RBSE Solutions Class 10 Science Chapter 5 Chemistry in Everyday Life

Multiple Choice Questions

Question 1. Aqueous solution of a base
(a) Turns blue litmus into red
(b) Turns red litmus into blue
(c) Turns litmus solution colourless
(d) Has no effect on litmus solution
Answer: (b) Turns red litmus into blue
In simple words: Bases are known to change the color of red litmus paper to blue. This is a classic test to identify a basic substance.

🎯 Exam Tip: Remember the phrase "B for Blue, B for Base" to easily recall how litmus paper reacts with bases.

Question 2. What is the conductive property of aqueous solution of acid or base?
(a) Bad conductor
(b) Good conductor
(c) Semiconductor
(d) No effect
Answer: (b) Good conductor
In simple words: When acids or bases dissolve in water, they create ions. These ions are charged particles that can move freely, allowing electricity to pass through the solution.

🎯 Exam Tip: The presence of free-moving ions is key for electrical conductivity in solutions. Strong acids and bases create more ions, making them better conductors.

Question 3. pH shows negative logarithm of concentration of which ions?
(a) [H2O]
(b) [OH-]
(c) [H+]
(d) [Na+]
Answer: (c) [H+]
In simple words: pH measures how acidic or basic a solution is, and it's directly related to the concentration of hydrogen ions (H+) in that solution. The more H+ ions, the lower the pH, making it more acidic.

🎯 Exam Tip: The pH scale is logarithmic, meaning a small change in pH value represents a large change in H+ ion concentration. Remember that pH = -log[H+].

Question 5. The digestion in stomach takes place in which type of medium?
(a) Acidic
(b) Alkaline
(c) Neutral
(d) Changing
Answer: (a) Acidic
In simple words: Our stomach produces hydrochloric acid, which creates a highly acidic environment needed for digestive enzymes to break down food effectively. This acidity also helps kill harmful bacteria.

🎯 Exam Tip: The stomach's acidic environment is crucial for the optimal functioning of enzymes like pepsin, which digests proteins.

Question 6. Which of the following substances is used in making fire extinguisher?
(a) Sodium carbonate
(b) Sodium hydrogen carbonate
(c) Plaster of Paris
(d) Sodium chloride
Answer: (b) Sodium hydrogen carbonate
In simple words: Sodium hydrogen carbonate, also known as baking soda, is commonly used in fire extinguishers because it releases carbon dioxide gas, which helps to smother flames. This gas cuts off the oxygen supply to the fire.

🎯 Exam Tip: Fire extinguishers often use chemical reactions to produce carbon dioxide (CO2), which is denser than air and acts as a barrier, preventing oxygen from reaching the fire.

Question 7. Which of the following is the formula of washing soda?
(a) NaHCO3
(b) NaCl
(c) CaSO4.1/2H2O
(d) Na2CO3.10H2O
Answer: (d) Na2CO3.10H2O
In simple words: Washing soda is sodium carbonate decahydrate, meaning it's sodium carbonate combined with ten water molecules. This compound is known for its cleaning properties.

🎯 Exam Tip: Pay close attention to the number of water molecules of crystallization in chemical formulas, as it distinguishes between different hydrated compounds like washing soda and anhydrous sodium carbonate.

Question 8. Which gas is released when bleaching powder is kept in open air?
(a) Chlorine
(b) Oxygen
(c) Carbon dioxide
(d) Hydrogen
Answer: (a) Chlorine
In simple words: When bleaching powder is exposed to the air, it reacts with carbon dioxide and moisture in the atmosphere to slowly release chlorine gas. This is why it has a characteristic smell.

🎯 Exam Tip: Bleaching powder's effectiveness and its characteristic smell come from the chlorine gas it releases. Proper storage in airtight containers helps maintain its potency by preventing premature release of chlorine.

Question 9. Soap works in which of the following?
(a) Soft water
(b) Hard water
(c) Both soft and hard water
(d) None of the options
Answer: (a) Soft water
In simple words: Soaps work well in soft water because they can easily form lather and clean. In hard water, soaps react with minerals to form scum, which reduces their cleaning power.

🎯 Exam Tip: Understand the difference between soap and detergent. Detergents are designed to work effectively in both soft and hard water without forming scum.

Question 10. Hydrocarbon tail is towards which side in a micelle?
(a) Towards centre
(b) On surface
(c) Keeps changing
(d) In any direction
Answer: (a) Towards centre
In simple words: In a micelle, the long, oil-loving hydrocarbon tails of soap molecules point inwards, trapping dirt and grease in the center. The water-loving heads point outwards.

🎯 Exam Tip: Remember that soap molecules are amphiphilic, meaning they have both a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail, which is essential for micelle formation.

Question 11. Compounds which accept proton are
(a) Acid
(b) Salt
(c) None of the options
(d) Base
Answer: (d) Base
In simple words: According to the Brønsted-Lowry definition, a base is a substance that can accept a hydrogen ion (proton) from another substance. Proton acceptance makes a substance basic.

🎯 Exam Tip: The Brønsted-Lowry theory expands on the Arrhenius definition, classifying acids as proton donors and bases as proton acceptors, which is helpful for reactions that don't occur in water.

Chemistry in Everyday Life Very Short Answer Type Questions

Question 12. What is released when a red ant stings?
Answer: When a red ant stings, it injects an acidic substance into the skin. This acid is called formic acid, and it causes the pain and irritation we feel. Applying a mild base can help neutralize this acid.
In simple words: A red ant sting injects acid, which causes pain.

🎯 Exam Tip: Many insect stings and bites involve acidic or basic secretions. Knowing this can help you choose the right home remedy, like baking soda for an acidic sting.

Question 14. What is neutralization?
Answer: Neutralization is a chemical reaction that occurs when an acid and a base react together. This reaction typically produces a salt and water, and often releases heat. It essentially balances the acidic and basic properties.
In simple words: Neutralization is when an acid and a base mix to make salt and water.

🎯 Exam Tip: In a perfect neutralization reaction, the pH of the resulting solution becomes 7, indicating a neutral state. Remember that it's the reaction between H+ and OH- ions that forms water.

Question 15. Which process is used for killing germs in drinking water?
Answer: Chlorination is the process used for killing germs in drinking water. This involves adding chlorine or chlorine compounds to the water, which effectively disinfects it by destroying harmful microorganisms. It is a common method for water purification.
In simple words: Chlorination is used to kill germs in drinking water.

🎯 Exam Tip: Chlorine is a powerful disinfectant because it can break down the cell walls of bacteria and viruses, making it highly effective for public health, but it must be used in controlled amounts.

Question 16. How does a metal oxide react with acid? Write the chemical equation for this.
Answer: Metal oxides are generally basic in nature. Therefore, when a metal oxide reacts with an acid, it undergoes a neutralization reaction, producing salt and water. This is similar to how a base reacts with an acid.
Metal oxide + Acid \( \rightarrow \) Salt + Water
e.g., \( \text{CuO} + 2\text{HCl} \rightarrow \text{CuCl}_2 + \text{H}_2\text{O} \)
In simple words: Metal oxides are like bases, so they react with acids to make salt and water.

🎯 Exam Tip: Always balance chemical equations to ensure that the number of atoms of each element is the same on both sides of the reaction. This demonstrates the conservation of mass.

Question 17. What is the meaning 'p' and 'H' in pH?
Answer: In the term "pH", 'p' stands for "Potenz" which means "power" or "potential" in German. 'H' stands for hydrogen, representing the concentration of hydrogen ions. So, pH indicates the power of hydrogen, which determines the acidity or alkalinity of a solution.
In simple words: In pH, 'p' means power, and 'H' means hydrogen, showing the power of hydrogen ions.

🎯 Exam Tip: Remember that pH is a measure of the *activity* of hydrogen ions. A lower pH means a higher concentration of hydrogen ions and stronger acidity.

Question 18. What will you take to get relief from hyperacidity?
Answer: To get relief from hyperacidity, which is an excess of acid in the stomach, you would take an antacid. Milk of magnesia, which is magnesium hydroxide, is a common example of an antacid. It works by neutralizing the excess stomach acid.
In simple words: Take milk of magnesia, an antacid, to feel better from too much stomach acid.

🎯 Exam Tip: Antacids are mild bases that react with hydrochloric acid in the stomach to reduce its acidity. Always ensure you are taking the correct type of medication for your symptoms.

Question 19. Write the names of any two salts of sodium.
Answer: Two common salts of sodium are sodium chloride (table salt) and sodium carbonate (washing soda). Sodium chloride is essential for life, while sodium carbonate is used in various industries.
In simple words: Two salts of sodium are sodium chloride and sodium carbonate.

🎯 Exam Tip: Many important chemical compounds in everyday life contain sodium. Knowing the chemical names and common names for these salts is a good way to understand basic chemistry.

Question 21. What is saponification?
Answer: Saponification is the chemical reaction that produces soap. It occurs when fatty acids or oils are heated with a strong alkaline solution, such as aqueous sodium hydroxide or potassium hydroxide. This process breaks down the fat or oil into glycerol and a soap molecule.
In simple words: Saponification is the process of making soap by mixing fat or oil with a strong base like sodium hydroxide.

🎯 Exam Tip: Saponification is a hydrolysis reaction where an ester (fat/oil) reacts with a base. The type of alkali used (sodium or potassium hydroxide) determines whether a hard or soft soap is produced.

