e- → N3- (c) Cl +e- → Cl- (d) Mg -2e- → Mg2+ (e) M+ 2HCl → MCl2 + H2 (f) Mg +H2SO4 → MgSO4 + H2
In simple words: These equations show how atoms lose or gain electrons to form ions, and how metals react with acids to produce hydrogen gas.

📝 Teacher's Note: Emphasize electron counting - sodium loses 1 electron, magnesium loses 2. For reactions, stress that hydrogen gas is always produced when metals react with acids.

🎯 Exam Tip: Always balance equations properly. Remember that the charge on the ion tells you how many electrons are lost or gained.

Question 13. Select from the following list: Fe2O3, NO, PbO, Mn2O7 (a) Basic oxide……….. (b) Amphoteric oxide ………… (c) Acidic oxide ……………… (d) Neutral oxide …………….
Answer: (a) Fe2O3 (b) PbO (c) Mn2O7 (d) NO
In simple words: Different metal oxides have different properties - some are basic, some can act as both acid and base (amphoteric), some are acidic, and some are neutral.

📝 Teacher's Note: Explain that metal oxidation state affects oxide nature - higher oxidation states tend to be more acidic. PbO is amphoteric because lead can show different oxidation states.

🎯 Exam Tip: Remember that most metal oxides are basic, but high oxidation state metal oxides (like Mn2O7) can be acidic. Neutral oxides like NO are uncommon.

Question 14. Take an element from an alkali metal and one from an alkaline earth metal and write an equation for their action with: (a) Hydrochloric acid, (b) Oxygen (c) Sulphuric acid (d) Water.
Answer: (a) Hydrochloric acid: \( 2Na + 2HCl \rightarrow 2NaCl + H_2 \) \( Be + 2HCl \rightarrow BeCl_2 + H_2 \) (b) Oxygen: \( 4Na + O_2 \rightarrow 2Na_2O \) \( 2Mg + O_2 \rightarrow 2MgO \) (c) Sulphuric acid: \( 2Na + H_2SO_4 \rightarrow Na_2SO_4 + H_2 \) \( Mg + H_2SO_4 \rightarrow MgSO_4 + H_2 \) (d) Water \( 2Na + 2H_2O \rightarrow 2NaOH + H_2 \) \( Mg + 2H_2O \rightarrow Mg(OH)_2 + H_2 \)
In simple words: Both alkali and alkaline earth metals react with acids to give hydrogen gas, with oxygen to form oxides, and with water to form hydroxides plus hydrogen gas.

📝 Teacher's Note: Point out the pattern - all acid reactions produce hydrogen, all oxygen reactions form oxides, all water reactions form hydroxides. The stoichiometry changes based on valency.

🎯 Exam Tip: Always balance equations correctly. Notice that alkali metals need coefficient 2 in most reactions while alkaline earth metals need coefficient 1 with acids and water.

Exercise 7(B)

Question 1. Name: (a) Two metals which are liquid at room temperature (b) two metals which are soft (c) a metal which lacks ductility (d) a non metal which is lustrous (e) a non metal which conducts electricity (f) a metal which is brittle (g) two non metals which are monoatomic (h) two metallic oxides which are acidic (i) two metallic oxides which are amphoteric
Answer: (a) Mercury and Gallium (b) Sodium and Potassium (c) Zinc (d) Iodine (e) Graphite (carbon) (f) Manganese (g) Helium and Neon (h) \( CrO_3 \) and \( Mn_2O_7 \) (i) \( Al_2O_3 \) and \( ZnO \)
In simple words: Different elements have unique properties - some metals are liquid like mercury, some non-metals shine like iodine, and some can conduct electricity like graphite in pencils.

📝 Teacher's Note: Show actual examples where possible - mercury thermometer, graphite pencil lead, iodine crystals. Explain that these exceptions help students understand that properties aren't absolute rules.

🎯 Exam Tip: These are specific factual questions. Remember unusual properties like liquid metals (mercury, gallium) and conducting non-metals (graphite) as they often appear in exams.

Question. Give one word/few words for each of the following:
(a) two metals which are in liquid state at room temperature
(b) the most reactive metals
(c) the metal which does not react with water
(d) a non-metal which is a good conductor of electricity
(e) a non-metal which can form a positive ion
(f) a metal used to galvanise iron
(g) two noble gases
(h) two acidic oxides
(i) two amphoteric oxides
(j) two metals which react with cold water
(k) the compound responsible for green deposit on the surface of copper
(l) the most abundant metal and the most abundant non-metal
(m) a non metal which can form a positive ion
(n) a non-metal which shows reducing property
(o) a metal whose oxide is reduced only by carbon
Answer:
(a) Mercury and gallium
(b) Sodium and potassium
(c) Mercury
(d) Iodine
(e) Graphite
(f) Zinc
(g) Neon, Argon
(h) \( CrO_3 \), \( Mn_2O_7 \)
(i) \( Al_2O_3 \), \( PbO \)
(j) Potassium, sodium
(k) Basic copper(II) sulphate
(l) Aluminium, Oxygen
(m) Hydrogen
(n) Carbon
(o) Iron
In simple words: These are basic facts about metals and non-metals - like which ones are liquid at room temperature, which react with water, and what compounds they form.

📝 Teacher's Note: Create flashcards for these one-word answers as they're frequently asked in exams. Use visual aids showing mercury in a thermometer and copper turning green to make it memorable.

🎯 Exam Tip: Remember "Mercury and gallium are liquid" and "Sodium and potassium react with cold water" - these are high-scoring one-mark questions that appear every year.

Question. Explain how the activity series accounts for each of the following:
(a) occurrence of metals (b) tendency to corrosion
(c) reaction with water (d) reaction with acids
Answer:
(a) Occurrence of metals: The metals placed at the top of activity series are most reactive, so they always exist in the combined state whereas the metals placed below the activity series are least reactive, so they can be found in the isolated state also.
(b) Tendency to corrosion: The metals lying above the hydrogen in activity series can easily react with moisture and air and corrode easily whereas the metals such as gold and platinum do not corrode easily.
(c) Reaction with water: The ability of the metals to reduce water to hydrogen decreases on moving down the series. Potassium and sodium reacts with cold water whereas magnesium reacts with warm water and aluminium, zinc and iron reacts with steam.
(d) Reaction with acids: All the metals above hydrogen, in the activity series, reduce hydrogen ions from dil. hydrochloric or sulphuric acid and give out hydrogen gas. The rate of reaction decreases on moving down the series.
In simple words: The activity series is like a ranking system - metals at the top are very active and react easily, while those at the bottom are calm and don't react much.

📝 Teacher's Note: Draw the activity series on the board and use it as reference throughout the chapter. Demonstrate with actual metals if possible - sodium's violent reaction vs copper's lack of reaction with water.

🎯 Exam Tip: Always mention "decreases down the series" when explaining reactivity trends. Use phrases like "above hydrogen" and "below hydrogen" to show clear understanding.

Question. Give the balanced reactions for the following:
(a) Sodium is dropped in water
(b) Magnesium reacts with boiling water
(c) Red hot iron reacts with steam
(d) Iron reacts with dilute HCI
Answer:
(a) \( 2Na + 2H_2O \rightarrow 2NaOH + H_2 \)
(b) \( Mg + H_2O \rightarrow MgO + H_2 \)
(c) \( 3Fe + 4H_2O \rightarrow Fe_3O_4 + 4H_2 \)
(d) \( Fe + 2HCl \rightarrow FeCl_2 + H_2 \)
In simple words: These reactions show how different metals react with water and acids - some need heat, others react at room temperature, but all produce hydrogen gas.

📝 Teacher's Note: Emphasize the pattern - metals above hydrogen in activity series displace hydrogen from water/acids. Show students how to balance equations step by step.

🎯 Exam Tip: Remember that hydrogen gas is always produced when metals react with acids or water. Check your balanced equations by counting atoms on both sides.

Question. Give a short account of heating effect on metal carbonates based on the activity series.
Answer: The metals placed higher in the activity series (i.e. Na and K) are stable to heat and soluble in water. Whereas metals like Ca, Mg, Al, Zn, Fe, Pb, Cu decompose on heating with decreasing vigour to form metal oxide and carbon dioxide. The metals which lie below in the activity series (i.e. Hg, Ag) decompose on heating to form metal, oxygen and carbon dioxide.
In simple words: Very reactive metals' carbonates don't break when heated, moderately reactive metals' carbonates break to give oxide and CO₂, while least reactive metals' carbonates completely break down.

📝 Teacher's Note: Use the analogy of friendship strength - strong friendships (highly reactive metals) don't break easily with pressure (heat), while weak ones do.

🎯 Exam Tip: Write the three categories clearly: stable to heat, decompose to oxide + CO₂, decompose to metal + O₂ + CO₂. This systematic approach ensures full marks.

Question.
(a) Why are alkali metals kept in kerosene oil?
(b) What is:
(i) basic lead carbonate and
(ii) brown powder deposit on iron?
(c) Why is hydrogen kept in the metal activity series?
Answer:
(a) Alkali metals like sodium and potassium are kept in kerosene as they react with moisture and air.
(b)
(i) Basic lead carbonate is a mixture of lead hydroxide and lead carbonate.
(ii) Brown powder is mainly hydrated iron(III) oxide \( (Fe_2O_3.xH_2O) \)
(c) Hydrogen is kept in the metal activity series because it helps us compare the reactivity of metals. Metals above hydrogen can displace it from acids, while metals below cannot.
In simple words: Alkali metals are so reactive they need oil protection, lead carbonate is a mixture compound, brown powder is rust, and hydrogen acts as a reference point in the activity series.

📝 Teacher's Note: Show students actual kerosene-stored sodium if available. Explain that hydrogen isn't a metal but serves as a useful reference point for comparison.

🎯 Exam Tip: For part (c), always mention that hydrogen is a reference point for displacement reactions. This shows deeper understanding of the activity series concept.

