CBSE Class 10 Science Acids bases and salts Sure Shot Questions Set 01

ACIDS, BASES AND SALTS

Question. Alkali is a base that is :
(A) soluble in alcohol.
(B) insoluble in alcohol.
(C) soluble in water.
(D) insoluble in water.
Answer : C

Question. When CO₂ is passed through lime water, it turns milky. The milkiness is due to the formation of -
(A) CaCO₃
(B) Ca(OH)₂
(C) H₂O
(D) CO₂
Answer : A

Question. 10 mL of 0.1 N HCl is added to 990 mL solution of NaCl. The pH of the resulting solution is-
(A) zero
(B) 3
(C) 7
(D) 10
Answer : B

Question. The pH of 0.1M solution of the following increases in the order of :
(A) NaCl < NH4Cl < NaCN < HCl
(B) HCl < NH4Cl < NaCl < NaCN
(C) NaCN < NH4Cl < NaCl < HCl
(D) HCl < NaCl < NaCN < NH4Cl
Answer : B

Question. Behaviour of hydrogen gas towards litmus paper is -
(A) neutral behaviour
(B) turns red litmus to blue
(C) turns blue litmus to red
(D) litmus paper starts burning
Answer : A

Question. Metal carbonates and hydrogen carbonates react with acids to give -
(A) Carbon dioxide gas
(B) Hydrogen gas
(C) Sulphur dioxide gas
(D) Carbon monoxide gas.
Answer : A

Question. Most of the metals combine with dilute acids -
(A) To produce carbon di oxide gas
(B) To form a base.
(C) To liberate hydrogen gas by displacing hydrogen from the acids
(D) To form acidic salt.
Answer : C

Question. Universal indicator is -
(A) the indicator that changes its colours at different iodide ion concentration.
(B) the indicator that shows different colours at different hydrogen ion concentrations.
(C) is effective only at low hydrogen ion concentration.
(D) gives same colour at different pH.
Answer : B

Question. Fresh milk has a pH of 6. On changing into curd, its pH becomes -
(A) more than 6.
(B) less than 6.
(C) remains 6.
(D) 7.
Answer : B

Question. Which of the following aqueous solutions will have highest pH ?
(A) Sodium acetate
(B) Sodium chloride
(C) Ammonium phosphate
(D) Calcium chloride
Answer : A

Question. The pH of a compound is found to be 9. The compound can be -
(A) HCl.
(B) NaOH.
(C) Na₂CO_3.
(D) CH₃COOH.
Answer : C

Question. pH of pure water is -
(A) 0
(B) 1
(C) 7
(D) 14
Answer : C

Question. If pH of solution is 13, means that it is -
(A) weakly acidic
(B) weakly basic
(C) strongly acidic
(D) strongly basic
Answer : D

Question. Which is an acidic indicator ?
(A) phenolphthalein
(B) methylorange
(C) (A) & (B) both
(D) none of these
Answer : A

Question. The chemical formula of 'Rock salt' is -
(A) Na₂CO₃
(B) NaCl
(C) NaHCO₃
(D) KCl
Answer : B

Question. Which of the following has the highest pH ?
(A) Distilled water
(B) 1 M NH₃
(C) 1 M NaOH
(D) Water saturated with chlorine
Answer : C

Question. [OH–] in a solution is 1 mol L–1. The pH of the solution is -
(A) 1
(B) 0
(C) 14
(D) 10–14
Answer : C

Question. pH of an aqueous solution is 5.5. The hydroxyl ion conc. in the solution would be -
(A) –5.5 M
(B) – 8.5 M
(C) 10–8.5 M
(D) 108.5 M
Answer : C

Question. Two solutions A and B have pH Value 2 and 5 respectively their natue will be:
(A) A and B both acidic
(B) A alkaline, B acidic
(C) B alkaline, A acidic
(D) A and B both alkaline
Answer : A

Question. Which of the following salts does not contain water of crystallization?
(a) Blue vitriol
(b) Baking soda
(c) Washing soda
(d) Gypsum
Answer : B

Question. What happens when a solution of an acid is mixed with a solution of a base in a test tube?
(i) The temperature of the solution increases
(ii) The temperature of the solution decreases
(iii) The temperature of the solution remains the same
(iv) Salt formation takes place
(a) (i) only
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (i) and (iv)
Answer : D

Question. Which one of the folIowing reaction is not possible: 
(A) Ca + HVSO₄ → CaSO₄ + H₂
(B) Cu + H₂SO₄ →CuSO₄ + H₂
(C) Zn + H₂SO₄ → ZnSO₄ + H₂
(D) Mg+ H₂SO₄ → MgSO₄ + H₂
Answer : B

Question. Which of the following is not a property of an acid ?
(A) Acids are sour in taste.
(B) Acids turn blue litmus red.
(C) Acids don't react with active metals to give hydrogen.
(D) Acids show neutralization reaction with bases.
Answer : C

VERY SHORT ANSWER TYPE QUESTIONS

1. Name two natural indicators. [1 Mark]

Answer:
1. Litmus.
2. Turmeric.

Teacher's Note:
a) Natural indicators are obtained from natural sources like plants.
b) Litmus is extracted from lichens, and turmeric gives a red colour in basic medium.

2. Name two indicators that are usually used in chemical laboratories to indicate acidic/basic nature of a solution. [1 Mark]

Answer:
1. Methyl orange.
2. Phenolphthalein.

Teacher's Note:
a) These are synthetic indicators commonly used in acid-base titrations in the laboratory.
b) Phenolphthalein is colourless in acidic medium and pink in basic medium.

3. What is the general name of bases that are soluble in water? [1 Mark]

Answer:
1. Alkalis.

Teacher's Note:
a) All alkalis are bases, but all bases are not alkalis.
b) Sodium hydroxide and potassium hydroxide are examples of water-soluble bases (alkalis).

4. What is an acid? [1 Mark]

Answer:
1. An acid is a substance which releases hydrogen ions (H⁺) when dissolved in water.

Teacher's Note:
a) Acids have a sour taste and turn blue litmus red.
b) They react with metals to evolve hydrogen gas.

5. Define base [1 Mark]

Answer:
1. A base is a substance that reacts with an acid to form salt and water, typically releasing hydroxide ions (OH^-) in aqueous solution.

Teacher's Note:
a) Bases are usually metal oxides or metal hydroxides.
b) They have a bitter taste and turn red litmus blue.

6. What is the action of an acid on blue litmus paper? [1 Mark]

Answer:
1. An acid turns blue litmus paper red.

Teacher's Note:
a) This is a standard characteristic test used to identify acidic substances.
b) The colour change is due to the presence of hydrogen ions in the solution.

7. Name two natural substances that contain acid. [1 Mark]

Answer:
1. Lemon (contains citric acid).
2. Tamarind (contains tartaric acid).

Teacher's Note:
a) Organic acids occur naturally in plant and animal sources.
b) Vinegar and tomato are other examples containing acetic acid and oxalic acid respectively.

8. What is the oxide of a metal called? [1 Mark]

Answer:
1. Basic oxide.

Teacher's Note:
a) Metal oxides react with water to form bases or alkalis.
b) Some metal oxides like amphoteric oxides show both acidic and basic behavior.

9. Are all bases alkalis? [1 Mark]

Answer:
1. No, all bases are not alkalis.

Teacher's Note:
a) Only bases that are soluble in water are called alkalis.
b) For example, copper oxide is a base because it reacts with acids, but it is insoluble in water, so it is not an alkali.

10. Which type of substance is used to indicate an acid or a base? [1 Mark]

Answer:
1. Indicators.

Teacher's Note:
a) Indicators change their colour or odour in acidic and basic media.
b) Examples include litmus, methyl orange, and olfactory indicators like vanilla extract.

11. What is the common element present in all acids? [1 Mark]

Answer:
1. Hydrogen.