Question 22. What is the speciality of detergent?
Answer: The speciality of detergents is their ability to perform cleansing action effectively even in hard water. Unlike soaps, detergents do not form insoluble scum with the calcium and magnesium ions present in hard water, allowing them to lather and clean well. This makes them more versatile for laundry.
In simple words: Detergents are special because they can clean well even in hard water, unlike soaps that make scum.

🎯 Exam Tip: Detergents achieve their hard water performance because their calcium and magnesium salts are soluble in water, preventing the formation of scum that occurs with soaps.

Question 23. Which compound is used for casting plaster on a broken bone?
Answer: Plaster of Paris is the compound used for casting plaster on a broken bone. It is chemically known as calcium sulfate hemihydrate. When mixed with water, it quickly sets into a hard, rigid mass, providing support and immobilization for the fractured bone.
In simple words: Plaster of Paris is used to make casts for broken bones because it hardens fast when mixed with water.

🎯 Exam Tip: The quick-setting property of Plaster of Paris is due to its rehydration and recrystallization into gypsum, forming a strong, interlocking crystal structure.

Question 24. The concentration of hydrogen ion in a solution is \( 1 \times 10^{-4} \) gm mole L\(^{-1}\). Find the pH of this solution. Is it an acidic or a basic solution?
Answer: The pH of a solution is calculated using the formula \( \text{pH} = -\text{log}[\text{H}^+] \). Given the hydrogen ion concentration, we can find the pH.
\( \text{pH} = -\text{log} [1 \times 10^{-4}] \)
\( \text{pH} = -(\text{log } 1 + \text{log } 10^{-4}) \)
\( \text{pH} = -(0 + (-4)) \)
\( \text{pH} = 4 \)
Since the pH value is 4, which is less than 7, the solution is acidic. Solutions with pH less than 7 are considered acidic.
In simple words: The pH of this solution is 4. Because 4 is less than 7, the solution is acidic.

🎯 Exam Tip: Remember that a pH of 7 is neutral, a pH less than 7 is acidic, and a pH greater than 7 is basic. The lower the pH, the stronger the acid.

Chemistry in Everyday Life Short Answer Type Questions

Question 25. Write the name and uses of two strong acids and two strong bases.
Answer: Two strong acids are Hydrochloric Acid (HCl) and Sulphuric Acid (H2SO4). Hydrochloric acid is used as a bathroom cleaner and in the steel industry to remove rust. Sulphuric acid is used as an electrolyte in car batteries and to make fertilizers and detergents.
Two strong bases are Sodium Hydroxide (NaOH) and Potassium Hydroxide (KOH). Sodium hydroxide is used in making soap and paper. Potassium hydroxide is used in alkaline batteries and some liquid soaps. These strong compounds are vital in many industrial processes.
In simple words: Hydrochloric acid and sulphuric acid are strong acids. Sodium hydroxide and potassium hydroxide are strong bases. They are used in cleaning, making batteries, and other industries.

🎯 Exam Tip: When listing uses, try to provide a diverse range of applications for each compound to show a broad understanding of its importance.

Question 27. Define acids and bases as per Arrhenius concept.
Answer: According to the Arrhenius concept:
\( \implies \) **Acid:** An acid is a substance that produces hydrogen ions (H\(^+\)) when dissolved in water. For example, HCl (hydrochloric acid) in water releases H\(^+\) ions. These H\(^+\) ions combine with water to form hydronium ions (H\( _3\)O\(^+\)).
\( \implies \) **Base:** A base is a substance that produces hydroxide ions (OH\(^-\)) when dissolved in water. For example, NaOH (sodium hydroxide) in water releases OH\(^-\) ions. The presence of OH\(^-\) ions makes the solution basic.
In simple words: Arrhenius said acids make H\(^+\) ions in water, and bases make OH\(^-\) ions in water.

🎯 Exam Tip: Remember that the Arrhenius definition specifically refers to substances dissolving in water. Other acid-base theories expand these definitions to include reactions in non-aqueous solutions.

Question 28. What is pH? Explain pH range of acidic and basic solutions.
Answer: pH is a measure of the acidity or alkalinity of a solution. It is defined as the negative logarithm of the hydrogen ion concentration \( [\text{H}^+] \) in a solution.
\( \text{pH} = -\text{log}[\text{H}^+] \)
For example, if the hydrogen ion concentration is \( 1 \times 10^{-4} \) gm mole L\(^{-1}\), then:
\( \text{pH} = -\text{log} [1 \times 10^{-4}] \)
\( \text{pH} = -(\text{log } 1 + \text{log } 10^{-4}) \)
\( \text{pH} = -(0 - 4) \)
\( \text{pH} = 4 \)

The pH scale ranges from 0 to 14.
\( \implies \) **Neutral Solution:** A neutral solution has a pH of 7. Pure water is an example of a neutral solution.
\( \implies \) **Acidic Solution:** An acidic solution has a pH less than 7. The lower the pH value (closer to 0), the stronger the acid. For instance, a pH of 4 indicates an acidic solution.
\( \implies \) **Basic Solution:** A basic (or alkaline) solution has a pH greater than 7. The higher the pH value (closer to 14), the stronger the base. For example, a pH of 9 indicates a basic solution.
In simple words: pH tells us how acidic or basic something is. A pH of 7 is neutral. If pH is below 7, it's acidic. If pH is above 7, it's basic.

🎯 Exam Tip: Always remember the pH scale's range and its key reference point (pH 7 for neutral). Understand that each unit change in pH represents a tenfold change in hydrogen ion concentration.

Question 30. What happens when:
(i) Curd or a sour substance is kept in metallic container.
(ii) Teeth are not cleaned after dinner.
Answer:
(i) Curd or sour substances contain acids, such as lactic acid in curd. If these are kept in metallic containers (like copper or brass), the acid reacts with the metal. This reaction produces hydrogen gas and forms toxic metallic salts, which can spoil the food and also damage the container. Eating such spoiled food can be harmful to health.
(ii) After dinner, food particles often remain stuck between teeth. Bacteria in the mouth feed on these food particles and produce acids. These acids then react with and dissolve the tooth enamel, which is primarily made of calcium phosphate. This process, called tooth decay, can lead to cavities and other dental problems if teeth are not cleaned regularly.
In simple words: (i) If you put sour food in metal containers, the acid in the food will react with the metal, spoiling the food and harming the container. (ii) If you don't clean your teeth after eating, bacteria make acid from leftover food, which then damages your tooth enamel, causing decay.

🎯 Exam Tip: Always relate chemical reactions to practical everyday situations, like food storage or oral hygiene, to illustrate your understanding of concepts like acid-metal reactions and acid-base balance.

Question 31. A substance A reacts with sulphuric acid and produces a gas B with effervescence. Gas B burns with a pop sound. Name A and B and write the equation for this reaction.
Answer: The substance A is Zinc metal. When Zinc reacts with sulphuric acid, it produces hydrogen gas (Gas B), which burns with a characteristic pop sound when a burning splinter is brought near it. This is a common test for hydrogen gas.
\( \text{Zn (s)} + \text{H}_2\text{SO}_4 \text{ (aq)} \rightarrow \text{ZnSO}_4 \text{ (aq)} + \text{H}_2 \text{ (g)} \)
Here, (s) denotes solid, (aq) denotes aqueous solution, and (g) denotes gas. Zinc replaces hydrogen from the acid.
In simple words: Substance A is Zinc metal, and Gas B is hydrogen. When zinc reacts with sulfuric acid, it makes zinc sulfate and hydrogen gas, which makes a pop sound when it burns.

🎯 Exam Tip: Remember the "pop sound" test is a definitive way to identify hydrogen gas in experiments. Metals typically react with acids to produce hydrogen gas and a salt.

Chemistry in Everyday Life Long Answer Type Questions

Question 32. Explain acid and base on the basis of Bronsted Lowry and Lewis concepts.
Answer:
**Brønsted-Lowry Concept of Acid and Base:**
\( \implies \) **Acid:** A Brønsted-Lowry acid is defined as a proton (H\(^+\)) donor.
\( \implies \) **Base:** A Brønsted-Lowry base is defined as a proton (H\(^+\)) acceptor.
For example, in the reaction \( \text{HCl}_{(\text{aq})} + \text{H}_2\text{O} \rightarrow \text{Cl}^{-}_{(\text{aq})} + \text{H}_3\text{O}^{+}_{(\text{aq})} \), HCl donates a proton to water, making HCl the acid and H2O the base. In another example, if ammonia reacts with water \( \text{NH}_3 + \text{H}_2\text{O} \rightarrow \text{NH}_4^+ + \text{OH}^- \), water acts as a proton donor (acid) and ammonia acts as a proton acceptor (base).

**Lewis Concept of Acid and Base:**
\( \implies \) **Acid:** A Lewis acid is defined as an electron pair acceptor. These often have empty orbitals to accept electron pairs.
\( \implies \) **Base:** A Lewis base is defined as an electron pair donor. These typically have lone pairs of electrons to donate.
For example, in the reaction between boron trifluoride (BF\( _3 \)) and ammonia (NH\( _3 \)), ammonia (with its lone pair of electrons) donates an electron pair to boron trifluoride (which has an empty orbital), forming an adduct. Thus, NH\( _3 \) is a Lewis base and BF\( _3 \) is a Lewis acid. This concept broadens the definition beyond proton transfer to include reactions without hydrogen.
In simple words: Brønsted-Lowry says acids give away protons and bases take them. Lewis says acids take electron pairs and bases give them away. These ideas help us understand how different chemicals react as acids and bases.