Question. Give the effect of heat on metal oxides based on the activity series.
Answer: Oxides of metals like Na, K, Ca, Mg, Al are stable to heat and so can be reduced only by electrolysis. Zinc oxide can be reduced by coke only. Oxides of iron, lead and copper are reduced by C, CO, H₂ and NH₃. Oxides of mercury and silver decompose to give metal and oxygen.
In simple words: The more reactive a metal, the more stable its oxide is to heat - very reactive metals' oxides need electricity to break them, while unreactive metals' oxides break easily with just heating.

📝 Teacher's Note: Connect this to extraction of metals - why we need electrolysis for aluminum but simple heating works for mercury. Use industrial examples.

🎯 Exam Tip: Categorize oxides into four groups based on reduction methods: electrolysis only, carbon reduction, multiple reducing agents, thermal decomposition.

Question. Metal A has an electronic configuration of 2, 8, 1 and metal B has 2, 8, 8, 2 which is more reactive metal.
(a) Identify A and B and give their reactions with dil HCL and dil H₂SO₄
(b) Give the effect of heat on their:
(i) oxides (ii) hydroxide (iii) carbonates (iv) nitrates
Answer: Metal A is more reactive than Metal B.
(a) Metal A is Na (Sodium). Metal B is Ca (Calcium).
Reaction with HCl:
\( 2Na + 2HCl \rightarrow 2NaCl + H_2 \)
\( Ca + 2HCl \rightarrow CaCl_2 + H_2 \)
Reaction with H₂SO₄:
\( 2Na + H_2SO_4 \rightarrow Na_2SO_4 + H_2 \)
\( Ca + H_2SO_4 \rightarrow CaSO_4 + H_2 \)
(b)
(i) Oxides: Sodium and calcium oxides are stable to heat.
(ii) Hydroxides: Sodium hydroxide is stable to heat whereas calcium hydroxide decomposes on heating to metal oxide and water vapour.
(iii) Carbonates: Sodium carbonate is stable to heat whereas calcium carbonates decompose on heating to form calcium oxide and carbon dioxide.
(iv) Nitrates: Sodium nitrate on heating form nitrite and oxygen whereas calcium nitrate decomposes on heating to form calcium oxide, nitrogen dioxide and oxygen.
In simple words: Sodium (2,8,1) is more reactive than calcium (2,8,8,2) because it loses electrons more easily. Their compounds behave differently when heated.

📝 Teacher's Note: Emphasize how electronic configuration determines reactivity - fewer valence electrons mean easier to lose and higher reactivity. Use periodic table trends.

🎯 Exam Tip: Always identify metals first using electronic configuration, then write balanced equations. Remember sodium compounds are generally more stable to heat than calcium compounds.

Question.
(a) The table below compares some properties of metals and non-metals. Write down the missing statements (i) to (iv):

(b) How many valence electrons are present in:
(i) metals and (ii) non-metals?
Answer:
(a)

(b) Valence electrons present in:
(i) Metals have 1, 2 or 3 valence electrons.
(ii) Non-metals have 5, 6 or 7 valence electrons.
In simple words: Metals and non-metals are opposite in most properties - metals conduct, stretch, form positive ions and basic oxides, while non-metals do the reverse.

📝 Teacher's Note: Create a comparison chart on the board. Use examples like aluminum foil (malleable metal) vs sulfur powder (brittle non-metal) to demonstrate properties.

🎯 Exam Tip: Remember the pattern: metals have 1-3 valence electrons (lose to form positive ions), non-metals have 5-7 valence electrons (gain to form negative ions).

Question. What is corrosion? What are necessary conditions for corrosion?
Answer: When the surface of metal is attacked by air, moisture or any other substance around it, the metal is said to corrode and the phenomenon is known as corrosion. Necessary conditions for corrosion are: 1. Presence of oxygen and moisture. 2. Metals which are placed higher in the activity series corrode more easily.
In simple words: Corrosion is like metals getting sick when exposed to air and water - more reactive metals get sick faster than less reactive ones.

📝 Teacher's Note: Show rusted iron objects and compare with shiny aluminum. Explain why ships need special coatings and why gold jewelry doesn't corrode.

🎯 Exam Tip: Always mention both oxygen AND moisture as necessary conditions. Don't forget to link corrosion rate to the activity series position.

Question. State under what conditions corrosion is faster
Answer: Conditions for increase of corrosion are: 1. Presence of oxygen and moisture. 2. Metals which are placed higher in activity series corrode more easily 3. Dissolved salts in water act as electrolyte and enhance the rate of corrosion. 4. The presence of pollutants like NO₂ and CO₂ increases rusting.
In simple words: Corrosion happens faster in salty, polluted, humid environments - like how cars rust faster near the ocean or in polluted cities.

📝 Teacher's Note: Discuss real-life examples: coastal areas, industrial pollution, road salt in winter. Connect to students' observations of rust patterns.

🎯 Exam Tip: List all four conditions systematically. Mentioning pollutants shows advanced understanding and can earn extra marks.

Question. Corrosion can be an advantage in some case.Explain
Answer: Corrosion of metals is an advantage as it prevents the metal underneath from further damage. For example: On exposure to air, the surface of metal like aluminium and Zinc forms layers of their oxides which are very sticky and impervious in nature and hence act as protective layer. This layer protects the metal from further damage.
In simple words: Sometimes corrosion is helpful because it creates a protective skin on metals like aluminum, just like how a scab protects a wound from getting worse.

📝 Teacher's Note: Show aluminum foil and explain the thin oxide layer. Compare with iron rusting which flakes off vs aluminum oxide which sticks and protects.

🎯 Exam Tip: Use terms like "protective layer," "impervious," and "prevents further damage." Give specific examples of aluminum and zinc for full marks.

Question. What is rust? Give the equation for the formation of rust.
Answer: Rusting is the slow oxidation of iron by atmospheric oxygen in the presence of water. Equation: \( 4Fe + 3O_2 + 2xH_2O \rightarrow 2Fe_2O_3.xH_2O \)
In simple words: Rust is what happens when iron slowly combines with oxygen and water from air to form a reddish-brown compound that weakens the iron.

📝 Teacher's Note: Emphasize that rusting is specific to iron, while corrosion is general for all metals. Show the hydrated nature of rust (x can vary).

🎯 Exam Tip: Remember rust is hydrated iron oxide. The equation shows both oxygen and water are needed, and the 'x' indicates variable water content.

Question. State two conditions necessary for rusting of iron.
Answer: Two conditions necessary for rusting of iron are: 1. Air 2. Water
In simple words: Iron needs both air (oxygen) and water to rust - remove either one and rusting stops completely.

📝 Teacher's Note: Demonstrate with three test tubes: iron in air only, iron in water only, iron in both - only the third one rusts.

🎯 Exam Tip: Simple and direct answer - just "Air" and "Water." Don't overcomplicate this basic question.

Question. How does the painting of an iron object prevent rusting?
Answer: By painting an iron object, the iron do not come in contact with atmospheric reagents. This prevents rusting.
In simple words: Paint acts like a protective coat that keeps air and water away from iron, just like an umbrella keeps rain away from you.

📝 Teacher's Note: Explain why car paint chips lead to rust spots. Discuss how scratches in paint expose iron to air and moisture.

🎯 Exam Tip: Key phrase is "prevents contact with atmospheric reagents." This shows you understand the mechanism of prevention.

Question. What is galvanization? How does it protect iron from rusting?
Answer: Galvanisation is the process of applying a protective zinc coating to steel or iron, in order to prevent rusting. The zinc coating does not allow iron to come in contact with air and moisture and thus protects it from rusting.
In simple words: Galvanization is like putting a zinc jacket on iron - the zinc takes the hit from air and water instead of the iron underneath.

📝 Teacher's Note: Show galvanized iron sheets and explain how zinc corrodes preferentially. Discuss why zinc is chosen over other metals for this purpose.

🎯 Exam Tip: Mention both the definition of galvanization and the protection mechanism. Zinc's position in activity series makes it sacrifice itself to protect iron.

Question. A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the names of black and green coatings.
Answer: Silver gets tarnished when exposed to the atmosphere which contains pollutant H₂S and forms a black coating of Ag₂S. Copper forms a green deposit on its surface when exposed to moist air. This is usually basic copper (II) sulphate. The chemical phenomenon responsible is corrosion.
In simple words: Both coins are corroding - silver turns black due to sulfur pollution in air, while copper turns green due to moisture and air reactions.

📝 Teacher's Note: Connect to real-life observations - tarnished silver jewelry, green copper roofs on old buildings like the Statue of Liberty. Explain atmospheric pollution effects.

🎯 Exam Tip: Name the phenomenon (corrosion), identify the compounds (Ag₂S and basic copper sulphate), and mention the environmental causes (H₂S pollution, moist air).

Question 17. Aluminium is said to be more reactive than iron, towards oxygen (or air) yet iron undergoes corrosion to a greater extent than aluminum. Explain.
Answer: Aluminium forms white colour oxide on exposure to the atmosphere. This white colour oxide prevents it from further corrosion whereas iron reacts with air to form hydrated oxide called rust. So, iron undergoes corrosion to greater extent.

📝 Teacher's Note: Use a simple analogy - aluminum forms a protective "jacket" of oxide that prevents further damage, while iron's rust layer is porous and allows more corrosion. Show students pieces of aluminum foil and rusted iron to demonstrate this concept visually.

🎯 Exam Tip: Always mention that aluminum oxide forms a protective layer while iron rust is non-protective and porous - this contrast is key to scoring full marks.

Question 18. Which metals do not corrode easily?
Answer: The noble metals such as gold and platinum do not corrode easily.

📝 Teacher's Note: Explain that "noble" means unreactive - these metals are like "royalty" in the metal world, staying pure and unchanged. Students often confuse this with expensive metals, so clarify the chemical meaning.