Teacher's Note:
a) All acids contain hydrogen, which dissociates as hydrogen ions (H⁺) in water.
b) Not all hydrogen-containing compounds are acids (e.g., glucose, alcohol).

12. Give the name and formula of two mineral acids. [1 Mark]

Answer:
1. Hydrochloric acid (HCl).
2. Sulphuric acid (H₂SO₄).

Teacher's Note:
a) Mineral acids are also known as inorganic acids derived from minerals.
b) Nitric acid (HNO₃) is another common mineral acid.

13. Common salt contains a substance which is hygroscopic. Name the substance and write its formula. [1 Mark]

Answer:
1. Magnesium chloride (MgCl₂).

Teacher's Note:
a) Crude common salt contains deliquescent/hygroscopic impurities like magnesium chloride.
b) Due to this impurity, common salt absorbs moisture from the air during the rainy season.

14. Name any two organic acids. [1 Mark]

Answer:
1. Acetic acid (CH₃COOH).
2. Citric acid (C₆H₈O₇).

Teacher's Note:
a) Organic acids are naturally occurring acids derived from plants and animals.
b) They are generally weak acids compared to mineral acids.

15. What is the common to all bases? [1 Mark]

Answer:
1. They produce hydroxide ions (OH^-) when dissolved in water.

Teacher's Note:
a) The basic property of a substance is due to the presence of hydroxide ions.
b) All bases neutralize acids to form salt and water.

16. Name two sources of common salt. [1 Mark]

Answer:
1. Sea water.
2. Rock salt deposits.

Teacher's Note:
a) Sea water is the major source of sodium chloride, obtained by evaporation.
b) Underground rock salt deposits are mined similarly to coal.

17. How do metals react with acid? [1 Mark]

Answer:
1. Metals react with dilute acids to form a salt and evolve hydrogen gas.

Teacher's Note:
a) Equation: Metal + Dilute Acid → Salt + Hydrogen gas.
b) Only reactive metals placed above hydrogen in the reactivity series displace hydrogen from acids.

18. Name two metals that react with a base to produce hydrogen gas. [1 Mark]

Answer:
1. Zinc (Zn).
2. Aluminium (Al).

Teacher's Note:
a) These are amphoteric metals that react with strong bases like sodium hydroxide.
b) The reaction produces a soluble salt and evolves hydrogen gas.

19. Which gas is evolved when sodium carbonate reacts with hydrochloric acid? [1 Mark]

Answer:
1. Carbon dioxide gas (CO₂).

Teacher's Note:
a) Metal carbonates react with acids to liberate carbon dioxide gas with brisk effervescence.
b) Equation: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂.

20. What happens when carbon dioxide gas is passed into lime water? [1 Mark]

Answer:
1. Lime water turns milky due to the formation of insoluble calcium carbonate.

Teacher's Note:
a) On passing excess carbon dioxide, the milkiness disappears due to the formation of soluble calcium hydrogen carbonate.
b) This is a standard test for carbon dioxide gas.

21. Name a sodium compound which loses its water of crystallization on exposure to air. [1 Mark]

Answer:
1. Washing soda crystals (Sodium carbonate decahydrate, Na₂CO₃·10H₂O).

Teacher's Note:
a) This property of losing water of crystallization on exposure to air is called efflorescence.
b) It changes into a monohydrate form upon losing water molecules.

22. A compound of metal is obtained mainly from sea water. Write the name and formula of the compound. [1 Mark]

Answer:
1. Sodium chloride (NaCl).

Teacher's Note:
a) Sodium chloride is commonly known as common salt.
b) It is separated from sea water by the process of solar evaporation.

23. What is the common name and formula of sodium hydroxide? [1 Mark]

Answer:
1. Common name: Caustic soda.
2. Formula: NaOH.

Teacher's Note:
a) It is manufactured by the chlor-alkali process using brine solution.
b) It is a strong alkali used in soap and detergent manufacturing.

24. What is the reaction called in which an acid and a base nullify the effect of each other? [1 Mark]

Answer:
1. Neutralisation reaction.

Teacher's Note:
a) Acid + Base → Salt + Water.
b) In this reaction, hydrogen ions and hydroxide ions combine to form water molecules.

25. Name the salt which was an important symbol in India’s struggle for freedom? [1 Mark]

Answer:
1. Sodium chloride (Common salt / NaCl).

Teacher's Note:
a) Mahatma Gandhi led the Dandi March against the salt tax imposed by the British government.
b) Common salt became a unifying symbol for the entire nation during the independence movement.

26. Name a sodium compound used as a cleansing agent for domestic purposes. [1 Mark]

Answer:
1. Sodium carbonate (Washing soda, Na₂CO₃·10H₂O).

Teacher's Note:
a) It is used for softening hard water and in glass, soap, and paper industries.
b) Sodium hydrogen carbonate (Baking soda) is another sodium compound used in households for cooking.

27. Why does and aqueous solution of an acid conduct electricity? [1 Mark]

Answer:
1. Due to the presence of free mobile ions (H⁺ and anions) in the aqueous solution.

Teacher's Note:
a) Acids dissociate in water to produce ions, which carry electric current.
b) Solutions of compounds like glucose or alcohol do not conduct electricity because they do not form ions in water.

51. Write the chemical formula of quicklime. [1 Mark]

Answer:
1. CaO (calcium oxide).

Teacher's Note:
a) Learn the formula together with the common name.

52. Name a compound of calcium which is used for whitewashing. [1 Mark]

Answer:
1. Calcium hydroxide, Ca(OH)₂, also called slaked lime.

Teacher's Note:
a) Learn the formula together with the common name.

53. Which compound of calcium is used for making cement and glass? [1 Mark]

Answer:
1. Calcium carbonate (limestone), CaCO₃.

Teacher's Note:
a) Learn the formula together with the common name.

54. Write an equation to show the reaction between quicklime and water. [1 Mark]

Answer:
1. CaO + H₂O → Ca(OH)₂ + heat

Teacher's Note:
a) Learn the formula together with the common name.

55. Which compound of calcium is used to produce limelight? [1 Mark]

Answer:
1. Quicklime, calcium oxide (CaO), which glows brightly when heated.

Teacher's Note:
a) Learn the formula together with the common name.

56. Write the chemical name and formula of baking soda. [1 Mark]

Answer:
1. Sodium hydrogen carbonate (sodium bicarbonate), NaHCO₃.

Teacher's Note:
a) Learn the formula together with the common name.

57. Name a compound of sodium which is used in fire extinguisher. [1 Mark]

Answer:
1. Sodium hydrogen carbonate (NaHCO₃), used with an acid in soda-acid fire extinguishers.

Teacher's Note:
a) Learn the formula together with the common name.

58. Write the chemical name and formula of bleaching powder. [1 Mark]

Answer:
1. Calcium oxychloride, CaOCl₂.

Teacher's Note:
a) Learn the formula together with the common name.

59. Two solutions have pH number 4 and 9 respectively which solution has more H+ ion concentration? [1 Mark]

Answer:
1. The solution with pH number 4 has more H+ ion concentration.
2. Lower pH indicates higher concentration of hydrogen ions.

Teacher's Note:
a) pH is inversely proportional to hydrogen ion concentration.
b) Acids have pH less than 7.

60. Which compound of calcium is used for disinfecting water? [1 Mark]

Answer:
1. Bleaching powder, chemically known as calcium oxychloride (CaOCl₂).

Teacher's Note:
a) Chlorine gas is released which kills germs.
b) It is prepared by the action of chlorine on dry slaked lime.

61. Why should cured and sour substances not be kept in brass and copper vessel? [1 Mark]

Answer:
1. Curd and sour substances contain acids.
2. These acids react with the metal vessels to form soluble salts, making the food toxic.

Teacher's Note:
a) Metals react with acids to evolve hydrogen gas and form salts.
b) Copper poisoning can occur if acidic food is stored in copper utensils.