🎯 Exam Tip: Understand that the Lewis definition is the broadest acid-base concept, encompassing all Brønsted-Lowry acids and bases, and also including reactions that do not involve protons.

Question 33. What is the significance of pH in everyday life?
Answer: The importance of pH in everyday life is vast and affects many biological and environmental processes:
1. **Human Body Function:** Our bodies work best within a narrow pH range of 7.0 to 7.8. Any significant deviation can lead to serious health issues because enzymes and other biological processes are very sensitive to pH levels.
2. **Acid Rain:** Acid rain, which has a pH lower than 5.6, has detrimental effects on aquatic life. It harms fish and other organisms in lakes and rivers by changing their environment. Acid rain also damages buildings and plants.
3. **Soil pH and Plants:** Different plants require specific pH ranges in the soil to grow well. Farmers often test soil pH and adjust it using fertilizers or other substances to ensure optimal conditions for their crops.
4. **Digestion in Stomach:** The acids produced by our stomach, primarily hydrochloric acid, are crucial for proper digestion. They help break down food and kill harmful bacteria. If too much acid is produced (hyperacidity), people take antacids like milk of magnesia to neutralize the excess acid and relieve discomfort.
In simple words: pH is very important for our body, how plants grow in soil, and even for water life. Our body needs a certain pH, and too much acid (like in acid rain) can harm nature and digestion.

🎯 Exam Tip: When discussing the significance of pH, provide diverse examples from biology, agriculture, and environmental science to demonstrate a comprehensive understanding of its impact.

Question 34. Write the name, method of production and uses of following:
(i) NaOH
(ii) NaHCO3
(iii) Na2CO3.10H2O
(iv) CaOCl2
(v) CaSO4.1/2H2O
Answer:
(i) **Name:** Sodium hydroxide (Caustic soda)
**Method of Production:** It is produced by the chlor-alkali process, where an aqueous solution of sodium chloride (brine) is electrolyzed.
\( 2\text{NaCl (aq)} + 2\text{H}_2\text{O (l)} \xrightarrow{\text{electrolysis}} 2\text{NaOH (aq)} + \text{Cl}_2\text{ (g)} + \text{H}_2\text{ (g)} \)
**Uses:** It is used in making paper, soap, detergents, and artificial fibers.

(ii) **Name:** Sodium bicarbonate (Baking soda)
**Method of Production:** It is made by the reaction of sodium chloride, ammonia, carbon dioxide, and water (Solvay process).
\( \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 + \text{NH}_3 \rightarrow \text{NH}_4\text{Cl} + \text{NaHCO}_3 \)
**Uses:** It is used as an antacid, in soda-acid fire extinguishers, and in making baking powder.

(iii) **Name:** Sodium carbonate decahydrate (Washing soda)
**Method of Production:** When baking soda is heated, it produces sodium carbonate. This sodium carbonate is then crystallized by adding water to form washing soda.
\( 2\text{NaHCO}_3 \xrightarrow{\text{heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2 \)
\( \text{Na}_2\text{CO}_3 + 10\text{H}_2\text{O} \rightarrow \text{Na}_2\text{CO}_3.10\text{H}_2\text{O} \)
**Uses:** It is used in making glass, paper, soap, and borax. It is also used as a cleansing agent and for removing the permanent hardness of water.

(iv) **Name:** Calcium oxychloride (Bleaching powder)
**Method of Production:** It is made by the action of chlorine gas on dry slaked lime.
\( \text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O} \)
**Uses:** It is used for bleaching cotton, linen, and wood pulp. It acts as an oxidizing agent in the chemical industry and is used for disinfecting drinking water.

(v) **Name:** Calcium sulfate hemihydrate (Plaster of Paris)
**Method of Production:** It is prepared by heating gypsum (calcium sulfate dihydrate, \( \text{CaSO}_4.2\text{H}_2\text{O} \)) to about 373 K (100°C).
\( \text{CaSO}_4.2\text{H}_2\text{O} \xrightarrow{373\text{K}} \text{CaSO}_4.\frac{1}{2}\text{H}_2\text{O} + 1\frac{1}{2}\text{H}_2\text{O} \)
**Uses:** It is primarily used in hospitals for plaster casts to support fractured bones, in making toys, and for smoothing wall surfaces. It is also used for making decorative designs on ceilings.
In simple words: This answer lists five important chemicals: sodium hydroxide, sodium bicarbonate, washing soda, bleaching powder, and Plaster of Paris. For each, it explains how it is made and what it is used for in homes and industries.

🎯 Exam Tip: When answering questions about compounds, always include the chemical name, common name (if any), chemical formula, and at least two important uses. Balanced equations for their preparation are also crucial.

Question 35. Explain the formation and working of micelle.
Answer: Soap molecules have two distinct parts: a hydrophilic (water-loving) head and a hydrophobic (water-hating) long hydrocarbon tail.
\( \implies \) **Formation of Micelle:** When soap is dissolved in water, the hydrophobic (hydrocarbon) tails of the soap molecules try to avoid water. They gather together, pointing towards the center. The hydrophilic (ionic) heads, which are attracted to water, arrange themselves on the outer surface of this cluster, pointing outwards into the water. This spherical arrangement, with the hydrocarbon tails in the core and the ionic heads on the surface, is called a micelle.
\( \implies \) **Working of Micelle:** When a micelle forms in the presence of oily dirt or grease, the hydrophobic tails of the soap molecules penetrate and get dissolved in the oil droplet. The hydrophilic heads remain in contact with the water. Through agitation (like rubbing clothes), the tails effectively encapsulate the dirt, oil, or grease within the micelle. The negatively charged hydrophilic heads on the outer surface of the micelle repel other micelles, preventing them from clumping together. When the water is rinsed away, these stable, dirt-containing micelles are carried along with it, thus cleaning the clothes, utensils, or skin.
In simple words: Soap molecules have a head that loves water and a tail that hates it (but loves oil). In water, the tails hide inside, forming a ball called a micelle, with the heads outside. This micelle traps oil and dirt inside, then gets washed away with the water, cleaning things.

🎯 Exam Tip: A clear diagram illustrating the micelle structure, with labels for hydrophilic head, hydrophobic tail, and trapped dirt, can significantly enhance your explanation of its formation and cleaning action.

Chemistry in Everyday Life Additional Questions Solved

I. Multiple Choice Questions

Question 1. A milkman added a small pinch of baking soda to fresh milk which had pH close to 6. As a result, pH of the medium
(a) became close to 2
(b) became close to 4
(c) did not undergo any change
(d) became close to 8
Answer: (d) became close to 8
In simple words: Adding baking soda (which is a base) to milk makes it less acidic, so its pH will increase from 6 to a slightly basic value, like 8.

🎯 Exam Tip: Baking soda is sodium bicarbonate (\( \text{NaHCO}_3 \)), a mild base. Adding it to an acidic or neutral solution will always increase the pH, moving it towards the basic side of the scale.

Question 3. The compound used for neutralisation of excess HCl in the stomach is
(a) NaHCO3
(b) Mg(OH)2
(c) Both (a) and (b)
(d) None of the options
Answer: (c) Both (a) and (b)
In simple words: Both baking soda (sodium bicarbonate) and milk of magnesia (magnesium hydroxide) are mild bases used as antacids to neutralize too much stomach acid.

🎯 Exam Tip: Antacids are typically weak bases, which can neutralize excess stomach acid (HCl) without causing severe side effects. Common antacids include carbonates and hydroxides of certain metals.

Question 4. Which of the following is incorrectly matched?
(a) Tomato - tartaric acid
(b) Citrus - citric acid
(c) Ant sting - methanoic acid
(d) Curd - lactic acid
Answer: (a) Tomato - tartaric acid
In simple words: The incorrect match is tomato with tartaric acid. Tomatoes contain oxalic acid and citric acid, while tartaric acid is found in grapes and tamarind.

🎯 Exam Tip: Knowing which natural acids are present in common foods is important. For example, citric acid is in citrus fruits, lactic acid in dairy, and methanoic acid in ant stings.

Question 5. A solution reacts with crushed egg shells to give a gas that turns lime water milky. The solution contains
(a) NaCl
(b) HCl
(c) LiCl
(d) KCl
Answer: (b) HCl
In simple words: Egg shells are mainly calcium carbonate. If a solution reacts with them to make a gas that turns lime water milky, it means the gas is carbon dioxide, which is produced when an acid (like HCl) reacts with a carbonate.

🎯 Exam Tip: The reaction of an acid with a carbonate always produces carbon dioxide gas. The "lime water test" (turning milky) is the standard test for identifying carbon dioxide.

Question 6. Which of the following salt will have OH\(^-\) ions when dissolved in water?
(a) NH4Cl
(b) NaCl
(c) CH3COONa
(d) Na2SO4
Answer: (c) CH3COONa
In simple words: When sodium acetate (\( \text{CH}_3\text{COONa} \)) dissolves in water, it creates hydroxide ions (OH\(^-\)). This happens because it is a salt of a weak acid (acetic acid) and a strong base (sodium hydroxide), leading to hydrolysis that makes the solution slightly basic.