🎯 Exam Tip: Remember the term "noble metals" specifically - writing just "unreactive metals" may not get full credit in some marking schemes.

Question 19. Why do gold ornaments look new even after several years of use?
Answer: Gold is the most unreactive metal so it does not react with air or water and other gases in atmosphere. So gold does not corrode. That is why gold look new after several years of use.

📝 Teacher's Note: Connect this to why gold has been valued throughout history - its permanent shine and resistance to tarnishing made it perfect for jewelry and currency. This helps students understand the practical applications of chemical properties.

🎯 Exam Tip: Emphasize gold's position at the bottom of the reactivity series and mention that it doesn't react with air, water, or atmospheric gases for complete marks.

Exercise 7(C)

Question 1. Define the term 'metallurgy'. State the processes involved in metallurgy.
Answer: The process used for the extraction of metals in their pure form from their ores is referred to as Metallurgy. The processes involved in Metallurgy are: 1. Crushing and Grinding 2. Concentration 3. Roasting and calcination 4. Reduction 5. Refining

📝 Teacher's Note: Use the analogy of cooking - you need to clean ingredients (concentration), prepare them (roasting/calcination), cook them (reduction), and garnish (refining). This sequence helps students remember the logical order of metallurgical processes.

🎯 Exam Tip: List all five processes in the correct order - partial lists often lose marks even if the definition is correct.

Question 2. Which metal occurs as: (a) a sulphide (b) a halide (c) a carbonate (d) an oxide Also give the names of their repective ores
Answer: (a) A metal which occurs as sulphide is lead. (b) A metal which occurs as halide is silver. (c) A metal which occurs as carbonate is zinc. (d) A metal which occurs as oxide is iron.

📝 Teacher's Note: Create memory aids - "Lead Sulks" (lead sulphide), "Silver Halts" (silver halide), "Zinc Carbonates" (zinc carbonate), "Iron Oxidizes" (iron oxide). Students should also know the actual ore names like galena, calamine, etc.

🎯 Exam Tip: The question asks for ore names too - include galena (PbS), horn silver (AgCl), calamine (ZnCO₃), and hematite (Fe₂O₃) for complete answers.

Question 3. Distinguish between: (a) a mineral and an ore, (b) an ore and a metallic compound
Answer: (a) Minerals are naturally occurring compounds of metals which are generally present with other matter such as soil, sand, limestone and rocks. Ores are those minerals from which the metals are extracted commercially at low cost and comfortably. All ores are minerals, but all minerals are not necessarily ores. (b) Ores are those minerals from which the metals are extracted commercially at low cost and with minimum effort. A metallic compound is a compound that contains one or more metal elements. Examples: AgNO₃ - Silver nitrate is a metallic compound.

📝 Teacher's Note: Use the analogy that all ores are minerals (like all roses are flowers) but not all minerals are ores (not all flowers are roses). The key difference is economic viability - can we extract metal profitably?

🎯 Exam Tip: Always mention "commercial extraction" and "economic viability" when defining ores - this economic aspect is crucial for full marks.

Question 4. Which metal can be extracted from each one of the following ores. (a) bauxite (b) calamine (c) haematite
Answer: The metals that can be extracted from the following ores are: (a) Bauxite- Aluminium (b) Calamine- Zinc (c) Haematite- Iron

📝 Teacher's Note: Teach students to recognize common ore names - bauxite (aluminum ore), calamine (zinc ore), hematite (iron ore). Create visual associations or use the first letters as memory aids.

🎯 Exam Tip: Learn the spelling of these ore names correctly - "haematite" not "hematite", "bauxite" not "boxite" - spelling errors can cost marks.

Question 5. State three objectives achieved during the roasting of ores
Answer: Three objectives achieved during the roasting of ores is: 1. It removes moisture from ores. 2. It makes the ore porous and more reactive. 3. It expels volatile impurities. 4. It converts sulphide ores into oxides.

📝 Teacher's Note: Even though the question asks for three objectives, the answer provides four - this shows complete understanding. Emphasize that roasting is like "preparing" the ore for the main extraction process.

🎯 Exam Tip: If asked for three points but you know four, write all four - examiners appreciate extra correct information and won't penalize you for knowing more.

Question 6. Give the principles of: (a) hydrolytic method, (b) froth floatation (c) electromagnetic separation
Answer: (a) Hydraulic washing: The difference in the densities of the ore and the gangue is the main criterion. (b) Forth floatation: This process depends on the preferential wettability of the ore with oil and the gangue particles by water. (c) Electromagnetic separation: Magnetic properties of the ores.

📝 Teacher's Note: Demonstrate these principles with simple classroom examples - heavy and light objects in water (hydraulic), oil and water separation (froth flotation), and magnets attracting iron filings (magnetic separation).

🎯 Exam Tip: Use the exact scientific terms - "preferential wettability" and "density difference" show precise understanding and score better than general descriptions.

Question 7. Name: (a) the processes involved in (i) concentration (ii) refining of ores (b) two metallic oxides which cannot be reduced by carbon, carbon monoxide or hydrogen
Answer: (a) The processes involved in (i) Processes involved in concentration are: 1. Hydrolytic method 2. Magnetic Separation 3. Froth floatation 4. Leaching (ii) Processes involved in Refining of ores are: 1. Distillation 2. Liquation 3. Oxidation 4. Electro-refining (b) Potassium and sodium oxides cannot be reduced by carbon, carbon monoxide and hydrogen.

📝 Teacher's Note: Connect this to the reactivity series - highly reactive metals like K and Na have such strong attraction to oxygen that common reducing agents can't break those bonds. This is why we need electrolysis for these metals.

🎯 Exam Tip: For part (b), any two highly reactive metal oxides work - K₂O, Na₂O, CaO, MgO, Al₂O₃ are all correct examples. Choose the ones you remember best.

Question 8. Explain the following terms: (a) flux (b) gangue (c) slag (d) smelting
Answer: (a) Flux: A flux is a substance that is added to the charge in a furnace to remove the gangue. (b) Gangue: Earthly impurities including silica, mud etc., associated with the ore are called gangue. (c) Slag: It is the fusible product formed when flux reacts with impurities during the extraction of metals. (d) Smelting: Smelting is the process of reducing the roasted oxide ore and removing the gangue with the help of an appropriate flux added with the ore.

📝 Teacher's Note: Use the analogy of cooking soup - gangue is like unwanted bits, flux is like a strainer that helps separate them, and slag is the removed waste. This makes these abstract terms more concrete for students.

🎯 Exam Tip: Remember the relationship: Flux + Gangue → Slag. This equation-like thinking helps ensure you mention all the key components in your definitions.

Question 9. Why does iron or zinc not occur free in nature?
Answer: Iron and zinc are quite reactive and hence they do not occur in the free state. The compounds of metals found in nature are their oxides, carbonate and sulphides.

📝 Teacher's Note: Relate this to the reactivity series and everyday observations - students can see iron rusting and zinc reacting with acids in school labs. This reactive nature means these metals immediately combine with other elements in nature.

🎯 Exam Tip: Always connect the answer to reactivity and mention that they exist as compounds (oxides, carbonates, sulphides) - this shows complete understanding of the concept.

Question 10. What do you observe when hydrogen is passed over heated copper oxide?
Answer: Black copper oxide is reduced to brown/red. \( \text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O} \)

📝 Teacher's Note: This is a classic demonstration - the color change from black to reddish-brown is very striking and helps students visualize reduction reactions. Always emphasize the observation (color change) before explaining the chemistry.

🎯 Exam Tip: Mention both the color change (observation) AND write the balanced chemical equation - questions asking "what do you observe" often expect both visual observation and chemical explanation.

Question 11. Compare roasting and calcination
Answer: Comparison of roasting and calcinations:

📝 Teacher's Note: The key difference is presence vs absence of air - roasting uses air to oxidize sulfur to SO₂, while calcination drives off CO₂ and water without air. Use heating different substances as classroom examples.

🎯 Exam Tip: Always mention the presence or absence of air as the first point - this is the fundamental difference that determines which process is used.

Question 12. (a) Name an ore of zinc. (b) which process is applied to concentrate it? (c) How is concentrated ore changes to oxide?
Answer: (a) Ore of zinc is zinc blende (ZnS). (b) It is concentrated by Froth floatation process. (c) Concentrated ore is changed into oxide by heating ZnS in excess of air. 2ZnS + 3O₂ \( \xrightarrow{800°C} \) 2ZnO + 2SO₂

📝 Teacher's Note: This question follows the logical sequence of metallurgy - identify ore, concentrate it, then convert to oxide. Help students see this as a step-by-step process rather than isolated facts.

🎯 Exam Tip: For part (c), always write the balanced chemical equation with temperature conditions - this shows complete understanding of the roasting process.

Question 13. Some metallic oxides can be reduced by hydrogen, carbon and carbon monoxide and some cannot. explain
Answer: Oxides of highly active metals like potassium, sodium, calcium, magnesium and aluminium have great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide or hydrogen. Metals in the middle of activity series (iron, zinc, lead, copper) are moderately reactive and are not found in oxide form. These are found in nature as sulphides or carbonate. These are first converted into oxides and can be reduced by C, CO or H₂. \( \text{ZnO} + \text{C} \xrightarrow{400°C} \text{Zn} + \text{CO} \) \( \text{PbO} + \text{CO} \rightarrow \text{Pb} + \text{CO}_2 \) Metals low in the activity series is very less reactive and oxides of these metals are reduced to metals by heating alone.

📝 Teacher's Note: Draw the reactivity series on the board and show how extraction methods change from top (electrolysis) to middle (reduction) to bottom (heating alone). This visual helps students understand the pattern.

🎯 Exam Tip: Organize your answer by reactivity levels - highly active, moderately active, and less active metals. This systematic approach ensures you cover all cases and score maximum marks.