62. Name a compound of calcium which hardens on being mixed with water. [1 Mark]

Answer:
1. Plaster of Paris (Calcium sulphate hemihydrate).

Teacher's Note:
a) It forms gypsum on reacting with water.
b) Chemical formula is CaSO₄. 1/2 H₂O.

63. Write down the molecular formula for one strong and one weak acid. [1 Mark]

Answer:
1. Strong acid: Hydrochloric acid (HCl)
2. Weak acid: Acetic acid (CH₃COOH)

Teacher's Note:
a) Strong acids dissociate completely in water.
b) Weak acids dissociate only partially in aqueous solution.

64. Explain why plaster of Paris should be stored in a moisture proof container? [1 Mark]

Answer:
1. Plaster of Paris absorbs moisture to form a hard solid mass called gypsum.
2. This makes it useless for further applications.

Teacher's Note:
a) The setting process is a hydration reaction.
b) Proper sealing prevents premature setting.

65. Name the gas evolved when dil. sulphuric acid acts on sodium carbonate. [1 Mark]

Answer:
1. Carbon dioxide (CO₂) gas is evolved.

Teacher's Note:
a) Metal carbonates react with dilute acids to form salt, water, and carbon dioxide.
b) CO₂ turns lime water milky.

66. What is the use of common salt in soap industry? [1 Mark]

Answer:
1. Common salt is used for the precipitation (salting out) of soap from the aqueous solution.

Teacher's Note:
a) Addition of sodium chloride decreases the solubility of soap.
b) This allows the soap to separate as a solid.

67. Which compound of calcium is used in paper and textile industries? [1 Mark]

Answer:
1. Bleaching powder (CaOCl₂) is used for bleaching wood pulp in paper factories and washed clothes in textile industries.

Teacher's Note:
a) It acts as an oxidizing agent.
b) It removes color impurities effectively.

68. What do you observe when a burning candle is brought near the test-tube containing hydrogen gas? [1 Mark]

Answer:
1. Hydrogen gas burns with a pop sound.

Teacher's Note:
a) This is a standard confirmatory test for hydrogen gas.
b) The gas burns rapidly due to its combustible nature.

69. Name the indicator used to measure pH values over the whole range. [1 Mark]

Answer:
1. Universal indicator.

Teacher's Note:
a) It is a mixture of several indicators.
b) It shows different colors at different concentrations of hydrogen ions.

70. A white, solid substance is used to disinfect water, and it makes wool shrink-proof. Name the substance. [1 Mark]

Answer:
1. Bleaching powder (Calcium oxychloride, CaOCl₂).

Teacher's Note:
a) It acts as a disinfectant and bleaching agent.
b) Used extensively in textile treatment.

71. How many water of crystallization an present in copper sulphate crystals? [1 Mark]

Answer:
1. Five molecules of water of crystallization (5H₂O).

Teacher's Note:
a) Formula is CuSO₄.5H₂O.
b) Crystals are blue due to these water molecules.

72. Write the name and formula of a compound which contains ten molecules of water of crystallization? [1 Mark]

Answer:
1. Name: Washing soda (Sodium carbonate decahydrate)
2. Formula: Na₂CO₃.10H₂O

Teacher's Note:
a) It is used in glass, soap, and paper industries.
b) It removes permanent hardness of water.

73. Name a sodium compound which is used in softening hard water. [1 Mark]

Answer:
1. Washing soda (Sodium carbonate, Na₂CO₃).

Teacher's Note:
a) It removes both temporary and permanent hardness.
b) It precipitates insoluble salts from hard water.

74. A white powdery substance smells of chlorine and is used for disinfecting drinking water. What is the name of substance? [1 Mark]

Answer:
1. Bleaching powder.

Teacher's Note:
a) Chemical name is calcium oxychloride.
b) Smell of chlorine is due to continuous release of chlorine gas upon exposure to air.

75. What happen when anhydrous copper sulphate is moistened with water? [1 Mark]

Answer:
1. Anhydrous copper sulphate turns blue upon adding water.
2. Hydrated copper sulphate (CuSO₄.5H₂O) is formed.

Teacher's Note:
a) This is a reversible hydration reaction.
b) Used as a test for the presence of moisture.

76. Name the substance produced by the action of chlorine on dry slaked lime. [1 Mark]

Answer:
1. Bleaching powder (CaOCl₂).

Teacher's Note:
a) Reactants are Ca(OH)₂ and Cl₂.
b) Water is formed as a byproduct.

77. Name the compound of calcium used for bleaching cloth. [1 Mark]

Answer:
1. Bleaching powder (Calcium oxychloride).

Teacher's Note:
a) Chlorine present in it acts as the bleaching agent.
b) Used extensively in textile mills.

78. A compound is used to make casts for statues and for holding broken limbs and joints in place. What is this compound? [1 Mark]

Answer:
1. Plaster of Paris (Calcium sulphate hemihydrate).

Teacher's Note:
a) Sets into a hard mass when mixed with water.
b) Chemical formula is CaSO₄. 1/2 H₂O.

79. Write chemical equation to represent the action of dilute hydrochloric acid on bleaching powder? [1 Mark]

Answer:
1. CaOCl₂ + 2HCl → CaCl₂ + H₂O + Cl₂

Teacher's Note:
a) Calcium chloride and water are formed.
b) Chlorine gas is released during the reaction.

80. Represent the reaction between plaster of paris and water in the form of an equation. [1 Mark]

Answer:
1. CaSO₄. 1/2 H₂O + 1 1/2 H₂O → CaSO₄.2H₂O

Teacher's Note:
a) Plaster of Paris reacts with water to form gypsum.
b) Results in a hard, solid mass.

SHORT ANSWER TYPE QUESTIONS

1. What is an acid? Give some examples of organic and inorganic acids. [2 Marks]

Answer:
1. Acids are substances that release hydrogen ions (H+) in aqueous solution and have a sour taste.
2. Organic acids examples: Acetic acid (CH₃COOH), Citric acid.
3. Inorganic acids examples: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄).

Teacher's Note:
a) Organic acids are naturally occurring and carbon-based.
b) Inorganic acids are derived from minerals and are generally stronger.

2. What is a base? Give examples? [2 Marks]

Answer:
1. Bases are substances that release hydroxide ions (OH-) in aqueous solution, taste bitter, and turn red litmus blue.
2. Examples: Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)₂).

Teacher's Note:
a) Water-soluble bases are called alkalis.
b) They neutralize acids to form salt and water.

3. What is an indicator? Give some examples of indicators? [2 Marks]

Answer:
1. An indicator is a dye that changes color when it is put into an acid or a base.
2. Examples: Litmus, Methyl orange, Phenolphthalein.

Teacher's Note:
a) Indicators help in identifying the chemical nature of solutions.
b) Olfactory indicators change smell instead of color.

4. What is litmus? [1 Mark]

Answer:
1. Litmus is a natural purple dye extracted from lichens, a plant belonging to the division Thallophyta, used as an indicator.

Teacher's Note:
a) It turns red in acidic solutions and blue in basic solutions.
b) It is the most common acid-base indicator.

5. Describe some natural acid-base indicators, other than litmus. [3 Marks]

Answer:
1. Turmeric: It is a yellow powder that turns reddish-brown in basic solutions and remains yellow in acidic or neutral solutions.
2. Red cabbage juice: It is red in acidic solutions, green in basic solutions, and purple in neutral solutions.
3. Hydrangea flowers: These flowers change color depending on the acidity of the soil, turning blue in acidic soil and pink in basic soil.

Teacher's Note:
a) Natural indicators are extracted from plants and change color based on the hydrogen ion concentration.
b) Ensure students do not confuse the color change of turmeric in acids with bases.
c) Mentioning red cabbage or colored petals gives full clarity for full marks.