🎯 Exam Tip: Salts formed from a strong base and a weak acid will hydrolyze in water to produce hydroxide ions, making the solution basic. Conversely, salts of a strong acid and a weak base will produce hydrogen ions, making the solution acidic.

Question 7. Which of the following gives the correct increasing order of acidic strength?
(a) Water < Acetic acid < Hydrochloric acid
(b) Water < Hydrochloric acid < Acetic Acid
(c) Acetic acid < Water < Hydrochloric acid
(d) Hydrochloric acid < Water < Acetic Acid
Answer: (a) Water < Acetic acid < Hydrochloric acid
In simple words: Water is the least acidic, acetic acid is a weak acid, and hydrochloric acid is a strong acid. So, their acidic strength increases in that order.

🎯 Exam Tip: Remember that strong acids ionize completely in water, while weak acids only ionize partially. Water itself is amphoteric but has a very low degree of self-ionization, making it very weakly acidic.

Question 8. Which of the following phenomenon occur when a small amount of acid is added to water?
(i) Ionisation
(ii) Dilution
(iii) Neutralisation
(iv) Salt formation
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer: (a) (i) and (ii)
In simple words: When a little acid is added to water, the acid will ionize (break into ions) and also get diluted (spread out in the water).

🎯 Exam Tip: Adding acid to water causes both ionization (release of H+ ions) and dilution (reduction in concentration). Neutralization and salt formation only occur if a base is also present.

Question 9. Identify the correct representation of reaction occurring during chlor-alkali process.
(a) \( \text{NaCl (aq)} + \text{H}_2\text{O (l)} \rightarrow \text{NaOH (aq)} + \text{Cl}_2\text{ (g)} + \text{H}_2\text{ (g)} \)
(b) \( 2\text{NaCl (aq)} + \text{H}_2\text{O (l)} \rightarrow 2\text{NaOH (aq)} + \text{Cl}_2\text{ (g)} + \text{H}_2\text{ (g)} \)
(c) \( 2\text{NaCl (aq)} + 2\text{H}_2\text{O (l)} \rightarrow 2\text{NaOH (aq)} + \text{Cl}_2\text{ (g)} + 2\text{H}_2\text{ (g)} \)
(d) \( 2\text{NaCl (aq)} + 2\text{H}_2\text{O (l)} \rightarrow 2\text{NaOH (aq)} + \text{Cl}_2\text{ (g)} + \text{H}_2\text{ (g)} \)
Answer: (d) 2NaCl(aq) + 2H2O(l) \( \rightarrow \) 2NaOH(aq) + Cl2(g) + H2(g)
In simple words: The chlor-alkali process involves passing electricity through saltwater (brine) to make sodium hydroxide, chlorine gas, and hydrogen gas. The balanced equation shows the correct amounts of each substance.

🎯 Exam Tip: Always ensure the chemical equation is balanced, meaning the number of atoms of each element is the same on both sides of the reaction. This is fundamental to chemical stoichiometry.

Question 10. The chemical formula of caustic potash is
(a) NaOH
(b) Ca(OH)2
(c) NH4OH
(d) KOH
Answer: (d) KOH
In simple words: Caustic potash is the common name for potassium hydroxide, which has the chemical formula KOH. It is a strong base.

🎯 Exam Tip: Remember common names for important chemicals like 'caustic potash' for KOH and 'caustic soda' for NaOH. This helps avoid confusion between similar compounds.

Question 11. Substances exposed to atmosphere at ordinary temperature, lose their water of crystallisation are called as
(a) hygroscopic
(b) efflorescent
(c) deliquescent
(d) all of the options
Answer: (b) efflorescent
In simple words: Efflorescent substances are those that give up their water of crystallization to the air when kept at normal room temperature. This causes them to become powdery.

🎯 Exam Tip: Distinguish between efflorescence (losing water of crystallization), deliquescence (absorbing moisture from the air to form a solution), and hygroscopy (absorbing moisture without forming a solution).

Question 12. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Antacid
(c) Analgesic
(d) Antiseptic
Answer: (b) Antacid
In simple words: Antacids are medicines that help indigestion by neutralizing the extra acid in your stomach, making you feel better.

🎯 Exam Tip: Each type of medicine has a specific function: antibiotics fight bacteria, analgesics relieve pain, and antiseptics kill germs on surfaces. Antacids are specifically for acid-related issues.

Question 14. An element 'X' forms a solid oxide which dissolves in water forming solution which turns blue litmus paper red, 'X' is
(a) Ca
(b) Cu
(c) Fe
(d) P
Answer: (d) P
In simple words: 'X' is a substance that forms a solid oxide. When this oxide dissolves in water, the solution becomes acidic, meaning it turns blue litmus paper red. This kind of substance is phosphorus.

🎯 Exam Tip: Remember that oxides of non-metals are typically acidic, while oxides of metals are generally basic. Non-metals turn blue litmus red in solution.

Question 15. The formula of washing soda is
(a) NaHCO3
(b) Na2CO3. H₂O
(c) Na₂CO₃
(d) Na2CO3.10H2O
Answer: (d) Na2CO3.10H2O
In simple words: Washing soda's chemical formula shows it has sodium carbonate and ten water molecules attached. This specific hydration makes it washing soda.

🎯 Exam Tip: Be careful not to confuse the formula of washing soda with baking soda (NaHCO₃) or anhydrous sodium carbonate (Na₂CO₃).

Question 16. The substance which on treating with chlorine, yields bleaching powder is
(a) quick lime
(b) limestone
(c) slaked lime
(d) gypsum
Answer: (c) slaked lime
In simple words: Slaked lime reacts with chlorine gas to make bleaching powder. This reaction is important for producing disinfectants.

🎯 Exam Tip: Know the difference between quick lime (CaO), slaked lime (Ca(OH)₂), and limestone (CaCO₃) and their roles in chemical reactions.

Question 18. An aqueous solution has [H+] ion concentration = 1.0 x 10-7mol¯¹. Its pH value is
(a) +7
(b) -7
(c) 0.70
(d) 10-7
Answer: (a) +7
In simple words: pH tells us how acidic or basic a solution is. When the hydrogen ion amount is \( 1.0 \times 10^{-7} \), the pH is 7. A pH of 7 means the solution is neutral.

🎯 Exam Tip: Remember that pH is defined as \( -\log[\text{H}^+] \). For \( [\text{H}^+] = 10^{-7} \), the pH is \( -(\text{-}7) = 7 \).

Question 19. Milk of magnesia is
(a) solid magnesium oxide
(b) solid magnesium hydroxide
(c) suspension of magnesium hydroxide
(d) insoluble magnesium carbonate
Answer: (c) suspension of magnesium hydroxide
In simple words: Milk of magnesia is just tiny bits of magnesium hydroxide floating in water, which gives it a milky look. It works as an antacid to relieve indigestion.

🎯 Exam Tip: Understand the difference between a solution, colloid, and suspension. Milk of magnesia is a suspension because its particles are large enough to settle over time.

Question 20. The pH of human blood varies between
(a) 4 to 5.5
(b) 7 to 7.8
(c) 5 to 6.2
(d) 9 to 10.2
Answer: (b) 7 to 7.8
In simple words: Human blood needs to stay at a pH between 7.0 and 7.8 for the body to work well. This narrow range is critical for maintaining overall health.

🎯 Exam Tip: The body has buffer systems to maintain this crucial pH range in blood. Deviations can be life-threatening.

Question 22. Calcium phosphate is present in tooth enamel, its nature is
(a) basic
(b) amphoteric
(c) acidic
(d) neutral
Answer: (a) basic
In simple words: Our tooth enamel is made of calcium phosphate, which is basic. This basic nature helps it to resist mild acids.

🎯 Exam Tip: Tooth enamel is mostly hydroxyapatite, a form of calcium phosphate. Its basic nature makes it susceptible to dissolution by acids, leading to tooth decay.

Question 23. Which of the following salts does not contain any water of crystallisation?
(a) Blue vitriol
(b) Washing soda
(c) Baking soda
(d) Gypsum
Answer: (c) Baking soda
In simple words: Baking soda is a salt that does not naturally have water molecules as part of its crystal structure, unlike some other salts. Water of crystallisation is essential for the crystal shape of many salts.

🎯 Exam Tip: Know the chemical formulas for common salts like blue vitriol (\( \text{CuSO}_4 \cdot 5\text{H}_2\text{O} \)), washing soda (\( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \)), baking soda (\( \text{NaHCO}_3 \)), and gypsum (\( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \)).

Question 24. A sample of soil is mixed with water and allowed to settle. The clear suspended solution turns the pH paper yellowish- orange. Which of the following would change the colour of this pH paper to greenish-blue?
(a) Lemon juice
(b) An antacid
(c) Typesetting math: 66%
Answer: (b) An antacid
In simple words: The soil solution is acidic because it turns pH paper yellowish-orange. To make it greenish-blue (basic), we need to add something basic, like an antacid. Lemon juice would make it even more acidic.

🎯 Exam Tip: Recall the pH scale and corresponding colors for pH paper: acidic (red-orange-yellow), neutral (green), basic (blue-purple). To shift an acidic solution towards basic, a basic substance must be added.

Question 26. The difference of molecules of water in gypsum and Plaster of Paris is
(a) 5/2
(b) 2
(c) 3/2
(d) 1/2
Answer: (c) 3/2
In simple words: Gypsum has 2 water molecules, and Plaster of Paris has 0.5 water molecules. The difference between them is 1.5, or \( \frac{3}{2} \). This difference is key to how Plaster of Paris hardens.