Question 14. How are the following metallic oxides reduced. Write equations: (a) Iron (II) oxide, (b) Zinc oxide
Answer: (a) Iron(II) oxide: 4FeO + O₂ → 2Fe₂O₃ \( \text{Fe}_2\text{O}_3 + 3\text{CO} \xrightarrow{600°C-400°C} 2\text{Fe} + 3\text{CO}_2 \) (b) Zinc oxide is reduced by coke. \( \text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO} \)

📝 Teacher's Note: Point out that the first equation shows oxidation of FeO to Fe₂O₃, then reduction. This two-step process is important in blast furnace operations. Emphasize the role of carbon monoxide vs carbon as reducing agents.

🎯 Exam Tip: Include temperature conditions where given and ensure all equations are balanced - unbalanced equations often lose marks even if the concept is correct.

Question 15. State why aluminium is extracted from its oxide by electrolysis while copper, lead, iron by reducing agents and mercury and silver by thermal decomposition.
Answer: Aluminium has a great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide. So it is extracted from its oxide by electrolysis. Metals like copper, lead and iron are placed in the middle of the activity series and re moderately reactive and their oxides can be reduced by carbon, CO and hydrogen. Mercury and silver are less reactive and are placed lower in the reactivity series. The oxides of these metals are reduced to metals by heating their oxides.

📝 Teacher's Note: This question perfectly demonstrates how the reactivity series determines extraction methods. Create a simple chart showing High reactivity → Electrolysis, Medium → Reduction, Low → Heating alone.

🎯 Exam Tip: Always relate your answer to position in the reactivity series - this shows you understand the fundamental principle behind different extraction methods rather than just memorizing facts.

Question 16. An ore on being heated in air forms sulphurous anhydride. Write the process used for the concentration of this ore.
Answer: The process used for the concentration of the ore is froth floatation process.
In simple words: When an ore produces sulphur dioxide gas on heating, it means it contains sulphur compounds, and froth floatation is the best method to separate such ores from unwanted materials.

📝 Teacher's Note: Explain that sulphurous anhydride is SO₂, which forms when sulphide ores are heated. Connect this to why froth floatation works well for sulphide ores — they are hydrophobic and stick to air bubbles.

🎯 Exam Tip: Remember: sulphurous anhydride = SO₂ = sulphide ore = froth floatation. This logical chain helps avoid confusion with other concentration methods.

Question 17. (a) on which factors does purification of metals depend? (b) name the methods used for purification (c) How is electro-refining done?
Answer: (a) The purification depends upon: 1. Nature of metal. 2. Nature of impurities present in the metal. 3. Purpose for which metal is to be used (b) Methods used for purification are: 1. Distillation 2. Liquation 3. Oxidation 4. Electro-refining (c) The impure metal is made the anode, while a thin sheet of pure metal is made the cathode. Electrolyte used is a salt solution of a metal which is to be refined. Pure metal deposits at the cathode and impurities settle down forming anode mud.
In simple words: Different metals need different purification methods depending on what they are mixed with and what we plan to use them for. Electro-refining uses electricity to move pure metal from dirty metal to clean metal.

📝 Teacher's Note: Use the analogy of sorting mixed coins — different methods work for different types of "mixing." Demonstrate electro-refining with a simple copper sulphate solution and copper electrodes.

🎯 Exam Tip: For electro-refining, always mention: impure metal = anode, pure metal = cathode, and that impurities form "anode mud" at the bottom.

Question 18. Complete the following chemical equations: (a) \( Ag_2O \rightarrow \) (b) \( MnO_2 + 4Al \rightarrow \) (c) \( Cu(OH)_2 \rightarrow \) (d) \( ZnCO_3 \rightarrow \) (e) \( 2NaNO_3 \rightarrow \) (f) \( 2Pb(NO_3)_2 \rightarrow \) (g) \( 2AgNO_3 \rightarrow \) (h) \( 2Cu_2O + Cu_2S \rightarrow \) (i) \( HgS + O_2 \rightarrow \)
Answer: Balanced equations are: (a) \( 2Ag_2O \rightarrow 4Ag + O_2 \) (b) \( 3MnO_2 + 4Al \rightarrow 3Mn + 2Al_2O_3 + heat \) (c) \( Cu(OH)_2 \rightarrow CuO + H_2O \) (d) \( ZnCO_3 \rightarrow ZnO + CO_2 \) (e) \( 2NaNO_3 \rightarrow 2NaNO_2 + O_2 \) (f) \( 2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2 \) (g) \( 2AgNO_3 \rightarrow 2Ag + 2NO_2 + O_2 \) (h) \( 2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2 \) (i) \( HgS + O_2 \rightarrow Hg + SO_2 \)
In simple words: These are thermal decomposition reactions where heat breaks down compounds into simpler substances, often releasing gases like oxygen or carbon dioxide.

📝 Teacher's Note: Group these by reaction type — oxides decomposing to metals, hydroxides to oxides, carbonates releasing CO₂, nitrates releasing oxygen. This helps students see patterns.

🎯 Exam Tip: Always balance equations step by step. Count atoms of each element on both sides to ensure they match before writing your final answer.

Exercise 7(D)

Question 1. State the position of aluminium in the periodic table.
Answer: Position in the Periodic Table : Period 3, Group IIIA(13)
In simple words: Aluminium is in the third row and thirteenth column of the periodic table, making it a metal that easily gives away three electrons.

📝 Teacher's Note: Connect the group number (13) to the number of electrons in the outer shell (3). Use the periodic table to show how position determines properties.

🎯 Exam Tip: Remember Period 3, Group 13 (or IIIA in older notation). The group number tells you it has 3 valence electrons.

Question 2. Give the chemical names and formulae of any three ores of aluminium.
Answer: The chemical names and formulae of the ores of aluminium are:

In simple words: Bauxite is the main ore (with water attached), cryolite helps in extraction, and corundum is pure aluminium oxide found in nature.

📝 Teacher's Note: Emphasize that bauxite is the most important commercial ore. Show how "hydrated" means water molecules are attached to the compound.

🎯 Exam Tip: Learn all three with their formulas. Bauxite is the most commonly asked, but questions often require naming three ores.

Question 3. Which impurities are present in bauxite.
Answer: Bauxite ore contains approximately 60% aluminium oxide. The rest being sand, ferric oxide and titanium oxide.
In simple words: Bauxite is not pure — it's mixed with sand (silicon dioxide), iron oxide (rust-like substance), and titanium oxide, which need to be removed.

📝 Teacher's Note: Relate these impurities to everyday materials — sand (beaches), iron oxide (rust), titanium oxide (white paint). This makes abstract chemistry more concrete.

🎯 Exam Tip: Remember the three main impurities: sand (SiO₂), ferric oxide (Fe₂O₃), and titanium oxide (TiO₂). These must be removed during processing.

Question 4. What is red mud, how is it removed?
Answer: Red mud consists of ferric oxide, sand etc. left after bauxite dissolves in NaOH forming sodium aluminate and is removed by filtration.
In simple words: Red mud is the leftover waste (mainly iron oxide and sand) that doesn't dissolve when we treat bauxite with sodium hydroxide, and we simply filter it out.

📝 Teacher's Note: Use the analogy of making tea — the tea dissolves but the tea leaves remain and are filtered out. Show students actual red mud samples if available.

🎯 Exam Tip: Connect red mud to the Bayer process. Write: bauxite + NaOH → sodium aluminate (dissolves) + red mud (filtered out).

Question 5. Why electrolytic reduction is done to obtain aluminium?
Answer: As aluminium has great affinity for oxygen, so it is stable compound. It is not easily reduced by common reducing agents like carbon, carbon monoxide or hydrogen. Hence, electrolytic reduction is chosen as the method for reducing alumina.
In simple words: Aluminium loves oxygen so much that ordinary methods like heating with carbon won't separate them — we need the powerful force of electricity to pull them apart.

📝 Teacher's Note: Compare with less reactive metals like copper or lead that can be reduced with carbon. Use the reactivity series to show where aluminium stands.

🎯 Exam Tip: Key phrase: "high affinity for oxygen" means strong attraction. This is why we need electrolysis instead of simple chemical reduction.

Question 6. Give the ionization reactions of electrolyte used in Hall's process. write the reaction at the cathode and the anode. Why the anode has to be replaced in this process?
Answer: The ionization reactions of electrolyte in Hall's process: 1. Cryolite: \( Na_3AlF_6 \rightleftharpoons 3Na^+ + Al^{3+} + 6F^- \) 2. Fluorspar: \( CaF_2 \rightleftharpoons Ca^{2+} + 2F^- \) 3. Alumina: \( Al_2O_3 \rightleftharpoons 2Al^{3+} + 3O^{2-} \) The reaction at the cathode and anode are: Cathode: \( 4Al^{3+} + 12e^- \rightarrow 4Al \) Anode: \( 6O^{2-} - 12e^- \rightarrow 6[O] \) \( 3O + 3O \rightarrow 3O_2 \) The anode has to be replaced from time to time as it gets oxidized by the oxygen evolved at the anode.
In simple words: The electrolyte breaks into ions, aluminium forms at the negative electrode, oxygen forms at the positive electrode, and this oxygen burns up the carbon anode which needs regular replacement.

📝 Teacher's Note: Demonstrate with a simple electrolysis setup. Explain why carbon anodes are used (conduct electricity, relatively unreactive) and why they still get consumed (oxygen is very reactive).

🎯 Exam Tip: Remember the key reactions and always mention that oxygen attacks the carbon anode, requiring replacement. This is a common 2-mark question.