6. What are olfactory indicators? [2 Marks]

Answer:
1. Olfactory indicators are substances whose odor changes in acidic or basic media.
2. Examples include onion, vanilla extract, and clove oil, which lose their characteristic smell in basic solutions but retain it in acidic solutions.

Teacher's Note:
a) Olfactory relates to the sense of smell.
b) Give at least two clear examples to secure full marks.

7. What do you mean by concentrated and dilute acid solutions? [2 Marks]

Answer:
1. A concentrated acid solution contains a high percentage of the acid with a very small amount of water.
2. A dilute acid solution contains a large amount of water mixed with a relatively small amount of acid.

Teacher's Note:
a) Concentration depends on the solute-to-solvent ratio.
b) Dilution decreases the number of hydronium ions per unit volume.

8. Explain why brass and copper vessels are not used to keep curd and sour substances? [3 Marks]

Answer:
1. Curd and other sour substances contain acids.
2. When these sour substances are kept in brass and copper vessels, the acids react with the metal.
3. This reaction forms toxic metal salts that can cause food poisoning and spoil the food.

Teacher's Note:
a) Copper and brass react with organic acids present in sour foods.
b) Focus heavily on the formation of poisonous metallic compounds as the core reason.

9. Name the gas which is liberated when metals react with an acid. Give an example. How is the presence of the gas tested? [3 Marks]

Answer:
1. Hydrogen gas is liberated when metals react with an acid.
2. Example: Zn + 2HCl → ZnCl₂ + H₂
3. Test: Bring a burning splinter near the gas; it burns with a pop sound.

Teacher's Note:
a) Standard metal-acid reaction producing salt and hydrogen gas.
b) The pop sound test is a classic diagnostic for hydrogen gas.

10. HCl, HNO₃ etc. show acidic behavior in aqueous solutions but aqueous solutions of alcohol and glucose do not behave like acids. Explain why? [3 Marks]

Answer:
1. Acids like HCl and HNO₃ dissociate in water to produce hydrogen ions (H⁺) or hydronium ions (H₃O⁺), which cause acidic behavior.
2. Compounds like alcohol and glucose contain hydrogen, but their hydrogen does not dissociate into ions in water.
3. Since they do not release ions, their aqueous solutions do not conduct electricity or show acidic properties.

Teacher's Note:
a) Presence of hydrogen alone does not make a substance an acid; it must ionize in water.
b) Glucose and alcohol have covalent bonds that do not break apart into ions.

11. What would be the nature of solutions when the following salts are dissolved separately in water?
(i) NaCl
(ii) Na₂CO₃
(iii) CH₃COONa
(iv) CuSO₄
(v) (NH₄)₂SO₄
(vi) Na₂SO₄ [3 Marks]

Answer:
(i) NaCl: Neutral
(ii) Na₂CO₃: Basic
(iii) CH₃COONa: Basic
(iv) CuSO₄: Acidic
(v) (NH₄)₂SO₄: Acidic
(vi) Na₂SO₄: Neutral

Teacher's Note:
a) Salts of strong acid and strong base are neutral.
b) Salts of weak acid and strong base are basic, while salts of strong acid and weak base are acidic.

12. What are the functions of sodium chloride in human body? [2 Marks]

Answer:
1. It is essential for generating nerve impulses and muscle contraction.
2. It is used to produce hydrochloric acid in the stomach, which helps in digestion.

Teacher's Note:
a) Common salt is vital for maintaining fluid balance in the body.
b) Mention physiological roles clearly.

13. Given below are the pH values of four different liquids : 7.0, 14.0, 4.0, 2.0
Which of these could be that of
(i) lemon juice.
(ii) distilled water
(iii) 1 M sodium hydroxide solution
(iv) tomato juice [2 Marks]

Answer:
(i) lemon juice: 2.0
(ii) distilled water: 7.0
(iii) 1 M sodium hydroxide solution: 14.0
(iv) tomato juice: 4.0

Teacher's Note:
a) Lower pH values correspond to stronger acids, and higher values to stronger bases.
b) Neutral solutions have a pH of exactly 7.0.

14. Why does an aqueous solutions of an acid conduct electricity? [2 Marks]

Answer:
1. Acids dissolve in water to form hydronium ions (H₃O⁺) and anions.
2. The presence of these mobile ions in the solution allows electricity to flow through it.

Teacher's Note:
a) Conduction requires mobile charged particles.
b) Acids in dry state do not conduct electricity due to lack of free ions.

15. During the dilution of an acid, it is advised that acid should be added to water, not water to acid. Why? [3 Marks]

Answer:
1. The dilution of a concentrated acid is a highly exothermic process.
2. If water is added to concentrated acid, the heat generated causes the mixture to splash out and cause severe chemical burns.
3. Therefore, acid must always be added slowly to water with constant stirring.

Teacher's Note:
a) Emphasize the heat released during dilution.
b) Mention safety precautions to avoid glass breakage or boiling over.

16. Ac acid solution is diluted with water. How does the concentration of hydrogen ions change? [2 Marks]

Answer:
1. When an acid solution is diluted with water, the total number of hydronium ions per unit volume decreases.
2. Therefore, the concentration of hydrogen ions decreases and the pH increases toward neutral.

Teacher's Note:
a) Dilution increases the volume of the solvent without changing solute moles initially, reducing concentration.
b) Note the spelling error in the original question text ("Ac acid" instead of "Acid").

17. What is the pH of a solution? [2 Marks]

Answer:
1. pH is a scale used for measuring hydrogen ion concentration in a solution.
2. Here 'p' stands for potenz in German, meaning power, and pH represents the negative logarithm of hydrogen ion concentration.

Teacher's Note:
a) The pH scale ranges from 0 to 14.
b) Values below 7 are acidic, 7 is neutral, and above 7 are basic.

18. A metal compound when treated with dilute hydrochloride acid forms calcium chloride and a gas. The gas evolved extinguishers a burning splinter. Write the equation for the reaction that occurs. [3 Marks]

Answer:
1. The metal compound is calcium carbonate, which reacts with dilute hydrochloric acid to form calcium chloride, water, and carbon dioxide gas.
2. The gas that extinguishes a burning splinter is carbon dioxide (CO₂).
3. Equation: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

Teacher's Note:
a) Metal carbonates react with acids to yield salt, water, and carbon dioxide.
b) Note the typo in the original question text ("hydrochloride" instead of "hydrochloric").

19. Why does the colour of dry litmus paper not change in contact with dry HCL gas? [2 Marks]

Answer:
1. Color change of litmus paper requires the presence of hydrogen ions in aqueous form.
2. Dry HCl gas does not dissociate to form hydrogen ions in the absence of moisture, hence it shows no acidic property.

Teacher's Note:
a) Water is necessary for the ionization of acids.
b) Dry HCl cannot produce H₃O⁺ ions.

20. How is the concentration of OH^- ions change when excess of base is dissolved in a a solution of sodium hydroxide? [2 Marks]

Answer:
1. When excess base is dissolved in a sodium hydroxide solution, more hydroxide ions are released into the solution.
2. As a result, the concentration of OH^- ions per unit volume increases.

Teacher's Note:
a) Adding more base increases alkalinity and hydroxide ion density.
b) Note the typo in the original question text ("in a a solution").

21. What will happen if solid sodium hydrogencarbonate or a solution of it is heated? Give the equation of the reaction involved? [2 Marks]

Answer:
1. On heating sodium hydrogencarbonate, sodium carbonate, water and carbon dioxide gas are produced.
2. Chemical equation: 2NaHCO₃ (s) → Na₂CO₃ (s) + H₂O (g) + CO₂ (g)

Teacher's Note:
a) This is a thermal decomposition reaction used in baking.
b) Carbon dioxide gas evolved turns lime water milky.

22. Give two important uses of washing soda. [2 Marks]

Answer:
1. It is used in glass, soap and paper industries.
2. It is used for removing permanent hardness of water.

Teacher's Note:
a) Washing soda is sodium carbonate decahydrate.
b) Mentioning chemical formula Na₂CO₃.10H₂O adds clarity.