🎯 Exam Tip: Remember the formulas: Gypsum is \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \) and Plaster of Paris is \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \). The question asks for the difference in the number of water molecules.

Question 27. Which of the following does not form an acidic salt?
(a) Phosphoric acid
(b) Carbonic acid
(c) Hydrochloric acid
(d) Sulphuric acid
Answer: (b) Carbonic
In simple words: Carbonic acid is a weak acid. Unlike strong acids such as hydrochloric or sulfuric acid, it generally does not form salts that are acidic in solution; its salts are often basic due to hydrolysis.

🎯 Exam Tip: Acidic salts typically form from a strong acid and a weak base, or from the partial neutralization of a polyprotic acid where the remaining hydrogen ions contribute to acidity. Carbonic acid is a weak acid, and its salts often hydrolyze to produce basic solutions.

Chemistry in Everyday Life Very Short Answer Type Questions

Question 1. What is an acid?
Answer: An acid is a substance that typically tastes sour and turns blue litmus paper red. In chemistry, acids are known to release hydrogen ions (\( \text{H}^+ \)) when dissolved in water, which is why they are corrosive. This property defines their chemical behavior.
In simple words: An acid is a substance that tastes sour and can change blue litmus paper to red.

🎯 Exam Tip: Always include both observational properties (taste/litmus color) and chemical definitions (release of \( \text{H}^+ \) ions) when defining an acid.

Question 3. Which acid is secreted in stomach?
Answer: The human stomach produces hydrochloric acid. This strong acid helps in the digestion of food by breaking it down and also kills harmful bacteria that enter the body with food, providing a protective barrier.
In simple words: Hydrochloric acid is the acid made in our stomach.

🎯 Exam Tip: Remember that the stomach's inner lining is protected by a thick layer of mucus to prevent damage from this strong acid.

Question 4. Which acid is present in vinegar?
Answer: Acetic acid is the main acid found in vinegar. It is responsible for vinegar's characteristic sour taste and pungent smell, and it is a common ingredient in cooking and cleaning products.
In simple words: Vinegar contains acetic acid, which gives it its sour taste.

🎯 Exam Tip: Acetic acid is a weak organic acid, often represented as \( \text{CH}_3\text{COOH} \).

Question 5. Which ions are released by aqueous solution of acid?
Answer: When an acid is dissolved in water, it releases hydrogen ions (\( \text{H}^+ \)). These hydrogen ions then combine with water molecules to form hydronium ions (\( \text{H}_3\text{O}^+ \)), which are actually responsible for the acidic properties of the solution.
In simple words: Acids release hydrogen ions when mixed with water.

🎯 Exam Tip: While \( \text{H}^+ \) is often used, remember that in water, it's more accurately represented as \( \text{H}_3\text{O}^+ \).

Question 6. Which ions are released by aqueous solution of base?
Answer: When a base is dissolved in water, it releases hydroxide ions (\( \text{OH}^- \)). These ions are responsible for the basic or alkaline properties of the solution, such as a slippery feel and bitter taste.
In simple words: Bases release hydroxide ions when mixed with water.

🎯 Exam Tip: The presence of \( \text{OH}^- \) ions is what characterizes an aqueous basic solution according to the Arrhenius definition.

Question 7. What is the pH of distilled water?
Answer: Distilled water is pure water that has been processed to remove impurities and minerals. Because it is neutral, meaning it is neither acidic nor basic, its pH value is exactly 7. This is the midpoint of the pH scale.
In simple words: Pure distilled water has a pH of 7 because it is neutral.

🎯 Exam Tip: Even slightly contaminated water (e.g., tap water with dissolved minerals or \( \text{CO}_2 \)) may not have an exact pH of 7.

Question 8. What is a strong acid?
Answer: A strong acid is an acid that completely ionizes or dissociates in water, meaning it releases a very high concentration of hydrogen ions (\( \text{H}^+ \)). This high concentration of hydrogen ions makes the solution very acidic and highly reactive. Examples include hydrochloric acid and sulfuric acid.
In simple words: A strong acid releases a lot of hydrogen ions when it dissolves in water.

🎯 Exam Tip: Complete ionization is the key characteristic of a strong acid, distinguishing it from a weak acid that only partially ionizes.

Chemistry in Everyday Life Short Answer Type Questions

Question 1. A white powder which sets hard on adding water is also used in hospitals. Name this powder. How is it prepared? Write the chemical reaction involved in its preparation.
Answer: The white powder that hardens when mixed with water and is used in hospitals is Plaster of Paris (POP). Its chemical formula is \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \). Plaster of Paris is made by heating gypsum (\( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \)) to a temperature of 373 Kelvin. During this heating, gypsum loses three-quarters of its water molecules, leading to the formation of POP.
\[ \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \xrightarrow{\text{heat at } 373\text{ K}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + \frac{3}{2}\text{H}_2\text{O} \]
In simple words: The white powder is Plaster of Paris. We make it by heating gypsum at 373 K. This heating takes away most of the water from gypsum.

🎯 Exam Tip: Pay attention to the specific temperature and the exact amount of water lost (or remaining) when writing the preparation of Plaster of Paris.

Question 2. Write balanced chemical equations for the following: (a) Calcium carbonate reacts with hydrochloric acid (b) Dilute sulphuric acid reacts with zinc granules (c) Calcium oxychloride reacts with hydrochloric acid.
Answer: Here are the balanced chemical equations for the given reactions. These equations show how atoms rearrange to form new substances, ensuring mass is conserved.
(a) Calcium carbonate reacts with hydrochloric acid:
\[ \text{CaCO}_3 \text{(s)} + 2\text{HCl} \text{(aq)} \rightarrow \text{CaCl}_2 \text{(aq)} + \text{H}_2\text{O} \text{(l)} + \text{CO}_2 \text{(g)} \]
(b) Dilute sulfuric acid reacts with zinc granules:
\[ \text{H}_2\text{SO}_4 \text{(aq)} + \text{Zn} \text{(s)} \rightarrow \text{ZnSO}_4 \text{(aq)} + \text{H}_2 \text{(g)} \]
(c) Calcium oxychloride reacts with hydrochloric acid:
\[ \text{CaOCl}_2 \text{(s)} + 2\text{HCl} \text{(aq)} \rightarrow \text{CaCl}_2 \text{(aq)} + \text{H}_2\text{O} \text{(l)} + \text{Cl}_2 \text{(g)} \]
In simple words:
(a) Calcium carbonate and hydrochloric acid make calcium chloride, water, and carbon dioxide.
(b) Sulfuric acid and zinc make zinc sulfate and hydrogen gas.
(c) Calcium oxychloride and hydrochloric acid make calcium chloride, water, and chlorine gas.

🎯 Exam Tip: Always ensure chemical equations are balanced, meaning the number of atoms of each element is the same on both sides of the reaction. Include state symbols for clarity.

Question 3. Name the ions present in the following salts. Name the acid and base from which they can be obtained. magnesium sulphate, sodium carbonate, potassium chloride.
Answer: Salts are formed from the reaction of an acid and a base. Each salt can be broken down into its constituent positive and negative ions. For magnesium sulfate, sodium carbonate, and potassium chloride, their ions and the parent acid and base are as follows:

In simple words: We can find the parts (ions) of each salt and also see which acid and base they came from. Knowing this helps us understand how salts are formed.

🎯 Exam Tip: To identify the parent acid and base, separate the positive ion (cation) from the negative ion (anion). The cation usually comes from the base (e.g., \( \text{Na}^+ \) from \( \text{NaOH} \)), and the anion comes from the acid (e.g., \( \text{Cl}^- \) from \( \text{HCl} \)).

Question 4. Give three ways in which salts can be prepared.
Answer: Salts can be prepared through several types of chemical reactions. Three common methods include:
(i) **Reaction of an Acid with a Base (Neutralization Reaction):** When an acid reacts with a base, it undergoes a neutralization reaction to produce a salt and water.
Example: \( \text{HCl} \text{(aq)} + \text{KOH} \text{(aq)} \rightarrow \text{KCl} \text{(aq)} + \text{H}_2\text{O} \text{(l)} \)
(ii) **Reaction of a Metal with an Acid:** Many active metals react directly with acids to form a salt and release hydrogen gas.
Example: \( \text{Mg} \text{(s)} + 2\text{HCl} \text{(aq)} \rightarrow \text{MgCl}_2 \text{(aq)} + \text{H}_2 \text{(g)} \)
(iii) **Reaction of a Metallic Oxide with an Acid:** Metallic oxides, which are basic in nature, react with acids to produce a salt and water.
Example: \( \text{CuO} \text{(s)} + 2\text{HCl} \text{(aq)} \rightarrow \text{CuCl}_2 \text{(aq)} + \text{H}_2\text{O} \text{(l)} \)
In simple words: We can make salts in three main ways: by mixing an acid and a base, by reacting a metal with an acid, or by reacting a metal oxide with an acid.

🎯 Exam Tip: For each method, provide a clear, balanced chemical equation to illustrate the preparation of a specific salt. Understanding these general reaction types helps predict products.