Question 7. (a) Name the process by which the refining of aluminium is done. (b) Where are the cathode and anode in the electrolytic cell? Name the material used for these? (c) state the reactions at the two electrodes.
Answer: (a) The process by which refining of aluminium is done is called Hoope's electrolytic process. (b) Molten impure aluminium forms the bottom layer. The bottom layer has carbon lining and serves as anode. Pure molten aluminium with carbon electrodes serves as cathode in top layer. (c) Reactions at the two electrodes are: Anode: \( Al - 3e^- \rightarrow Al^{3+} \) Cathode: \( Al^{3+} + 3e^- \rightarrow Al \)
In simple words: Hoope's process uses electricity to move aluminium from the impure bottom layer to the pure top layer, leaving impurities behind.

📝 Teacher's Note: Draw a diagram showing the three layers — pure aluminium (top), electrolyte (middle), impure aluminium (bottom). Emphasize the density differences that keep layers separate.

🎯 Exam Tip: Remember: impure Al = bottom = anode, pure Al = top = cathode. The process name "Hoope's" is often asked specifically.

Question 8. How does aluminum react with the following: (a) Air, (b) Water, (c) Acid, (d) Base
Answer: Reaction of aluminium: (a) Air: Aluminium forms oxide at room temperature. Aluminium powder burns in air at about 800°C forming its oxide and nitride with a bright light. \( 4Al + 3O_2 \rightarrow 2Al_2O_3 \) \( 2Al + N_2 \rightarrow 2AlN \) (b) Water: Water has no action on aluminium due to layer of oxide on it. When steam is passed over pure heated aluminium, hydrogen is produced. \( 2Al + 3H_2O \rightarrow Al_2O_3 + 3H_2 \) (c) Acid: It reacts with acids to produce salt and hydrogen. \( 2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2 \) Dilute sulphuric acid reacts with metal to liberate hydrogen. \( 2Al + 3H_2SO_4 \text{ (dilute)} \rightarrow Al_2(SO_4)_3 + 3H_2 \) Concentrated sulphuric acid reacts with aluminium to produce sulphur dioxide. \( 2Al + 6H_2SO_4 \rightarrow Al_2(SO_4)_3 + 6H_2O + 3SO_2 \) Dilute and concentrated nitric acid does not attack the metal aluminium. (d) Base: Aluminium reacts with boiling and dilute alkalies to produce meta aluminate while with fused alkali produce aluminate. \( 2Al + 2NaOH + 2H_2O \rightarrow 2NaAlO_2 + 3H_2 \) (Sodium meta aluminate) \( 2Al + 6NaOH \rightarrow 2Na_3AlO_3 + 3H_2 \) (Sodium aluminate)
In simple words: Aluminium reacts with air to form a protective layer, doesn't react with cold water, produces hydrogen gas with acids, and dissolves in strong bases producing hydrogen.

📝 Teacher's Note: Emphasize the protective oxide layer concept — it's why aluminium doesn't corrode like iron. Show the difference between concentrated and dilute acid reactions.

🎯 Exam Tip: Remember that aluminium is amphoteric (reacts with both acids and bases). The protective oxide layer explains its apparent inactivity with water.

Question 9. What is the role of cryolite (\( Na_3AlF_6 \)) in the electrolytic reduction of alumina in Hall's process?
Answer: The role of cryolite in the electrolytic reduction of alumina in Hall's process is: 1. Lowers the fusion temperature from 2050°C to 950°C and enhances conductivity. 2. Increases its conductivity since pure alumina is almost a non-conductor of electricity. 3. Cryolite acts as a solvent for the electrolytic mixture.
In simple words: Cryolite helps melt alumina at a lower temperature, makes it conduct electricity better, and acts like a solvent to dissolve everything properly.

📝 Teacher's Note: Use the analogy of salt on icy roads — just as salt lowers the melting point of ice, cryolite lowers the melting point of alumina. Explain the economic importance of lower temperatures.

🎯 Exam Tip: Remember three roles: lowers melting point, increases conductivity, acts as solvent. This saves energy and makes the process economically viable.

Question 10. (a) Aluminium is a more active metal than iron, but suffers less corrosion. Why? (b) Explain and give reasons why aluminium vessels should not be cleaned with powders containing alkalis.
Answer: (a) Aluminium is more active metal but it gets oxidized and forms a thin protective layer on its surface which prevents further corrosion. (b) Aluminium vessels should not be cleaned with powders containing alkalis because it results in the formation of meta aluminates and hydrogen. \( 2Al + 2NaOH + 2H_2O \rightarrow 2NaAlO_2 + 3H_2 \)
In simple words: Aluminium forms its own protective coating that stops rusting, but alkali cleaners can dissolve this coating and damage the metal vessel.

📝 Teacher's Note: Compare with iron rusting — iron oxide is porous and allows further corrosion, while aluminium oxide is protective. Demonstrate why alkaline cleaners damage aluminium cookware.

🎯 Exam Tip: Key concept: protective oxide layer. For part (b), mention that alkalis dissolve aluminium and produce hydrogen gas, which can damage the vessel.

Question 11. (a) Give the name and formula of the main ore of iron and zinc (b) How is the main ore of aluminium concentrated? (c) Why 'the food containing iron salts' should not be cooked in aluminium utensils?
Answer: (a) The main ores of iron and zinc are:

(b) Conversion of Impure Bauxite to Sodium aluminate \( Al_2O_3.2H_2O + 2NaOH \xrightarrow{150°C-200°C} 2NaAlO_2 + 3H_2O \) Impurities such as \( Fe_2O_3 \) and \( SiO_2 \) remain unaffected with conc.NaOH. Conversion of Sodium aluminate to Aluminium hydroxide. \( NaAlO_2 + 2H_2O \xrightarrow{50°C-60°C} NaOH + Al(OH)_3 \) Conversion of \( Al(OH)_3 \) to pure Alumina. \( 2Al(OH)_3 \xrightarrow{1100°C} Al_2O_3 + 3H_2O \) (c) A layer of aluminium is formed on iron at high temperature during cooking and food becomes deficient in iron.
In simple words: When cooking iron-rich foods in aluminium pots, the aluminium can react with iron compounds, reducing the iron content in the food and making it less nutritious.

📝 Teacher's Note: Explain the Bayer process step by step using simple language. For part (c), relate to nutrition — iron deficiency is a real health concern, especially in developing countries.

🎯 Exam Tip: For concentration, remember the three-step process: bauxite → sodium aluminate → aluminium hydroxide → pure alumina. Each step has a specific temperature and purpose.

Question 12. Explain with reasons: (a) In the electrolytic reduction of alumina, the graphite anode is gradually consumed. (b) Roasting is carried out on sulphide ores and not on carbonate ores. (c) Carbon can reduce lead oxide but not aluminium oxide
Answer: (a) During electrolysis, oxygen is evolved at the anode which reacts with carbon of the graphite anode to form carbon dioxide, thus gradually consuming the anode. (b) Roasting converts sulphide ores to oxides which can be easily reduced. Carbonate ores directly decompose to oxides on heating (calcination), so roasting is not needed. (c) Carbon can reduce only those metal oxides which are below carbon in the reactivity series. Lead is below carbon while aluminium is above carbon in the reactivity series.
In simple words: Oxygen attacks carbon anodes, sulphide ores need oxygen treatment while carbonates just need heat, and carbon can only take oxygen from less active metals than itself.

📝 Teacher's Note: Use the reactivity series as a reference tool. Show how position in the series determines which reducing agents work for which metals.

🎯 Exam Tip: For (a) mention oxygen evolution attacking carbon. For (b) distinguish roasting (sulphides) from calcination (carbonates). For (c) use reactivity series position.

Question 12.
(a) In the electrolytic reduction of alumina, the graphite (anode) is oxidized by oxygen to CO and further forms CO2, so it is consumed and has to be replaced from time to time.
2C + O2 → 2CO
2CO + O2 → 2CO2
(b) Roasting provides oxygen to convert metallic sulphides into metallic oxide and SO2 which takes place when heated in excess of air.
Carbonate is converted into oxide by loss of CO2 which takes place in the absence of air and when heated strongly.
(c) Aluminium has a great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide or hydrogen whereas lead oxide can be easily reduced to metal lead by carbon.
PbO + C → Pb + CO
Answer: This explanation shows why graphite electrodes need replacement in aluminum production, the difference between roasting and calcination processes, and why aluminum requires electrolytic reduction while lead can be reduced with carbon. Aluminum's high affinity for oxygen makes it very difficult to extract using simple chemical reduction methods.
In simple words: Aluminum is so strongly bonded to oxygen that we need powerful electricity to separate them, while lead can be separated easily using carbon.

📝 Teacher's Note: Use the activity series to show students why some metals need electrolysis while others can be reduced with carbon. Draw the Hall-Héroult process diagram to make electrolytic reduction visual.

🎯 Exam Tip: Remember the key difference - highly reactive metals like aluminum need electrolysis, moderately reactive metals like lead can be reduced with carbon.

Question 13.
(a) Why is flux used in the blast furnace?
(b) what does it form with silica present in the ore?
(c) How is it removed?
Answer:
(a) Flux combines with the gangue to form a fusible mass called slag.
(b) It forms slag[CaSiO3] with silica.
(c) It is removed from upper outlet, slag being lighter float on molten iron.
In simple words: Flux is like a cleaner that grabs all the unwanted rocky materials and makes them float on top of the pure metal so they can be easily removed.

📝 Teacher's Note: Use the analogy of oil floating on water to explain how slag separates from molten iron. Demonstrate with a simple density experiment using different liquids.

🎯 Exam Tip: Always mention that slag is lighter than molten iron and floats - this physical property separation is key to scoring marks.

Question 14.
Name an ore which is concentrated by:
(a) forth floatation process,
(b) magnetic separation
Answer:
(a) Froth flotation process: Zinc blende[ZnS]
(b) Magnetic Separation: Haematite[Fe2O3]
In simple words: Different ores need different cleaning methods - some stick to bubbles (froth flotation) while others get attracted to magnets.

📝 Teacher's Note: Show students actual samples of magnetic and non-magnetic minerals if available. Explain that the choice of concentration method depends on the physical properties of the ore.