23. Give two important uses of baking soda. [2 Marks]

Answer:
1. It is used for making baking powder, which is a mixture of baking soda and a mild edible acid like tartaric acid.
2. It is used in soda-acid fire extinguishers.

Teacher's Note:
a) Baking soda is sodium hydrogencarbonate (NaHCO₃).
b) It acts as an antacid to neutralize stomach acidity.

24. A baker found that the cake prepared by him was hard and small in size. Which ingredient had he forgotten to add that would have made the cake fluffy? Give reasons. [3 Marks]

Answer:
1. The baker had forgotten to add baking powder (or baking soda).
2. Baking powder releases carbon dioxide gas on heating.
3. The trapped carbon dioxide bubbles make the cake rise and become soft and spongy.

Teacher's Note:
a) The reaction produces sodium salt of acid, water and carbon dioxide.
b) Without this gas expansion, the batter remains dense.
c) Mentioning the role of tartaric acid helps complete the explanation.

25. How is soda ash obtained from washing soda crystals? Support your answer by a chemical equation. [2 Marks]

Answer:
1. Soda ash is obtained by heating washing soda crystals (sodium carbonate decahydrate), which loses its water of crystallization.
2. Chemical equation: Na₂CO₃.10H₂O (s) → Na₂CO₃ (s) + 10H₂O (g)

Teacher's Note:
a) Anhydrous sodium carbonate is known as soda ash.
b) Water molecules bound in the crystal lattice are driven off upon heating.

26. How does a fire extinguisher work? [3 Marks]

Answer:
1. A soda-acid fire extinguisher contains sodium hydrogencarbonate and sulfuric acid in separate containers inside.
2. When the knob is pressed, the acid reacts with the sodium hydrogencarbonate to release a large amount of carbon dioxide gas.
3. Carbon dioxide being heavier than air covers the fire like a blanket and cuts off the supply of oxygen, extinguishing the fire.

Teacher's Note:
a) CO₂ does not support combustion.
b) The pressure built up forces the liquid out through the nozzle.
c) It is effective for fires involving inflammable materials and electrical equipment.

27. Why is an aqueous solution sodium carbonate alkaline in nature? [2 Marks]

Answer:
1. Sodium carbonate undergoes salt hydrolysis when dissolved in water.
2. It produces a strong base (sodium hydroxide) and a weak acid (carbonic acid), resulting in an alkaline solution.

Teacher's Note:
a) The presence of excess hydroxide ions turns red litmus blue.
b) The pH of the resulting solution is greater than 7.

28. A given compound of sodium is used to remove hardness of water and also as a reagent in the laboratory. Identify the compound and mention two of its uses. [3 Marks]

Answer:
1. The compound is sodium carbonate decahydrate (washing soda), Na₂CO₃.10H₂O.
2. Use 1: It is used in glass, soap, and paper industries.
3. Use 2: It is used as a cleaning agent for domestic purposes and softening hard water.

Teacher's Note:
a) Sodium carbonate acts as a precipitating agent for hardness ions.
b) Laboratory reagent uses include qualitative and quantitative analysis.
c) Always state the chemical name alongside the common name.

29. How is bleaching powder prepared? Give the reaction. [2 Marks]

Answer:
1. Bleaching powder is prepared by the action of chlorine gas on dry slaked lime.
2. Chemical equation: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Teacher's Note:
a) Chlorine used is a byproduct of the chlor-alkali process.
b) The actual composition of bleaching powder is quite complex.

30. What happens when bleaching powder is left exposed to air? [2 Marks]

Answer:
1. When bleaching powder is left exposed to air, it reacts with carbon dioxide.
2. This reaction releases chlorine gas, which is responsible for the bleaching action.

Teacher's Note:
a) Equation: CaOCl₂ + CO₂ → CaCO₃ + Cl₂.
b) It loses its chlorine smell and potency over time.

31. State three important uses of bleaching powder? [3 Marks]

Answer:
1. For bleaching cotton and linen in the textile industry and wood pulp in paper factories.
2. For disinfecting drinking water to make it free of germs.
3. As an oxidizing agent in many chemical industries.

Teacher's Note:
a) The active ingredient providing bleaching action is chlorine.
b) It ensures safe municipal water supplies.
c) Mentioning the physical state or formula ensures complete credit.

32. (i) Name the chemical used in hospitals for setting fractured bones. [1 Mark]

Answer:
1. Plaster of Paris.

Teacher's Note:
a) It sets into a hard mass on mixing with water.

(ii) State the name of the above chemical and its formula. [2 Marks]

Answer:
1. Chemical name: Calcium sulphate hemihydrate.
2. Chemical formula: CaSO₄.1/2H₂O

Teacher's Note:
a) The term hemihydrate indicates half a molecule of water of crystallization per calcium sulphate molecule.
b) Ensure correct placement of the fraction in the formula.

(iii) How is the above compound prepared? [2 Marks]

Answer:
1. It is prepared by heating gypsum at 373 K.
2. Chemical equation: CaSO₄.2H₂O → CaSO₄.1/2H₂O + 1.1/2H₂O

Teacher's Note:
a) Temperature control is critical to prevent complete dehydration.
b) Overheating converts gypsum to anhydrous calcium sulphate (dead burnt plaster).

33. What is gypsum? What happens when gypsum is heated to 393k? [3 Marks]

Answer:
1. Gypsum is a naturally occurring mineral which is calcium sulphate dihydrate (CaSO₄.2H₂O).
2. When gypsum is heated to 393 K (120 °C), it loses all its water of crystallization.
3. It forms anhydrous calcium sulphate, which loses its setting property and is known as dead burnt plaster.

Teacher's Note:
a) Distinguish clearly between heating at 373 K and 393 K.
b) Anhydrous calcium sulphate cannot rehydrate into plaster of Paris.
c) Write correct chemical formulas for full credit.

34. Explain giving reasons: “Potassium hydrogentartrate is a component of baking powder used in making cakes”. [3 Marks]

Answer:
1. Baking powder contains baking soda and a mild edible acid like potassium hydrogentartrate (or tartaric acid).
2. The acid neutralizes the sodium carbonate produced during the heating of baking soda.
3. If sodium carbonate is not neutralized, the cake will taste bitter due to its basic nature.

Teacher's Note:
a) The acid reacts with sodium hydrogencarbonate to release carbon dioxide gas.
b) Neutralization removes the bitter taste.
c) Essential concept in baking chemistry.

35. A white amorphous powder emits a greenish yellow gas having a smell of chlorine. It is used to remove yellowness of white clothes in laundries. Identify the powder. Write the chemical equation involved in its preparation. [3 Marks]

Answer:
1. The white powder is bleaching powder (Calcium oxychloride, CaOCl₂).
2. Preparation involves passing chlorine gas over dry slaked lime.
3. Chemical equation: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Teacher's Note:
a) Greenish yellow gas with chlorine smell is the key identifier.
b) Bleaching action is due to oxidation by chlorine.
c) Ensure balanced chemical equations are written.

36. You are provided with two solutions A and B having pH 6 and 8 respectively. Which of the solutions does contain more H+ ion concentration? Which of them is acidic and which one basic? [3 Marks]

Answer:
1. Solution A has a pH of 6 and Solution B has a pH of 8.
2. Solution A contains more H⁺ ion concentration because lower pH indicates higher acidity.
3. Solution A is acidic and Solution B is basic.

Teacher's Note:
a) pH is inversely proportional to hydrogen ion concentration.
b) Neutral pH is 7 at standard conditions.
c) Clearly categorize both solutions to avoid losing marks.

37. Do basic solution also have H+ ions. If yes, then why are they basic? [2 Marks]

Answer:
1. Yes, basic solutions also have H⁺ ions.
2. They are basic because the concentration of hydroxide ions (OH^-) is much higher than the concentration of hydrogen ions (H⁺).