Question 5. Give two examples for each of the following acids salts – chloride salts, nitrate salts and sulphate salts.
Answer: Different types of salts are named based on the acid from which they are derived. Here are two examples for each category:
(i) **Chloride Salts:** These are derived from hydrochloric acid (\( \text{HCl} \)). Examples include magnesium chloride (\( \text{MgCl}_2 \)) and calcium chloride (\( \text{CaCl}_2 \)).
(ii) **Nitrate Salts:** These are formed from nitric acid (\( \text{HNO}_3 \)). Examples include ammonium nitrate (\( \text{NH}_4\text{NO}_3 \)) and aluminum nitrate (\( \text{Al(NO}_3)_3 \)).
(iii) **Sulphate Salts:** These come from sulfuric acid (\( \text{H}_2\text{SO}_4 \)). Examples are calcium sulfate (\( \text{CaSO}_4 \)) and magnesium sulfate (\( \text{MgSO}_4 \)).
In simple words: Here are two examples for each kind of salt: chloride salts (magnesium chloride, calcium chloride), nitrate salts (ammonium nitrate, aluminum nitrate), and sulphate salts (calcium sulfate, magnesium sulfate).

🎯 Exam Tip: Learn the common strong acids (HCl, HNO₃, H₂SO₄) and their corresponding salt types (chlorides, nitrates, sulfates). This helps in naming and classification.

Question 6. Name the acid present in the following: Vinegar, Lemon, Tomato, Tamarind, Orange, Curd.
Answer: Different natural substances contain specific types of organic acids which contribute to their flavor and properties. Knowing these helps understand their chemical nature.

In simple words: Many foods have natural acids. For example, vinegar has acetic acid, lemon has citric acid, and curd has lactic acid.

🎯 Exam Tip: Memorize the common organic acids found in everyday food items. This is a frequently asked general knowledge question in science.

Question 7. Name the properties responsible for the following uses of baking powder: (i) Baking industry (ii) As an antacid (iii) As soda-acid fire extinguisher
Answer: Baking powder is a versatile substance due to its distinct chemical properties, which make it useful in various applications:
(i) **Baking Industry:** Baking powder contains sodium bicarbonate which, upon heating or reaction with liquid, releases carbon dioxide gas. This property is crucial for making baked goods rise and become fluffy.
(ii) **As an Antacid:** Baking powder contains sodium bicarbonate, which is alkaline (basic) in nature. This property allows it to neutralize excess acid in the stomach, providing relief from indigestion.
(iii) **As a Soda-Acid Fire Extinguisher:** When baking powder reacts with an acid, it rapidly releases a large amount of carbon dioxide gas. This dense gas smothers fires by cutting off their oxygen supply, making it effective in fire extinguishers.
In simple words: Baking powder is useful because of these reasons: (i) In baking, it makes carbon dioxide gas when heated, which helps food rise. (ii) As an antacid, it is basic and can calm down extra stomach acid. (iii) In fire extinguishers, it makes carbon dioxide gas when mixed with acid, which helps put out fires.

🎯 Exam Tip: Focus on the chemical reactions involved in each use: decomposition producing \( \text{CO}_2 \) for baking and fire extinguishing, and neutralization for antacid action.

Question 8. Give the properties and uses of bleaching powder.
Answer: Bleaching powder is chemically known as calcium oxychloride, with the formula \( \text{CaOCl}_2 \). It is a powerful chemical with several key properties and uses. When it reacts with dilute acids, it releases chlorine gas. This chlorine then reacts with water to produce nascent oxygen, a highly reactive form of oxygen responsible for its bleaching action.
Its uses are:
(i) **Bleaching Agent:** It is widely used in the textile industry to bleach cotton and linen, and in paper factories to bleach wood pulp, giving them a clean, white appearance.
(ii) **Oxidizing Agent:** Due to its ability to release oxygen, it acts as an effective oxidizing agent in many chemical industries, facilitating various chemical reactions.
(iii) **Disinfectant:** It is used to disinfect drinking water, making it free from germs and safe for consumption by killing harmful microorganisms.
In simple words: Bleaching powder creates chlorine gas when it meets acid, and this gas helps it bleach things. It is used to bleach cotton and paper, as a helper chemical in industries, and to clean drinking water by killing germs.

🎯 Exam Tip: Remember both the chemical formula and the three main applications of bleaching powder, connecting them to its property as an oxidizing agent.

Question 9. Acid when reacts with metal release hydrogen gas but there is one acid which when reacts with metal does not release hydrogen except for two metals. Prove this statement.
Answer: Generally, acids react with active metals to produce hydrogen gas. However, nitric acid (\( \text{HNO}_3 \)) is an exception because it is a very strong oxidizing agent. When nitric acid reacts with most metals, it oxidizes the hydrogen produced into water, and instead, produces oxides of nitrogen. The only metals that react with very dilute nitric acid to produce hydrogen gas are magnesium (\( \text{Mg} \)) and manganese (\( \text{Mn} \)). This specific behavior is due to nitric acid's strong oxidizing nature.
Examples of reactions releasing hydrogen gas:
\( \text{Mg} \text{(s)} + 2\text{HNO}_3 \text{(dilute)} \rightarrow \text{Mg(NO}_3)_2 \text{(aq)} + \text{H}_2 \text{(g)} \)
\( \text{Mn} \text{(s)} + 2\text{HNO}_3 \text{(dilute)} \rightarrow \text{Mn(NO}_3)_2 \text{(aq)} + \text{H}_2 \text{(g)} \)
In simple words: Most acids and metals make hydrogen gas. But nitric acid is special because it usually turns the hydrogen into water. Only magnesium and manganese metals can make hydrogen gas when reacting with very weak nitric acid.

🎯 Exam Tip: This is a common exception to the general rule of acid-metal reactions. Highlight the oxidizing property of nitric acid as the reason for this unusual behavior.

Question 10. Give six uses of acids.
Answer: Acids are fundamental substances with a wide range of practical applications in daily life and industries. Here are six significant uses:
(i) **Storage Batteries:** Sulfuric acid (\( \text{H}_2\text{SO}_4 \)) is a key electrolyte in car batteries and other lead-acid storage batteries, enabling them to store electrical energy.
(ii) **Food Preservative:** Acetic acid, commonly found in vinegar, is used to preserve foods like pickles and sauces by inhibiting microbial growth.
(iii) **Baking Powder:** Tartaric acid is an essential component of baking powder, reacting to produce carbon dioxide and help dough rise, creating light and airy baked goods.
(iv) **Fertilizer Manufacturing:** Nitric acid is crucial in the production of various nitrogen-based fertilizers, essential for agricultural productivity.
(v) **PVC Production:** Hydrochloric acid is used in the synthesis of polyvinyl chloride (PVC), a widely used plastic in pipes, window frames, and more.
(vi) **Bathroom Cleaner:** Hydrochloric acid is an effective ingredient in many bathroom cleaners due to its ability to dissolve mineral deposits and tough stains, such as limescale.
In simple words: Acids are used for many things: (i) Sulfuric acid helps car batteries work. (ii) Acetic acid keeps food from spoiling. (iii) Tartaric acid helps baking powder make cakes fluffy. (iv) Nitric acid is used to make fertilizers for plants. (v) Hydrochloric acid helps make PVC plastic. (vi) Hydrochloric acid cleans bathrooms.

🎯 Exam Tip: When listing uses, try to give a specific acid as an example for each use to demonstrate comprehensive knowledge.

Question 11. Give six uses of bases.
Answer: Bases also have numerous applications across different sectors due to their unique chemical properties, often related to their ability to neutralize acids or react with certain substances. Here are six uses:
(i) **Soap Making:** Sodium hydroxide (\( \text{NaOH} \)), also known as caustic soda, is a vital ingredient in the saponification process for making soap from fats and oils.
(ii) **Antacids:** Magnesium hydroxide (\( \text{Mg(OH)}_2 \)) is a common active ingredient in antacids, used to relieve indigestion by neutralizing excess stomach acid.
(iii) **Bleaching Powder Production:** Calcium hydroxide (\( \text{Ca(OH)}_2 \)), or slaked lime, is used in the manufacturing of bleaching powder, an important disinfectant and bleaching agent.
(iv) **Soil Treatment:** Calcium hydroxide is applied to agricultural soils to reduce excessive acidity, creating better conditions for crop growth and improving soil structure.
(v) **Whitewashing:** Calcium hydroxide is traditionally used for whitewashing walls, providing a protective and bright coating that also acts as a disinfectant.
(vi) **Fertilizer Production:** Ammonium hydroxide (\( \text{NH}_4\text{OH} \)) is used in the production of certain nitrogen-based fertilizers, supplying essential nutrients to plants.
In simple words: Bases are used for many things: (i) Sodium hydroxide is used to make soap. (ii) Magnesium hydroxide helps as an antacid for stomach problems. (iii) Calcium hydroxide is used to make bleaching powder. (iv) Calcium hydroxide helps reduce too much acid in soil. (v) Calcium hydroxide is used for painting walls white. (vi) Ammonium hydroxide is used to make fertilizers.

🎯 Exam Tip: Similar to acids, try to associate a specific base with each use to provide a more complete answer.

Question 13. Four samples A, B, C and D were given to test their nature. A student found the change in pH paper as follows: A → green colour C→ blue colour B → orange colour D→ pink colour Find the nature of given sample.
Answer: A student tested four different samples (A, B, C, and D) using pH paper to determine their acidic or basic nature. The color changes observed on the pH paper correspond to specific pH values and the nature of the solution:

In simple words: A student used pH paper to check four samples. Green means neutral (pH 7). Orange means weak acid (pH 4). Blue means base (pH 9). Pink means strong acid (pH 2).