🎯 Exam Tip: Learn the specific ore examples for each concentration method - examiners often ask for specific ore names, not just the process.

Question 15.
Distinguish between electrolytic methods of reduction and refining.
Answer:
Electrolytic Reduction
(i) It is removal of oxide or halide from a metal.
(ii) Oxides of highly active metals like Na,K,Ca,Mg,Al are reduced by electrolytic reduction of their fused salts.
(iii) Oxides of these metals have great affinity for oxygen than carbon and cannot be reduced by carbon or CO or hydrogen.
Electrolytic refining of metals is the separation of residual impurities like Si and phosphorus.
(i) Presence of other metals and non-metals like Si and phosphorus.
(ii) Unreduced oxides and sulphides of metals.
It depends upon:
(i) Nature of metal
(ii) Purpose for which metal is to be obtained.
(iii) Nature of impurities present.
Impure metal is made anode while a thin sheet of pure metal is made cathode and electrolyte used is a salt of solution of a metal to be refined.
In simple words: Reduction means getting the pure metal from its ore compound using electricity, while refining means cleaning the already extracted metal to remove leftover impurities.

📝 Teacher's Note: Use two separate diagrams - one for electrolytic reduction (like Hall-Héroult process) and one for electrolytic refining (like copper purification) to show the clear difference in purpose.

🎯 Exam Tip: Remember the key difference - reduction extracts metal from compounds, refining purifies already extracted metal. Mention specific examples to get full marks.

Question 16.
Give three ways in which the metal zinc differs from the non-metals carbon. At least one of the differences must be a chemical difference.
Answer:
The three ways in which metal zinc differs from the non-metal carbon is:
1. Zinc has a valency 2 and carbon has valency 4.
2. Zinc does not form hydride but carbon does (CH4).
3. Oxides of zinc are amphoteric (ZnO) whereas oxides of carbon are acidic (CO2) and neutral (CO).
In simple words: Zinc and carbon behave completely differently - they have different combining capacities, carbon easily joins with hydrogen while zinc doesn't, and their oxides react differently with acids and bases.

📝 Teacher's Note: Demonstrate the amphoteric nature of ZnO by showing it reacts with both acids and bases. Compare this with CO2 which only reacts with bases.

🎯 Exam Tip: Always include at least one chemical difference when comparing metals and non-metals. Mention specific chemical formulas to show you understand the chemistry.

Exercise 7(E)

Question 1.
State a reason why zinc is used in:
(a) galvanization, (b) dry cells (c) cosmetics?
Answer:
(a) To prevent from rusting.
(b) Due to strong electropositive nature, it easily forms Zn+2 ions.
(c) Antiseptic in face creams.
In simple words: Zinc protects iron from rusting, gives electrons easily in batteries, and kills germs in cosmetics.

📝 Teacher's Note: Show students galvanized iron sheets and explain how zinc sacrifices itself to save iron. Connect this to the electrochemical series to show why zinc protects iron.

🎯 Exam Tip: Remember zinc's electropositive nature is the key - it easily loses electrons, which explains both its use in batteries and galvanization.

Question 2.
State on what special properties the use of each of these metals depends:
(a) aluminium (b) zinc
Answer:
(a) Aluminium:
(i) Being a strong, light and corrosion resistant metal, it is used in alloys.
(ii) Aluminium is light, it has high tensile strength, is resistant to corrosion, good conductor of heat, unaffected by organic acids and has attractive appearance. So it is used for making cooking utensils, in building and construction work.
(iii) Aluminium has a strong affinity for oxygen so it is used as a deoxidizer in the manufacture of steel.
(b) Zinc:
1. Zinc has a strong electropositive character, so it is used for coating iron and steel sheets to prevent them from rusting and this process is known as galvanization.
2. Due to strong electropositive nature, it forms Zn+2 ions, so it is used to make dry cell containers which act as negative electrode.
3. Zinc act as a reducing agent for many organic reductions and these reductions are employed in manufacturing drugs, dyes.
In simple words: Aluminum is useful because it's light yet strong and doesn't rust, while zinc is useful because it easily gives up electrons to protect other metals or power batteries.

📝 Teacher's Note: Compare aluminum and zinc by showing physical samples. Emphasize how their different properties lead to different applications - aluminum's lightness vs zinc's electropositive nature.

🎯 Exam Tip: Link each property directly to its application - examiners look for clear cause-and-effect relationships between metal properties and their uses.

Question 3.
Explain the following:
(a) zinc is used to cover iron so as to prevent rusting of iron ehy?
(b) A neutral gas other than oxygen which is formed at the anode during electrolysis of fused alumina
(c) Nitric acid can be stored in aluminium containers.
Answer:
(a) Zinc is electropositive metal than iron, gets oxidized and saves iron. Also zinc forms protective layer of ZnO on iron. This layer is sticky and impervious in nature and protects the iron metal underneath from rusting.
(b) A neutral gas other than oxygen which is formed at anode during electrolysis of fused alumina is carbon monoxide.
(c) Nitric acid can be stored in aluminium containers as the dilute and conc. nitric acid does not react with aluminum. It renders aluminium passive due to the formation of an oxide film on its surface.
In simple words: Zinc protects iron by sacrificing itself and forming a protective coating, carbon monoxide gas comes from the carbon electrodes, and aluminum becomes passive with a protective oxide layer when exposed to nitric acid.

📝 Teacher's Note: Explain passivation using the example of aluminum foil not dissolving in nitric acid. Show how the oxide layer acts like an invisible protective coating.

🎯 Exam Tip: For galvanization, mention both the sacrificial protection AND the physical barrier. For passivation, always mention oxide film formation.

Question 4.
State the use of:
(a) cast iron (b) wrought Iron (c) Mild steel, (d) hard steel.
Answer:
(a) Cast iron: It is used in drain pipes, gutter covers, weights and railings.
(b) Wrought iron: It is used in chains, horse shoes and electromagnets.
(c) Mild steel: It is to manufacture nuts, bolts etc.
(d) Hard steel: It is used to make tools.
In simple words: Different types of iron and steel have different carbon content, making them suitable for different purposes - from soft decorative items to hard cutting tools.

📝 Teacher's Note: Show students examples of different iron/steel objects if possible. Explain how carbon content affects hardness - more carbon means harder but more brittle.

🎯 Exam Tip: Remember the pattern - higher carbon content gives harder steel for tools, lower carbon gives softer steel for structural work.

Question 5.
Which metal is used for:
(a) making pipes, buckets, water tanks,
(b) lithographic plates for printing
(c) making face creams
Answer:
(a) Galvanized iron sheets
(b) Zinc
(c) Zinc
In simple words: Galvanized iron (iron coated with zinc) is used for water containers because it won't rust, while pure zinc is used in printing and cosmetics for its special properties.

📝 Teacher's Note: Explain why galvanized iron is better than plain iron for water storage. Show students how zinc's antiseptic properties make it useful in cosmetics.

🎯 Exam Tip: Don't confuse galvanized iron with pure iron - galvanized means coated with zinc for protection.

Question 6.
Give reasons, why aluminum is used in:
(a) making alloys
(b) wrapping chocolates
(c) painting electric and telegraphic poles
(d) In aluminiothermy
(e) In making ships
Answer:
(a) Aluminium being strong, light and corrosion resistant metal is used for making alloy.
(b) Aluminium is light, malleable and does not rust so it is used for wrapping chocolates.
(c) To prevent them from rusting.
(d) It is used in aluminothermy as it is a good reducing agent.
(e) As aluminium forms a film of aluminium oxide, it protects the ships from corrosion. So it is used for making ships.
In simple words: Aluminum's combination of being light, strong, and rust-proof makes it perfect for many applications from food packaging to ship building.

📝 Teacher's Note: Demonstrate aluminum's malleability with foil. Explain how the natural oxide layer protects aluminum from further corrosion, unlike iron which keeps rusting.

🎯 Exam Tip: Always mention the specific property that makes aluminum suitable for each use - lightness, malleability, corrosion resistance, or reducing power.

Question 7.
Aluminum is used in thermite welding:
(a) what is thermit?
(b) what is ignition mixture?
(c) write reaction for process?
Answer:
(a) A mixture of 3 parts of ferric oxide (Fe2O3) and one part of aluminium powder (Al).
(b) A mixture of Potassium chlorate and magnesium powder is the ignition mixture.
(c) Fe2O3 +2Al → Al2O3 +2Fe +heat
In simple words: Thermite is a special mixture that creates extremely hot temperatures when ignited, hot enough to weld railway tracks together.

📝 Teacher's Note: Emphasize the safety aspects of thermite reaction. Explain why this process is used for welding railway tracks where other methods won't work.

🎯 Exam Tip: Remember the exact ratio - 3 parts Fe2O3 to 1 part Al. Write the balanced chemical equation correctly for full marks.

Question 8.
What is an alloy? How do the properties of an alloy differ from its constituents?
Answer:
Alloy is a homogeneous mixture of two or more metals or of one or more metals with certain non-metallic elements.
The properties of alloys are often greatly different from those of the components.
For example: Gold is too soft to be used without small percentage of copper.
A low percentage of molybdenum improves the toughness and wear resistance of steel.
Bell metal is more sonorous than copper or tin.
Alnico an alloy of aluminium, nickel and cobalt can lift 60 times its own mass.
These added elements improve hardness, wear resistance, toughness and other properties.
In simple words: Alloys are metal mixtures that are much better than pure metals - like how mixing ingredients makes a cake better than eating flour or eggs separately.

📝 Teacher's Note: Bring examples of pure metals vs alloys if possible. Explain how the arrangement of different sized atoms in alloys makes them stronger than pure metals.

🎯 Exam Tip: Always give specific examples of how alloy properties differ from pure metal properties. Mention both the improvement and the reason for improvement.

