Class 10 Science Chapter 2: Acids, Bases and Salts worksheet with answer key

Answer: (a) Supporting fractured bones in the right position

Bleaching powder bleaches cotton and linen, disinfects drinking water and serves as an oxidising agent. Supporting fractured bones is a use of Plaster of Paris.

Answer: (c) purple

Litmus solution is purple when the solution is neither acidic nor basic; red and blue are its colours in acid and in base.

Answer: (b) calcium carbonate

Carbon dioxide reacts with calcium hydroxide to form calcium carbonate, which is insoluble and makes the lime water milky. Calcium hydrogencarbonate is soluble.

Answer: (d) It is acid rain, and its flow into rivers lowers the pH of the river water.

Rain water with a pH below 5.6 is acid rain. Flowing into rivers it lowers their pH and makes survival of aquatic life difficult, which rules out option (b).

Answer: (c) Methyl orange

Methyl orange is made synthetically. Turmeric, red cabbage extract and litmus are obtained from natural sources.

The bee sting injects an acid, which causes pain and irritation. Baking soda is a mild base; it neutralises the acid, so the pain and irritation lessen.

• the sting injects an acid (1)
• baking soda is a mild base that neutralises the acid (1)

Plants need a specific pH range for healthy growth, so soil that is too acidic must be corrected. Adding a base neutralises the excess acid; quick lime (calcium oxide), slaked lime (calcium hydroxide) or chalk (calcium carbonate) can be used.

• plants grow well only within a specific pH range (1)
• names any two of quick lime, slaked lime, chalk (1)

Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. In Na₂CO₃·10H₂O this water is chemically combined within the crystal, not held as free liquid on its surface, so the crystals are dry to the touch.

• defines water of crystallisation as a fixed number of water molecules in one formula unit of a salt (1)
• the water is chemically combined in the crystal, not free liquid, so the crystals are dry (1)

(a) The stomach produces hydrochloric acid, which helps in the digestion of food. (b) During indigestion the stomach produces too much acid; an antacid is a mild base that neutralises the excess acid. Example: milk of magnesia, Mg(OH)₂, or baking soda. (c) The human body works within a narrow pH range of 7.0 to 7.8, and living organisms survive only within a narrow range of pH change.

• hydrochloric acid, helps digest food (1)
• antacid is a base that neutralises excess acid, with one example (1)
• body works within pH 7.0 to 7.8; organisms survive only in a narrow range (1)

(a) Zn + 2NaOH → Na₂ZnO₂ + H₂; the salt is sodium zincate, and hydrogen gas is released. (b) An oxide that reacts with both acids and bases to give salt and water is an amphoteric oxide. ZnO + 2HCl → ZnCl₂ + H₂O.

• balanced equation and names sodium zincate (1)
• amphoteric oxide (1)
• ZnO + 2HCl → ZnCl₂ + H₂O (1)

(a) Potassium sulphate: from sulphuric acid and potassium hydroxide, a strong acid and a strong base, so neutral. (b) Sodium acetate: from acetic acid, a weak acid (it gives far fewer hydrogen ions than hydrochloric acid of the same concentration), and sodium hydroxide, a strong base, so basic. (c) Sodium hydrogencarbonate: from carbonic acid, a weak acid, and sodium hydroxide, a strong base, so basic; it is a mild basic salt.

• potassium sulphate: H₂SO₄ and KOH, neutral (1)
• sodium acetate: CH₃COOH (weak acid) and NaOH (strong base), basic (1)
• sodium hydrogencarbonate: H₂CO₃ and NaOH, basic (1)