🎯 Exam Tip: Knowing the approximate pH ranges for different colors on universal indicator or pH paper is essential for identifying the nature of solutions.

Question 14. How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?
Answer: When hydrochloric acid reacts with an active metal, it produces hydrogen gas. To test for this gas, a simple method involves bringing a burning splinter (a small piece of wood or matchstick) near the mouth of the test tube where the gas is being released. If hydrogen gas is present, the splinter will extinguish with a characteristic "pop" sound. This "pop" sound is a unique indicator of hydrogen gas, confirming its presence.
In simple words: When hydrochloric acid reacts with an active metal, hydrogen gas comes out. To test for it, hold a burning match near the gas. If you hear a "pop" sound, it's hydrogen gas.

🎯 Exam Tip: The "pop" sound test is specific for hydrogen gas. Always perform this test carefully, avoiding inhaling the gas or holding the splinter too close to the source to prevent potential hazards.

Question 15. What is the role of baking powder in making a cake soft and spongy?
Answer: Baking powder is a mixture that releases carbon dioxide gas when it reacts with liquid and heat during baking. These gas bubbles get trapped in the dough, causing it to rise and become light. This process ensures the cake turns out soft and spongy. The tartaric acid in baking powder neutralizes the bitter taste of sodium carbonate produced, ensuring good flavor as well.
In simple words: Baking powder makes cakes soft and spongy by releasing carbon dioxide gas when it gets wet and heated. This gas creates tiny bubbles that make the cake light and fluffy.

🎯 Exam Tip: Emphasize the role of carbon dioxide gas in leavening (making dough rise) and the importance of the acidic component in baking powder to counteract bitterness.

Question 16. Fresh milk has a pH of 6. When it changes into curd (yogurt) will its pH value increase or decrease? Why?
Answer: When fresh milk, which typically has a pH of 6, transforms into curd (yogurt), its pH value will decrease, becoming more acidic. This change happens because bacteria present in the milk convert lactose sugar into lactic acid during the fermentation process. The production of lactic acid lowers the overall pH of the milk, turning it into curd and giving it a sour taste.
In simple words: When milk turns into curd, its pH goes down. This is because bacteria make lactic acid, which makes the curd more acidic than milk.

🎯 Exam Tip: Relate the change in pH to the formation of lactic acid. Lower pH means higher acidity.

Question 17. A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound. Write the chemical equation for its preparation. For what purpose is it used in hospitals?
Answer: The compound described is calcium sulfate hemihydrate, commonly known as Plaster of Paris (POP). It is prepared by heating gypsum (\( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \)) at a temperature of 373 Kelvin, which causes it to lose a specific amount of its water of crystallization.
The chemical equation for its preparation is:
\[ \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \xrightarrow{\text{heat at } 373\text{ K}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + \frac{3}{2}\text{H}_2\text{O} \]
In hospitals, Plaster of Paris is primarily used for setting fractured bones. When mixed with water, it quickly forms a solid, hard mass that immobilizes the injured limb, aiding in healing and proper bone alignment.
In simple words: The compound is Plaster of Paris. It is made by heating gypsum to 373 K, which removes some water. In hospitals, it is used to make casts for broken bones to help them heal.

🎯 Exam Tip: Ensure you remember both the specific temperature for preparation and the precise chemical formulas for gypsum and Plaster of Paris.

Question 18. (a) Give Arrhenius definition of an acid and a base. (b) Choose strong acid and strong base from the following: CH3COOH, NH4OH, KOH, HСІ
Answer:
(a) According to the Arrhenius concept, an acid is a substance that produces hydrogen ions (\( \text{H}^+ \)) when dissolved in water. Conversely, an Arrhenius base is a substance that produces hydroxide ions (\( \text{OH}^- \)) when dissolved in water. This theory focuses on the ions released in aqueous solutions.
(b) From the given list (CH₃COOH, NH₄OH, KOH, HCl), the strong acid is hydrochloric acid (\( \text{HCl} \)), and the strong base is potassium hydroxide (\( \text{KOH} \)). Acetic acid (\( \text{CH}_3\text{COOH} \)) is a weak acid, and ammonium hydroxide (\( \text{NH}_4\text{OH} \)) is a weak base.
In simple words:
(a) Arrhenius said acids make \( \text{H}^+ \) ions in water, and bases make \( \text{OH}^- \) ions in water.
(b) From the list, \( \text{HCl} \) is the strong acid and \( \text{KOH} \) is the strong base.

🎯 Exam Tip: Differentiate between strong and weak acids/bases by their extent of ionization in water (complete for strong, partial for weak).

Question 20. Name the gas evolved when dilute HCl reacts with sodium hydrogen carbonate. How is it recognised?
Answer: When dilute hydrochloric acid reacts with sodium hydrogen carbonate (baking soda), carbon dioxide gas (\( \text{CO}_2 \)) is evolved. This gas can be recognized by passing it through freshly prepared lime water (calcium hydroxide solution). The carbon dioxide reacts with the lime water to form insoluble calcium carbonate, which turns the clear lime water milky, providing a clear visual test.
The chemical reaction for this test is:
\( \text{Ca(OH)}_2 \text{(aq)} + \text{CO}_2 \text{(g)} \rightarrow \text{CaCO}_3 \text{(s)} + \text{H}_2\text{O} \text{(l)} \)
In simple words: When dilute \( \text{HCl} \) mixes with sodium hydrogen carbonate, carbon dioxide gas comes out. To test for it, bubble the gas through lime water. If the lime water turns milky, it means carbon dioxide is present.

🎯 Exam Tip: The lime water test (turning milky due to \( \text{CaCO}_3 \) formation) is the definitive test for carbon dioxide gas. Remember to mention "freshly prepared" lime water.

Question 21. How is the pH of a solution of an acid influenced when it is diluted?
Answer: When an acid solution is diluted by adding water, the concentration of hydrogen ions (\( \text{H}^+ \)) in moles per liter decreases. This reduction in \( \text{H}^+ \) ion concentration causes the pH value of the solution to increase. As the pH increases, the solution becomes less acidic, moving closer to a neutral pH of 7. The total amount of acid remains the same, but it's spread out in more water.
In simple words: When you add water to an acid, the amount of hydrogen ions goes down. This makes the pH number go up, and the acid becomes weaker.

🎯 Exam Tip: Remember the inverse relationship between \( [\text{H}^+] \) and pH: as \( [\text{H}^+] \) decreases, pH increases. For an acid, increasing pH means becoming less acidic.

Question 22. How does the pH of the solution change when a solution of base is diluted?
Answer: When a solution of a base is diluted by adding water, its concentration of hydroxide ions (\( \text{OH}^- \)) decreases. This means the solution becomes less basic (or less alkaline), and consequently, its pH value decreases, moving closer to a neutral pH of 7. For example, a strong base with a pH of 14 will have its pH drop below 14 upon dilution, becoming less alkaline.
In simple words: When you add water to a base, it becomes less basic. So, its pH number goes down, moving closer to 7.

🎯 Exam Tip: Understand the relationship between \( [\text{OH}^-] \), basicity, and pH. As \( [\text{OH}^-] \) decreases, basicity decreases, and pH decreases.

Question 23. Arrange the following in increasing order of their pH values: NaOH solution, blood, lemon juice.
Answer: To arrange these substances in increasing order of their pH values, we need to know their typical pH ranges:
* **Lemon juice** is highly acidic, with a typical pH of around 2-3.
* **Blood** is slightly basic, maintaining a very narrow and critical pH of about 7.35-7.45.
* **NaOH solution** (sodium hydroxide) is a strong base, typically having a very high pH, often 13-14, indicating strong alkalinity.
Therefore, the increasing order of pH is:
Lemon juice < Blood < NaOH solution.
In simple words: In order of increasing pH (from most acidic to most basic), the substances are: lemon juice (acidic), blood (slightly basic), and then \( \text{NaOH} \) solution (very basic).

🎯 Exam Tip: Familiarize yourself with the approximate pH values of common substances. This helps in understanding acidity/basicity in everyday contexts.

Question 25. Why does tooth decay start when the pH of mouth is lower than 5.5?
Answer: Tooth decay begins when the pH in the mouth drops below 5.5. This low pH indicates an increase in acidity, primarily caused by bacteria metabolizing food particles left on teeth and producing acids. These acids then react with and dissolve the tooth enamel, which is largely composed of calcium phosphate. This process of enamel erosion, called demineralization, is what initiates tooth decay.
In simple words: Tooth decay starts when your mouth's pH drops below 5.5. This happens because bacteria make acids from leftover food. These acids then eat away at your tooth enamel, which is made of calcium phosphate.

🎯 Exam Tip: The critical pH for tooth enamel demineralization is approximately 5.5. Below this, acids start dissolving the enamel.