Question 9.
Name three alloys of steel. Give their compositions and uses.
Answer:

In simple words: Different steel alloys are made for different jobs - stainless steel resists rust, manganese steel is super tough, and tungsten steel stays sharp at high speeds.

📝 Teacher's Note: Show students examples of these steel types in everyday objects. Explain how the added elements give each alloy its special properties.

🎯 Exam Tip: Learn the exact compositions and connect them to uses - chromium and nickel make stainless steel rust-resistant, tungsten makes steel stay hard at high temperatures.

Question 10.
Both brass and bronze contain copper as major constituents Name other elements in these alloys.
Answer:
The other element in Brass is Zinc.
The other elements in Bronze are Tin and Zinc.
In simple words: Brass is copper mixed with zinc, while bronze is copper mixed with tin and zinc - both are much harder and more useful than pure copper.

📝 Teacher's Note: Show students brass and bronze objects to demonstrate how different the properties are despite copper being the main component in both.

🎯 Exam Tip: Don't confuse brass and bronze - brass has zinc, bronze has tin. Both are copper alloys but have very different properties and uses.

Question 11.
Name an alloy of:
(a) aluminium used in aircraft construction
(b) lead used in electrical wiring or electrical work in joining metals.
(c) copper in electrical appliances or household vessels
(d) zinc used in simple voltaic cells
Answer:
(a) Duralumin
(b) Solder
(c) Brass
(d) Zinc amalgam
In simple words: Each alloy is specially designed for its job - duralumin is light but strong for planes, solder melts easily for joining wires, brass conducts electricity well, and zinc amalgam works well in batteries.

📝 Teacher's Note: Explain why pure metals often aren't good enough for specialized applications. Show how alloying improves specific properties needed for each use.

🎯 Exam Tip: Remember the specific alloy names for each application. These are commonly asked in exams and you need the exact name, not just the description.

Question 12. What is an amalgam? State its use with an example.
Answer: A mixture or an alloy of mercury with a number of metals or an alloy such as sodium, zinc, gold and silver as well as with some non-metals is known as amalgam. Dental amalgam is a mixture of mercury and a silver tin alloy.
In simple words: Amalgam is like a special mixture where mercury metal gets mixed with other metals to create something useful, just like how dental fillings are made.

📝 Teacher's Note: Show students real examples like old dental fillings or explain how gold miners once used mercury to extract gold. This makes the concept tangible and memorable.

🎯 Exam Tip: Always mention mercury as the key component and give the dental amalgam example for full marks.

Question 13. (a) state two properties of brass that render it more useful for some purpose than its components (b) a metal which forms a liquid alloys at ordinary temperature
Answer: (a) Two properties of brass that make it more useful than its components are: (i) It is malleable and ductile. (ii) It resists corrosion. (iii) Can be easily cast. (b) A metal which forms a liquid alloy at ordinary temperature is sodium.
In simple words: Brass is better than pure copper or zinc because it can be shaped easily without breaking and doesn't rust quickly. Sodium makes liquid mixtures at room temperature.

📝 Teacher's Note: Bring brass objects like door handles or musical instruments to class. Let students feel the difference in hardness compared to pure copper wire.

🎯 Exam Tip: Write any two properties clearly - malleability, ductility, corrosion resistance, or easy casting. For part (b), sodium is the standard answer.

Question 14. What is magnalium? Name the main elements present in it? Write its one use.
Answer: Magnalium is an alloy of aluminium with composition 90-95% and magnesium with composition 10-5%. It is used for making aircrafts.
In simple words: Magnalium is a special metal mixture made mostly of aluminium with a little bit of magnesium, used to build airplanes because it's light but strong.

📝 Teacher's Note: Emphasize why aircraft need lightweight yet strong materials. Connect this to students' experience with aluminum foil versus airplane construction.

🎯 Exam Tip: Remember the composition percentages (90-95% Al, 5-10% Mg) and always mention aircraft as the use for full marks.

Question 15. Name the constituents of: (a) Duralumin (b) solder, (c) Bronze (d) Invar
Answer: The constituents of (a) Duralumin are aluminium (95%), copper (4%), magnesium (0.5%) and manganese (0.5%). (b) Solder are lead (50%) and tin (50%). (c) Bronze are copper (80%), tin (18%) and zinc (2%). (d) Invar are iron (63%), nickel (36%) and carbon (1%).
In simple words: These are all special metal mixtures where different metals are combined in specific amounts to get desired properties like strength, resistance to heat, or easy melting.

📝 Teacher's Note: Create a simple chart showing these alloys and their uses. Students often confuse bronze and brass - emphasize that bronze contains tin while brass contains zinc.

🎯 Exam Tip: Learn the percentages for each alloy. Duralumin is mostly aluminum, solder is half-half lead and tin, bronze is mostly copper with tin.

Miscellaneous Exercise

Question 1. For each substance listed below, explain its significance in the extraction of aluminium. (a) bauxite (b) Sodium hydroxide (c) Cryolite (d) Graphite
Answer: (a) Bauxite: Aluminium is extracted from its main ore bauxite \( Al_2O_3 \cdot 2H_2O \). It contains 60% \( Al_2O_3 \). (b) Sodium hydroxide: Sodium hydroxide dissolves bauxite to form sodium meta aluminate, removes insoluble impurities from \( Al_2O_3 \) by forming red mud. \( Al_2O_3 \cdot 2H_2O + 2NaOH \xrightarrow{150°C-200°C} 2NaAlO_2 + 3H_2O \)
\( NaAlO_2 + 2H_2O \xrightarrow{50°C-60°C} NaOH + Al(OH)_3 \)
\( 2Al(OH)_3 \xrightarrow{1100°C} Al_2O_3 + 3H_2O \) (c) Cryolite: Cryolite lowers the M.P. from 2050°C to 950°C and enhances conductivity. (d) Graphite: Acts as cathode as well as anode.
In simple words: Each substance has a special job in making aluminum - bauxite is the raw material, sodium hydroxide cleans it, cryolite makes the process easier, and graphite conducts electricity.

📝 Teacher's Note: Draw a flowchart showing each step. Emphasize that without cryolite, the process would need much higher temperatures, making it economically unfeasible.

🎯 Exam Tip: For each substance, write both what it is and what it does. Include the temperature reduction for cryolite (2050°C to 950°C) for full marks.

Question 2. From the metals: copper iron, magnesium, sodium and zinc, select a different metal in each case which: (a) does not react with dilute hydrochloric acid (b) can form 2+ and 3+ ions (c) has a hydroxide that reacts with both acids and alkalis (d) for not react with cold water but reacts with steam when heated.
Answer: (a) Copper (b) Iron (c) Zinc (d) Magnesium
In simple words: Each metal has different reactivity levels - copper is least reactive, iron can lose different numbers of electrons, zinc hydroxide is amphoteric (reacts with both acids and bases), and magnesium needs heat to react with water.

📝 Teacher's Note: Demonstrate the reactivity series using simple lab experiments. Show how copper doesn't react with dilute HCl while zinc does vigorously.

🎯 Exam Tip: Remember the reactivity series order. Copper is below hydrogen so doesn't react with acids. Iron forms both \( Fe^{2+} \) and \( Fe^{3+} \) ions.

Question 3. Arrange the metals in (2) in the decreasing order of reactivity.
Answer: Arrangement of metal in decreasing order of reactivity are: Sodium > Magnesium > Zinc > Iron > copper
In simple words: This is the order from most reactive to least reactive - sodium reacts explosively, while copper barely reacts at all.

📝 Teacher's Note: Use the activity series chart. Show videos of sodium reacting with water versus copper's lack of reaction with acids to reinforce the concept.

🎯 Exam Tip: Learn the complete reactivity series. Sodium is most reactive (Group 1), copper is least reactive (below hydrogen in series).

Question 4. In order to obtain 1 tonne of aluminium the following inputs are required. 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide, Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite (a) when bauxite is treated with sodium hydroxide solution, what happens to (i) the aluminium oxide (ii) the iron (III) oxide (b) (i) Name the process used for the purification of bauxite (ii) Write the equation for the action of heat on aluminium hydroxide (c) (i) write the formulae of cryolite (ii) Write down the word which correctly completes the following sentences. By dissolving aluminium oxide in cryolite a ………. (conducting/non conducting) solution is produced. (iii) why is so much graphic required for the electrolytic process? (iv) Write the equation for the reaction which takes place at cathode. (d) In construction work, why is the alloy of alluminium duralumin used rather than pure aluminium?
Answer: (a) (i) The aluminium oxide forms sodium aluminate. \( Al_2O_3 \cdot 2H_2O + 2NaOH \xrightarrow{150°C-200°C} 2NaAlO_2 + 3H_2O \) (ii) The iron(III) oxide does not dissolve in NaOH and is removed by filtration. (b) (i) The process used for the purification of bauxite is called Bayer's process. (ii) The equation for the action of heat on aluminium hydroxide is: \( 2Al(OH)_3 \xrightarrow{1000°C} Al_2O_3 + 3H_2O \) (c) (i) The formula of the cryolite is \( Na_3AlF_6 \). (ii) Conducting (iii) In electrolytic process, the graphite acts as anode. The anode has to be replaced from time to time as it gets oxidized by the oxygen evolved at the anode. (iv) The reaction that occurs at cathode is: \( 4Al^{3+} + 12e^- \rightarrow Al \) (d) In construction the alloy of aluminium -duralumin is used because it is hard and resistant to corrosion.
In simple words: This question covers the complete aluminum extraction process - from cleaning the ore to getting pure metal through electricity, with each step having a specific purpose.

📝 Teacher's Note: Break this complex question into smaller parts. Use a flowchart to show how bauxite becomes pure aluminum through multiple steps.

🎯 Exam Tip: Remember Bayer's process for purification, \( Na_3AlF_6 \) for cryolite formula, and that graphite electrodes need replacement because they get consumed.