Teacher's Note:
a) Water molecules always maintain an ionic product equilibrium.
b) Basic nature is determined by the predominance of OH^- ions.

38. What do the farmers do to treat the soil when it becomes too acidic? [2 Marks]

Answer:
1. Farmers treat acidic soil by adding basic substances such as quicklime (calcium oxide), slaked lime (calcium hydroxide), or chalk (calcium carbonate).
2. These bases neutralize the excess acidity in the soil.

Teacher's Note:
a) Plant growth is stunted in highly acidic or basic soils.
b) Neutralization restores optimal pH for crop growth.

39. What effect does a bee-sting produce on human body? What is its remedy? [2 Marks]

Answer:
1. A bee-sting injects an acidic liquid into the skin, causing pain and irritation.
2. The remedy is to apply a mild base like baking soda to the affected area to neutralize the acid.

Teacher's Note:
a) Bee stings contain methanoic (formic) acid.
b) Mild bases relieve the pain through neutralization.

40. What is the chemical substance injected into a man’s skin when (a) an ant stings him (b) a nettle-leaf stings him? Suggest remedy to get relief from the effects of the stings. [3 Marks]

Answer:
1. (a) Ant sting injects methanoic acid (formic acid).
2. (b) Nettle-leaf sting also injects methanoic acid.
3. Remedy: Rubbing with a mild base like baking soda provides relief by neutralization.

Teacher's Note:
a) Both stings inject organic acids causing a burning sensation.
b) Dock plant leaves, which often grow beside nettles, can also be rubbed as a natural remedy.
c) Always address all parts of the question clearly.

41. How are the lives of aquatic animals affected with change in pH of the river water? [2 Marks]

Answer:
1. Aquatic animals can survive only within a narrow range of pH change.
2. When acid rain lowers the pH of river water below normal, the survival of aquatic life becomes difficult and can lead to their death.

Teacher's Note:
a) Acid rain is primarily caused by sulfur and nitrogen oxides.
b) Changes in pH disrupt biological processes in aquatic organisms.

42. Explain the following: “Distilled water does not conduct electricity, but rain water does”. [2 Marks]

Answer:
1. Distilled water is pure and does not contain any dissolved ionic compounds, so it has no free ions to conduct electricity.
2. Rain water dissolves acidic gases like carbon dioxide and sulfur dioxide from the air, forming ions which allow it to conduct electricity.

Teacher's Note:
a) Electrical conductivity in liquids requires the presence of mobile ions.
b) Pure water is a poor conductor of electricity.

43. Why is an aqueous solution of sodium chloride neutral, whereas that of ammonium chloride acidic? [2 Marks]

Answer:
1. Sodium chloride is a salt of a strong acid (HCl) and a strong base (NaOH), so its aqueous solution is neutral with a pH of 7.
2. Ammonium chloride is a salt of a strong acid (HCl) and a weak base (NH₄OH), so its aqueous solution undergoes hydrolysis to produce an acidic solution with a pH less than 7.

Teacher's Note:
a) Salt hydrolysis determines the acidic or basic nature of salt solutions.
b) Strong acid and strong base salts do not hydrolyze significantly.

44. An efflorescent white, crystalline substance dissolves in water to produce an alkaline solution. The substance is used as a cleansing agent. Identify the substance and mention two uses it. [2 Marks]

Answer:
1. The substance is washing soda, which has the chemical formula Na₂CO₃ · 10H₂O.
2. Two uses of washing soda are in glass, soap, and paper industries, and for removing permanent hardness of water.

Teacher's Note:
a) Washing soda is sodium carbonate decahydrate.
b) Efflorescence is the loss of water of crystallization on exposure to dry air.

45. A white, powdery compound of calcium is used for making toys and casts of statues. It hardens when mixed with water. Identify the compound. Write the chemical equation of its preparation. [3 Marks]

Answer:
1. The compound is Plaster of Paris, chemically known as calcium sulfate hemihydrate (CaSO₄ · \(\frac{1}{2}\)H₂O).
2. It is prepared by heating gypsum (CaSO₄ · 2H₂O) at 373 K.
3. Chemical equation: CaSO₄ · 2H₂O → (Heating at 373 K) → CaSO₄ · \(\frac{1}{2}\)H₂O + 1\(\frac{1}{2}\)H₂O

Teacher's Note:
a) Temperature control during the heating of gypsum is critical to prevent complete dehydration.
b) Plaster of Paris sets into a hard mass due to hydration back into gypsum.
c) Always mention physical states and temperature in chemical equations.

46. What is the chemical formula of plaster of paris? How is it prepared? State the common and the chemical names of the compound formed when plaster of paris mixed with water? [3 Marks]

Answer:
1. The chemical formula of Plaster of Paris is CaSO₄ · \(\frac{1}{2}\)H₂O.
2. It is prepared by heating gypsum at 373 K, causing it to lose water molecules.
3. When mixed with water, the compound formed is Gypsum, with the chemical name Calcium sulfate dihydrate (CaSO₄ · 2H₂O).

Teacher's Note:
a) Ensure the water of crystallization is written correctly as a fraction for the hemihydrate.
b) Do not confuse the starting material with the product formed after adding water.
c) Plaster of Paris hardens quickly when mixed with the right proportion of water.

47. State two uses of the following: [2 Marks]
(i) Sodium hydroxide
(ii) Chlorine
(iii) Hydrogen
(iv) Hydrochloric acid

Answer:
1. (i) Sodium hydroxide: Used in de-greasing metals and making soaps and detergents.
2. (ii) Chlorine: Used in water purification and manufacturing PVC.
3. (iii) Hydrogen: Used in the hydrogenation of oils and production of ammonia.
4. (iv) Hydrochloric acid: Used for cleaning steel and in the production of ammonium chloride.

Teacher's Note:
a) These substances are key products of the chlor-alkali process.
b) Give exact industrial applications for full credit.

48. (a) What is the common name of the compound CaOCl₂.
(b) Name the raw material used for the preparation of plaster of paris.
(c) Which property of plaster of paris is utilized in making casts for broken limbs in hospitals? [3 Marks]

Answer:
1. (a) Bleaching powder.
2. (b) Gypsum.
3. (c) Its property of setting into a hard solid mass when mixed with a proper quantity of water.

Teacher's Note:
a) Answer each sub-part clearly by labeling them as (a), (b), and (c).
b) Bleaching powder is produced by the action of chlorine on dry slaked lime.
c) Gypsum must be heated carefully at 373 K to yield Plaster of Paris.

49. What happens when a cold and concentrate solution of sodium chloride reacts with ammonia and carbon dioxide? Write the chemical equation of the reaction which takes place. [2 Marks]

Answer:
1. A cold and concentrated solution of sodium chloride (brine) reacts with ammonia and carbon dioxide to produce sodium hydrogen carbonate and ammonium chloride.
2. Chemical equation: NaCl + H₂O + CO₂ + NH₃ → NaHCO₃ + NH₄Cl

Teacher's Note:
a) This reaction is the first step in the Solvay process for manufacturing sodium carbonate.
b) Sodium hydrogen carbonate precipitates out because it is sparingly soluble in a cold solution.

50. Write the chemical formula of ammonium chloride. Explain why an aqueous solution of ammonium chloride is acidic in nature? Illustrate your answer with the help of a chemical equation. [3 Marks]

Answer:
1. The chemical formula of ammonium chloride is NH₄Cl.
2. An aqueous solution of ammonium chloride is acidic because it is a salt of a strong acid (HCl) and a weak base (NH₄OH). The ammonium ion undergoes hydrolysis to produce hydrogen ions in water.
3. Chemical equation: NH₄Cl + H₂O ⇌ NH₄OH + H⁺ + Cl^-

Teacher's Note:
a) Emphasize that the strong acid component dominates the pH of the salt solution.
b) Show both the salt dissociation and the hydrogen ion release clearly.
c) The pH of this solution is less than 7.