Question 26. Which of these has a higher concentration of H+ ions – 1 M HCl or 1M CH3COOH?
Answer: A 1 M solution of hydrochloric acid (\( \text{HCl} \)) will have a much higher concentration of hydrogen ions (\( \text{H}^+ \)) compared to a 1 M solution of acetic acid (\( \text{CH}_3\text{COOH} \)). This is because \( \text{HCl} \) is a strong acid, meaning it ionizes almost completely in water to release all its hydrogen ions. In contrast, \( \text{CH}_3\text{COOH} \) is a weak acid and only partially ionizes, releasing significantly fewer hydrogen ions into the solution. This difference in ionization determines their relative strengths.
In simple words: A 1 M solution of \( \text{HCl} \) has more hydrogen ions than a 1 M \( \text{CH}_3\text{COOH} \) solution. This is because \( \text{HCl} \) is a strong acid and fully breaks apart in water, while \( \text{CH}_3\text{COOH} \) is a weak acid and only partly breaks apart.

🎯 Exam Tip: The concentration of \( \text{H}^+ \) ions directly relates to the strength of an acid. Strong acids fully dissociate, while weak acids only partially dissociate.

Class 10 Science Rajasthan Board Chapter 5 Chemistry in Everyday Life Long Answer Type Questions

Question 1. Design an activity to prove that acids show acidic behaviour only when dissolved in water.
Answer: To demonstrate that acids exhibit their acidic properties only when dissolved in water, an experiment can be set up as follows:
**Materials:** A clean test tube, solid sodium chloride (\( \text{NaCl} \)), concentrated sulfuric acid (\( \text{H}_2\text{SO}_4 \)), a cork with a delivery tube, dry blue litmus paper, and wet blue litmus paper.
**Procedure:**
1. Take a clean test tube and add solid \( \text{NaCl} \) into it.
2. Carefully add some concentrated \( \text{H}_2\text{SO}_4 \) to the test tube.
3. Seal the mouth of the test tube with a cork fitted with a delivery tube, ensuring the evolved gas can exit.
4. A reaction will occur, generating hydrogen chloride (\( \text{HCl} \)) gas.

*(Image description: The diagram shows an experimental setup. A test tube contains solid NaCl, to which concentrated H₂SO₄ is added. A delivery tube is fitted through a cork, leading the evolved gas to another test tube. Labels include "Conc. H2SO4", "NaCl", "Test for dry HCl gas", "test tube".)*
5. Bring a piece of dry blue litmus paper near the mouth of the delivery tube. Observe any color change.
6. Now, take a piece of wet blue litmus paper and bring it near the mouth of the delivery tube. Observe its color change.
**Observation & Conclusion:**
When dry blue litmus paper is brought near the \( \text{HCl} \) gas, no color change is observed. This indicates that dry \( \text{HCl} \) gas does not show acidic properties.
However, when wet blue litmus paper is brought near the \( \text{HCl} \) gas, it immediately turns red. This is because the moisture on the litmus paper dissolves the \( \text{HCl} \) gas, forming hydrochloric acid. This acid then dissociates into \( \text{H}^+ \) and \( \text{Cl}^- \) ions, allowing it to exhibit its acidic behavior. Thus, acids show acidic behavior only in the presence of water.
In simple words: To show acids need water to be acidic: Mix salt and strong acid in a tube to make \( \text{HCl} \) gas. Dry litmus paper won't change color. But wet litmus paper will turn red, proving \( \text{HCl} \) is only acidic with water.

🎯 Exam Tip: Clearly distinguish between \( \text{HCl} \) gas (covalent) and hydrochloric acid (\( \text{HCl(aq)} \), ionic). The presence of water is crucial for ionization and acidic properties.

Question 2. What is bleaching powder? How is bleaching powder produced? Give its chemical equation and write its three uses.
Answer: Bleaching powder is chemically known as calcium oxychloride, with the formula \( \text{CaOCl}_2 \). It is an important chemical compound due to its versatile properties.
**Preparation:** Bleaching powder is produced by passing chlorine gas through dry slaked lime, which is calcium hydroxide (\( \text{Ca(OH)}_2 \)). This is a industrial process.
The chemical equation for its preparation is:
\[ \text{Ca(OH)}_2 \text{(dry)} + \text{Cl}_2 \text{(g)} \rightarrow \text{CaOCl}_2 \text{(s)} + \text{H}_2\text{O} \text{(l)} \]
**Uses:** Bleaching powder has several important uses:
1. **Bleaching Agent:** It is widely used in the textile industry to bleach cotton and linen, and in paper factories to bleach wood pulp, giving them a clean, white appearance.
2. **Oxidizing Agent:** Due to its ability to release chlorine and oxygen, it acts as an effective oxidizing agent in many chemical industries, facilitating various chemical reactions.
3. **Disinfectant:** It is used to disinfect drinking water, making it free from germs and safe for consumption by killing harmful microorganisms.
In simple words: Bleaching powder is \( \text{CaOCl}_2 \). We make it by bubbling chlorine gas through dry slaked lime. Its uses are: 1. To bleach clothes and paper. 2. As a helper chemical in factories. 3. To clean drinking water and kill germs.

🎯 Exam Tip: Remember both the chemical formula and the three main applications of bleaching powder, connecting them to its property as an oxidizing and disinfecting agent.

Question 3. What is baking soda and baking powder chemically? What would happen if we add baking soda in making cakes instead of baking powder?
Answer: Chemically, baking soda is sodium hydrogen carbonate (\( \text{NaHCO}_3 \)). Baking powder, on the other hand, is a mixture of baking soda and a mild edible acid, such as tartaric acid. This combination is essential for its function.
If only baking soda is used in making cakes instead of baking powder, when heated, the baking soda will decompose to produce sodium carbonate. Sodium carbonate has a bitter taste, which would make the cake unpalatable. Baking powder includes tartaric acid specifically to react with the sodium carbonate formed during baking, neutralizing its bitterness and improving the flavor and texture of the cake. This ensures the cake tastes good and is airy.
In simple words: Baking soda is sodium hydrogen carbonate. Baking powder is baking soda mixed with an acid like tartaric acid. If you only use baking soda in a cake, heating it will make a bitter-tasting chemical. The tartaric acid in baking powder stops this bitter taste from happening.

🎯 Exam Tip: Highlight the key difference between baking soda and baking powder (presence of an acid in baking powder) and explain the consequence (bitterness) if only baking soda is used.

Question 4. Write the chemical formula for washing soda. How may it be obtained from baking soda? Name an industrial use of washing soda other than washing clothes.
Answer: The chemical formula for washing soda is \( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \), also known as sodium carbonate decahydrate. It can be prepared by heating baking soda (sodium hydrogen carbonate) to produce sodium carbonate, which is then recrystallized by adding water. This process helps create a stable crystalline form of the compound.
The chemical reactions involved are:
\( 2\text{NaHCO}_3 \xrightarrow{\text{heat}} \text{Na}_2\text{CO}_3 + \text{CO}_2 + \text{H}_2\text{O} \)
\( \text{Na}_2\text{CO}_3 + 10\text{H}_2\text{O} \rightarrow \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \)
Besides washing clothes, washing soda is widely used in the manufacture of glass and paper.
In simple words: Washing soda is \( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \). You make it by heating baking soda, then adding water. It is also used to make glass and paper.

🎯 Exam Tip: Remember the specific chemical names and formulas for baking soda and washing soda, as well as the conditions (like heating) for their conversion.

Question 5.
(a) Why does an aqueous solution of an acid conduct electricity?
(b) How does the concentration of hydronium ions (\( \text{H}_3\text{O}^+ \)) change when a solution of an acid is diluted?
(c) Which has higher pH value, a concentrated or dilute solution of hydrochloric acid?
(d) What do you observe on adding dilute hydrochloric acid to
(i) Sodium carbonate placed in test tube.
(ii) Zinc metal in a test tube?
Answer:
(a) An aqueous solution of an acid conducts electricity because the acid releases ions when dissolved in water. These free ions can move and carry electric charge, allowing the solution to conduct electricity. The presence of mobile charge carriers is essential for electrical conductivity.
(b) When an acid solution is diluted with water, the concentration of hydronium ions (\( \text{H}_3\text{O}^+ \)) decreases per unit volume. This happens because the same number of ions are spread out in a larger volume of solvent.
(c) A dilute solution of hydrochloric acid will have a higher pH value compared to a concentrated solution. This is because dilution reduces the \( \text{H}^+ \) ion concentration, leading to a less acidic solution and thus a higher pH.
(d)
(i) When dilute hydrochloric acid is added to sodium carbonate in a test tube, you will observe effervescence, which means gas bubbles are produced. This gas is carbon dioxide.
The reaction is: \( \text{Na}_2\text{CO}_3 + 2\text{HCl(dil.)} \rightarrow 2\text{NaCl} + \text{CO}_2 + \text{H}_2\text{O} \)
(ii) When dilute hydrochloric acid is added to zinc metal in a test tube, an odourless and colourless hydrogen gas is evolved, which can be seen as bubbles on the surface of the zinc metal. This is a common reaction between active metals and acids.
The reaction is: \( \text{Zn(s)} + 2\text{HCl(dil.)} \rightarrow \text{ZnCl}_2 + \text{H}_2\text{(g)} \)
In simple words:
(a) Acids in water make ions, which carry electricity.
(b) Adding water to acid spreads out the hydronium ions, so there are fewer in the same space.
(c) A weaker acid solution (dilute) has a higher pH.
(d) (i) Adding acid to sodium carbonate makes bubbly carbon dioxide gas.
(ii) Adding acid to zinc metal makes hydrogen gas bubbles.

🎯 Exam Tip: For chemical reactions, always remember the specific observations (like effervescence or gas evolution) and the correct balanced chemical equations. Understanding the underlying principles of ionisation for conductivity is also crucial.