Question 5. Aluminium is extracted from its chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction (a) Write three balanced equation for the purification of bauxite (b) Name a chemical used for dissolving aluminium oxide, In which state of subdivision is the chemical used? (c) Write an equation for the reaction which takes place at the anode during the extraction of aluminium by the electrolytic process. (d) Mention one reason for the use of aluminium in thermite welding.
Answer: (a) Three balanced equations for purification of bauxite are: \( Al_2O_3 \cdot 2H_2O + 2NaOH \xrightarrow{150°C-200°C} 2NaAlO_2 + 3H_2O \)
\( NaAlO_2 + 2H_2O \xrightarrow{50°C-60°C} NaOH + Al(OH)_3 \)
\( 2Al(OH)_3 \xrightarrow{1100°C} Al_2O_3 + 3H_2O \) (b) Fluorspar and cryolite are used for dissolving \( Al_2O_3 \). This chemical is used in the middle state. (c) Reaction at anode: \( 6O^{2-} - 12e^- \rightarrow 6[O] \)
\( 3O + 3O \rightarrow 3O_2 \) Anode is oxidized to carbon monoxide and then to carbon dioxide. \( 2C + O_2 \rightarrow 2CO \)
\( 2CO + O_2 \rightarrow 2CO_2 \) (d) In Aluminium thermite welding, the reduction with aluminium is highly exothermic and heat generated is sufficient to melt the metal. \( Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3 + Heat \)
In simple words: The three equations show how bauxite is cleaned step by step, cryolite helps dissolve aluminum oxide, oxygen gas forms at the anode, and aluminum creates tremendous heat when it reacts.

📝 Teacher's Note: Emphasize that the three equations represent a complete cycle - dissolution, precipitation, and dehydration. Show the thermite reaction video if possible.

🎯 Exam Tip: Learn all three equations in sequence. For thermite welding, mention that aluminum reduces iron oxide and produces enormous heat.

Question 1(2005). (a) A to F below relate to the source and extraction of either zinc or aluminium: A. Bauxite B. Coke C. Cryolite D. Froth floatation E. Sodium hydroxide solution, F. Zinc blende (i) Write down the three letters each from the above list which are relevant to: 1. Zinc 2. Aluminum (ii) Fill in the blanks using the most appropriate words from A to F. 1. The ore from which aluminum is extracted must first be treated with …………. So that pure aluminum oxide can be obtained.
Answer: (i) 1. Zinc: Froth Flotation, Zinc Blende, Coke 2. Aluminium: Bauxite, Cryolite, Sodium hydroxide solution (ii) 1. Sodium hydroxide. 2. Cryolite (iii) The formula of Cryolite is \( Na_3AlF_6 \).
In simple words: Different materials are used for extracting different metals - zinc uses froth flotation and coke, while aluminum uses different chemicals and processes.

📝 Teacher's Note: Create two separate columns for zinc and aluminum extraction materials. This helps students categorize the processes clearly.

🎯 Exam Tip: Remember that zinc blende is zinc ore, bauxite is aluminum ore. Froth flotation is for zinc, sodium hydroxide is for aluminum purification.

Question 2(2005). Calcium copper, lead aluminium zinc chromium, magnesium and iron. Choose the major metals from the list given above to make the following alloys: (a) Stainless steel (b) brass
Answer: (a) Stainless steel: Iron, Chromium (b) Brass: Copper, Zinc
In simple words: Stainless steel is made by adding chromium to iron to prevent rusting, while brass is made by mixing copper and zinc.

📝 Teacher's Note: Show actual samples of stainless steel (spoons, knives) and brass (door handles, musical instruments) to help students connect theory with real objects.

🎯 Exam Tip: Remember: stainless steel = iron + chromium, brass = copper + zinc. These are the most common alloy compositions asked in exams.

Question (2006). Name the following: (a) A metal which is liquid at room temperature (b) The process of heating an ore to a high temperature in the presence of air. (c) The compound formed by the reaction between calcium oxide and silica (d) A compound which is added to lower the fusion temperature of the electrolytic bath in the extraction of aluminium. (e) Name an allotrope of a non-metal that allows electricity to pass through it.
Answer: (a) Mercury (b) Roasting (c) \( CaSiO_3 \) (d) Cryolite (e) Graphite
In simple words: Mercury is the only liquid metal at room temperature, roasting heats ore with air, calcium silicate forms from lime and sand, cryolite makes aluminum extraction easier, and graphite conducts electricity unlike other forms of carbon.

📝 Teacher's Note: Show students a thermometer with mercury (if available) and graphite from pencils. Explain how roasting differs from calcination (with vs without air).

🎯 Exam Tip: These are standard one-word answers. Mercury is the only liquid metal, graphite is the conducting form of carbon, cryolite always lowers melting point in aluminum extraction.

Question 1(2007). From the list of characteristics given below, select the five which are relevant to non-metals and their compounds: A. ductile B. Conduct electicity C. Brittle D. Acidic oxide E. Basic oxides F. Discharge at anode G. Discharge at cathode H. Ionic chlorides I. Covalent chlorides J. Reaction with dilute sulphuric acid yields hydrogen, K. 1, 2, or 3 valence electrons L. 5, 6, 7 valence electrons (write the five letters corresponding to the correct characteristics)
Answer: The five characteristics relevant to non-metals are: C (Brittle), D (Acidic oxide), G (Discharge at cathode), I (Covalent chlorides), L (5, 6, 7 valence electrons)
In simple words: Non-metals break easily, form acidic compounds, move toward negative electrode, make molecular compounds with chlorine, and have many outer electrons.

📝 Teacher's Note: Create a comparison chart of metal vs non-metal properties. Use examples like sulfur (brittle) vs copper wire (ductile) to illustrate differences.

🎯 Exam Tip: Remember non-metals are opposite to metals in most properties - brittle vs ductile, acidic vs basic oxides, covalent vs ionic compounds.

Solution 1 (2007):

Acidic oxide(D)
Discharged at anode (F)
Covalent chlorides (I)
5,6,7 valence electrons (L)
Brittle(C)

Question 2 (2007). The following is an extract from 'Metals in the service of Man, Alexander and street/pelican 1976:
'Alumina (aluminium oxide) has a very high melting point of over 2000° C so that it cannot readily be liquefies. However conversion of alumina to aluminium and oxygen, by electrolysis can occur when it is dissolved in some other substance'.
(i) Which solution is used to react with bauxide as a first step in obtaining pure aluminium oxide?
(ii) The aluminium oxide for the electrolytic extraction of aluminum is obtained by heating aluminium hydroxide. Write the equation for this reaction
(iii) Name the element which serves both as the anode and the cathode in the extraction of aluminum.
(iv) Write the equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.
(v) Give the equation for the reaction which at the anode when aluminum is purifies by electrolysis.
Answer:
(i) Sodium hydroxide
(ii) \( 2Al(OH)_3 \xrightarrow{heat, 1000°C} Al_2O_3 + 3H_2O \)
(iii) Graphite
(iv) Reaction at cathode: \( Al^{3+} + 3e^- \rightarrow Al \)
(v) Reaction at anode: \( Al - 3e^- \rightarrow Al^{3+} \)
In simple words: To extract aluminum, we first treat bauxite with sodium hydroxide to get pure aluminum oxide. Then we heat aluminum hydroxide to make aluminum oxide, use graphite electrodes, and apply electricity to separate aluminum metal at the cathode while aluminum gets oxidized back at the anode during purification.

📝 Teacher's Note: Use visual aids to show the Hall-Héroult process setup. Students often confuse the purification reactions with the extraction reactions, so emphasize the difference between these two processes clearly.

🎯 Exam Tip: Always write balanced chemical equations with proper state symbols and reaction conditions. Remember that graphite serves as both electrodes, and clearly distinguish between cathode reduction and anode oxidation reactions.

Question 1 (2008). The following is a sketch of an electrolytic cell used in the extraction of aluminium:
(i) What is the substance of which the electrodes A and B are made?
(ii) At which electrode (A or B) is the aluminum formed?
(iii) What are the two aluminum compounds in the electrolyte C?
(v) why is it necessary for electrode B to be continuously replaced?
Answer:
(i) A is made of carbon and B is thick graphite rod.
A → Cathode
B → Anode
(ii) Aluminium is formed at electrode A.
(iii) The two aluminium compound in the electrolyte C is \( Na_3AlF_6 \), \( Al_2O_3 \).
(iv) It is necessary to continuously replace electrode B from time to time as it gets oxidized by the oxygen evolved.
In simple words: In aluminum extraction, carbon electrodes are used where aluminum forms at the cathode (negative electrode). The electrolyte contains aluminum oxide dissolved in cryolite, and the anode needs replacement because oxygen gas produced there burns away the carbon electrode.

📝 Teacher's Note: Show students actual images of industrial aluminum extraction cells. Emphasize why cryolite is added - it lowers the melting point and increases conductivity of the electrolyte mixture.

🎯 Exam Tip: Remember the chemical formulas: \( Na_3AlF_6 \) for cryolite and \( Al_2O_3 \) for aluminum oxide. Always mention that the anode burns away due to oxygen evolution - this is a key point examiners look for.

Question 2 (2008). Brass is an alloy of:
(a) Copper and tin
(b) Copper and Zinc
(c) Zinc and lead
(d) Lead and tin
Answer: (b) Copper and Zinc
In simple words: Brass is made by mixing copper and zinc metals together, which creates a golden-colored alloy that's stronger than pure copper and commonly used in musical instruments and decorative items.

📝 Teacher's Note: Bring samples of different alloys to class if possible. Students often confuse brass (Cu + Zn) with bronze (Cu + Sn). Create a simple memory trick: "Brass has Zinc, Bronze has tiN".

🎯 Exam Tip: Remember common alloys: Brass = Copper + Zinc, Bronze = Copper + Tin, Steel = Iron + Carbon. These are frequently asked in objective questions.