LONG ANSWER TYPE QUESTIONS

1. What is baking soda? How is it obtained from sodium chjloride? Mention any two uses of baking soda. [4 Marks]

Answer:
1. Baking soda is chemically known as sodium hydrogen carbonate or sodium bicarbonate (NaHCO₃).
2. It is obtained by reacting a cold and concentrated solution of sodium chloride (brine) with ammonia and carbon dioxide.
3. Chemical equation: NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
4. Two uses: It is used for making baking powder (mixture of baking soda and a mild edible acid) and as an ingredient in antacids to neutralize stomach acidity.

Teacher's Note:
a) Note the spelling correction for sodium chloride as printed in the question paper.
b) Explain the thermal decomposition of baking soda when heated during cooking.
c) Mention the role of the mild edible acid in baking powder.
d) Ensure balanced chemical equations are written with correct reactant states.

2. What is the commercial name of bleaching powder? How is bleaching powder prepared? What are its different uses? [4 Marks]

Answer:
1. The commercial name of bleaching powder is bleaching powder, and its chemical name is calcium oxychloride (CaOCl₂).
2. It is prepared by the action of chlorine gas (produced during the chlor-alkali process) on dry slaked lime (Ca(OH)₂).
3. Chemical equation: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
4. Uses: Bleaching cotton and linen in the textile industry, bleaching wood pulp in paper factories, and disinfecting drinking water to make it free of germs.

Teacher's Note:
a) Dry slaked lime must be used instead of wet slaked lime for effective reaction.
b) Chlorine used here is a by-product of the electrolysis of aqueous sodium chloride.
c) State at least three distinct industrial or domestic applications.
d) Highlight the active chemical formula CaOCl₂ although its actual composition is quite complex.

3. What do you mean by the strength of an acid? What are strong and weal acids? [3 Marks]

Answer:
1. The strength of an acid refers to its ability to dissociate into hydrogen ions (H⁺) in an aqueous solution.
2. Strong acids are acids that completely dissociate in water to produce a high concentration of hydrogen ions, such as hydrochloric acid (HCl) and sulfuric acid (H₂SO₄).
3. Weak acids are acids that dissociate only partially in water, producing a low concentration of hydrogen ions, such as acetic acid (CH₃COOH) and carbonic acid (H₂CO₃).

Teacher's Note:
a) Differentiate clearly between concentration of an acid and its strength.
b) Give standard chemical examples for both strong and weak acids.
c) Note the spelling correction for weak acids as printed in the question.

4. What do you mean by the strength of a base? What are strong and weak base? [3 Marks]

Answer:
1. The strength of a base refers to its ability to dissociate into hydroxide ions (OH^-) in an aqueous solution.
2. Strong bases are bases that completely dissociate in water to yield a high concentration of hydroxide ions, such as sodium hydroxide (NaOH) and potassium hydroxide (KOH).
3. Weak bases are bases that dissociate only partially in water, yielding a low concentration of hydroxide ions, such as ammonium hydroxide (NH₄OH) and calcium hydroxide (Ca(OH)₂).

Teacher's Note:
a) Base strength depends on the extent of hydroxide ion production upon dissolution.
b) Alkalis are bases that dissolve in water; all alkalis are bases, but not all bases are alkalis.
c) Provide clear examples for each category to ensure complete marks.

5. Three test tubes A, B and C contain distilled water, a basic solution and an acid solution separately. How would you identify the contents of the test tubes with the help of a red litmus paper only? [3 Marks]

Answer:
1. Put a drop of each solution on red litmus paper.
2. The solution which turns red litmus blue is a basic solution.
3. Take this now blue litmus paper and use it with the remaining two solutions; the one that turns the blue litmus red is the acid solution.
4. The remaining third solution which has no effect on either red or blue litmus is distilled water.

Teacher's Note:
a) Acids turn blue litmus red, and bases turn red litmus blue.
b) Distilled water is neutral, so it shows no colour change on either litmus paper.
c) A sequential testing method is required when only one type of indicator paper is available.

6. What are the different uses of sodium carbonate (Washing soda)? [3 Marks]

Answer:
1. It is used in glass, soap and paper industries.
2. It is used in the manufacture of sodium compounds such as borax.
3. It is used as a cleaning agent for domestic purposes and for removing permanent hardness of water.

Teacher's Note:
a) Sodium carbonate decahydrate is commonly known as washing soda.
b) Hard water contains calcium and magnesium salts which are removed by precipitation with washing soda.
c) Mentioning industrial applications helps secure full marks.

7. State the important properties of washing soda. [2 Marks]

Answer:
1. It is a transparent crystalline solid that is soluble in water.
2. Its aqueous solution is alkaline in nature, which turns red litmus blue.

Teacher's Note:
a) The chemical formula is Na₂CO₃ · 10H₂O.
b) On exposure to dry air, it loses 9 molecules of water of crystallisation to form a monohydrate.

8. What happens when carbon dioxide gas is passed through limewater? Give equations for the reactions that take place. [3 Marks]

Answer:
1. When carbon dioxide gas is passed through limewater, it turns milky due to the formation of insoluble calcium carbonate.
2. Equation: Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O (l)
3. When excess carbon dioxide is passed, the milkiness disappears due to the formation of soluble calcium hydrogen carbonate: CaCO₃ (s) + H₂O (l) + CO₂ (g) → Ca(HCO₃)₂ (aq)

Teacher's Note:
a) Limewater test is a standard laboratory test for identifying carbon dioxide gas.
b) Writing balanced chemical equations with physical states is essential for full marks.
c) The second reaction explains why milkiness disappears on prolonged bubbling of carbon dioxide.

9. With the help of universal indicator the pH values of solutions A, B, C, D and E were found to be 5, 2, 12, 7 and 10 respectively. Say which solution is (i) neutral (ii) strongly base (iii) strongly acidic (iv) weakly acid (v) weakly basic. Arrange the pH in the increasing order of H+ ions configuration. [5 Marks]

Answer:
(i) Neutral solution: D (pH = 7)
(ii) Strongly basic solution: C (pH = 12)
(iii) Strongly acidic solution: B (pH = 2)
(iv) Weakly acidic solution: A (pH = 5)
(v) Weakly basic solution: E (pH = 10)
Increasing order of H+ ion concentration: 12 (C) < 10 (E) < 7 (D) < 5 (A) < 2 (B)

Teacher's Note:
a) pH is inversely proportional to hydrogen ion concentration.
b) A lower pH value denotes higher acidity and higher H+ ion concentration.
c) Neutral pH is exactly 7, values below 7 are acidic, and values above 7 are basic.
d) Care must be taken to reverse the pH order when asked for increasing order of H+ ions.

10. Discuss briefly the reactions occurring when a concentrated solution of sodium chloride (brine) is electrolyzed? [3 Marks]

Answer:
1. When electricity is passed through an aqueous solution of sodium chloride (brine), it decomposes to form sodium hydroxide, chlorine gas, and hydrogen gas.
2. Equation: 2NaCl (aq) + 2H₂O (l) → 2NaOH (aq) + Cl₂ (g) + H₂ (g)
3. Chlorine gas is given off at the anode, hydrogen gas is released at the cathode, and sodium hydroxide solution is formed near the cathode.

Teacher's Note:
a) This process is known as the chlor-alkali process because of the products formed (chlor for chlorine and alkali for sodium hydroxide).
b) Remembering electrode locations is crucial: chlorine at anode, hydrogen at cathode.
c) Brine is defined as a concentrated aqueous solution of sodium chloride.

11. Explain how is washing soda produced using sodium chloride as one of the raw materials? [3 Marks]

Answer:
1. Sodium chloride is reacted with ammonia, carbon dioxide, and water to produce sodium hydrogen carbonate and ammonium chloride.
2. Sodium hydrogen carbonate is heated to give sodium carbonate, water, and carbon dioxide.
3. Recrystallization of sodium carbonate gives washing soda: Na₂CO₃ + 10H₂O → Na₂CO₃ · 10H₂O

Teacher's Note:
a) This sequence is part of the industrial Solvay process.
b) All intermediate steps and balanced equations should be stated clearly.
c) Washing soda is chemically sodium carbonate decahydrate.

12. (a) What is a salt? Give the names and formula of any two salts. Also name the acids and bases from which these salts may be obtained.
(b) What is meant by hydrated and anhydrous salts? Explain with example. [5 Marks]

Answer:
(a) A salt is an ionic compound formed by the neutralisation reaction between an acid and a base. Example 1: Sodium chloride (NaCl), obtained from hydrochloric acid (HCl) and sodium hydroxide (NaOH). Example 2: Potassium sulphate (K₂SO₄), obtained from sulphuric acid (H₂SO₄) and potassium hydroxide (KOH).
(b) Hydrated salts contain a fixed number of water molecules attached to one formula unit of a salt, known as water of crystallisation (e.g., Copper sulphate pentahydrate, CuSO₄ · 5H₂O). Anhydrous salts are those that do not contain any water of crystallisation (e.g., anhydrous copper sulphate, CuSO₄).

Teacher's Note:
a) Salts are composed of positively charged ions (cations) and negatively charged ions (anions).
b) Water of crystallisation gives many crystals their characteristic shape and colour.
c) Heating hydrated copper sulphate drives off water, turning blue crystals white.
d) Ensure both parts (a) and (b) are answered with valid chemical examples.

13. (a) What is plaster of paris? Write its chemical formula.
(b) How is plaster of paris prepared? Write the chemical equation of the reaction involved.
(c) Explain why plaster of paris should be stored in a moisture proof container.
(d) State two important uses of plaster of paris. [4 Marks]

Answer:
(a) Plaster of Paris is a hemihydrate of calcium sulphate, and its chemical formula is CaSO₄ · \(\frac{1}{2}\) H₂O.
(b) It is prepared by heating gypsum (calcium sulphate dihydrate) at 373 K: CaSO₄ · 2H₂O → CaSO₄ · \(\frac{1}{2}\) H₂O + 1\(\frac{1}{2}\) H₂O.
(c) It must be stored in a moisture-proof container because moisture can cause it to absorb water and slowly set into a hard solid mass of gypsum, rendering it useless.
(d) Two uses are: (i) Setting fractured bones in the correct position, and (ii) Making toys, decorative materials, and smooth surfaces.

Teacher's Note:
a) Precise temperature control (373 K) during preparation prevents gypsum from losing all water of crystallisation to form dead burnt plaster.
b) The fractional water molecule in the formula represents one water molecule shared between two formula units of calcium sulphate.
c) The setting reaction is the reverse of preparation, forming a hard mass of gypsum.
d) All four sub-parts carry individual weightage and must be clearly numbered.

14. (a) What is bleaching powder? Write its chemical formula.
(b) How is bleaching powder prepared? Write the chemical equation of the reaction involved.
(c) State two important uses of bleaching powder. [3 Marks]

Answer:
(a) Bleaching powder is calcium oxychloride, and its chemical formula is CaOCl₂.
(b) It is prepared by the action of chlorine gas on dry slaked lime: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O.
(c) Two uses are: (i) For bleaching cotton and linen in the textile industry, and (ii) As a disinfectant for drinking water to make it free of germs.

Teacher's Note:
a) Chlorine used in this process is a by-product of the chlor-alkali process.
b) Although the actual composition of bleaching powder is quite complex, it is represented simply as CaOCl₂.
c) Ensure the balanced chemical equation includes dry slaked lime.

15. (a) What happens when zinc granules are heated with sodium hydroxide solution? Write chemical equation of the reaction which takes place.
(b) What happens when basses react with nonmetals oxides? Explain with the help of an example. What does this reaction tell us about the nature of non-metal oxides? [4 Marks]

Answer:
(a) When zinc granules are heated with sodium hydroxide solution, sodium zincate is formed along with the evolution of hydrogen gas: Zn + 2NaOH → Na₂ZnO₂ + H₂.
(b) When bases react with non-metal oxides, they produce salt and water, which is similar to a neutralisation reaction. Example: Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. This reaction tells us that non-metal oxides are acidic in nature.

Teacher's Note:
a) Reaction of metals with strong bases like sodium hydroxide does not occur with all metals, but active metals like zinc displace hydrogen.
b) The production of salt and water when a base reacts with a non-metal oxide proves that non-metal oxides are acidic.
c) Sodium zincate formula is Na₂ZnO₂.
d) Both parts require correct chemical equations to achieve full credit.

Question. 10^–3 mole of KOH is added to 10 litres of pure water at 25°C. The pH will change by (assume no change in volume occurs)
(A) 3
(B) 4
(C) 7
(D) 11
Answer : A

Question. On reacting a compound of calcium (x) with water compound (y) is obtained. (y) on boiling with NH4Cl a gas (z) is obtained. x, y & z respectively are :
(A) CaCO₃, CaO, NH₃
(B) CaCO₃, CaO, Cl₂
(C) CaO, CaCl₂, Cl₂
(D) CaO, Ca(OH)₂, NH₃
Answer : D

Question. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change?
(a) Baking powder
(b) Lime
(c) Ammonium hydroxide solution
(d) Hydrochloric acid
Answer : D

Question. Plaster of paris hardens by:
(A) Losing CaCI₂
(B) Absorbing CO₂
(C) Absorbing water
(D) Releasing water
Answer : C

Question. Basic radical is: 
(A) Positively Charged ion
(B) Negatively charged ion
(C) Neutral atom
(D) None of the above
Answer : A

Question. During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to
(a) absorb the evolved gas
(b) moisten the gas
(c) absorb moisture from the gas
(d) absorb Cl– ions from the evolved gas
Answer : C
 

ASSERTION REASON TYPE QUESTIONS

For the following question numbers (1-5) two statements are given- one labeled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
a) Both A and R are true, and R is correct explanation of the assertion.
b) Both A and R are true, but R is not the correct explanation of the assertion.
c) A is true, but R is false.
d) A is false, but R is true

Question. Assertion: Plaster of Paris is a is a white powder used to join fractured bones
Reason: On mixing with water plaster of paris changes to Gypsum giving a solid hard mass
Answer: A

Question. Assertion: Our stomach produces Sulphuric acid, which helps in digestion of food.
Reason: During indigestion excess acid secreted is neutralized by using bases called antacids.
Answer: D

Question. Assertion: Sodium Hydroxide is formed during Chlor-alkali process
Reason: Electricity is passed through Sodium Hydroxide during chlor- alkali process.
Answer: C

Question. Assertion: After white washing the walls, a shiny white finish on walls is obtained after two to three days.
Reason: Calcium Oxide reacts with Carbon dioxide to form Calcium Hydrogen Carbonate which gives shiny white finish.
Answer: A

Question. What is acid rain?
Answer: When the pH of the rain water is less than 5.6, it is called acid rain

Question. Write any one use of Chlorine
Answer: In water treatment and making pesticides (any other suitable use)

29. A solution reacts with crushed egg-shells to give a gas that turns lime water milky. Say, whether the solution contains an acid or a base.

30. Which type of medicine is used to treat indigestion?

31. Which compound of a metal is a constituent of many dry soap powders?

32. Name the acid which is used as a bathroom cleaner.

34. Why is a basic substance used to treat a honey-bee sting?

35. A solution turns blue litmus re. What is it pH value?

36. Which one is more acidic, pH = 2 or pH = 5?

37. Which one of the two solutions is more basic, pH = 8 or pH = 11?

39. A milkman adds some baking soda to fresh milk. How will the pH of the fresh milk change?

44. Mention the property of sodium carbonate that makes it useful as an ingredient for dry soap powders.