Question 1

A salt, designated as 'X', has seven molecules of water of crystallisation in its formula unit. Identify 'X' from the following options.

Accepted Answer

Answer: FeSO₄. Iron(II) sulphate crystals (FeSO₄·7H₂O), also known as green vitriol, contain exactly seven molecules of water of crystallisation.

Question 2

What is a common characteristic among the crystals of washing soda, copper sulphate, gypsum, and ferrous sulphate?

Accepted Answer

Answer: have a fixed number of water molecules of crystallisation. All these substances are hydrated salts, meaning their crystals contain a definite number of water molecules, known as water of crystallisation.

Question 3

Identify which of the following sets of compounds represents a family of salts.

Accepted Answer

Answer: K₂SO₄, Na₂SO₄, CaSO₄. A family of salts shares a common cation or anion. All salts in option (b) contain the sulphate (SO₄²⁻) anion, making them a family of sulphate salts.

Question 4

Chlorine gas, which is produced from the electrolysis of an aqueous solution of sodium chloride (brine), is utilized in the production of which of the following substances?

Accepted Answer

Answer: Disinfectants. Chlorine gas obtained from the electrolysis of brine is a key component in manufacturing bleaching powder, which is widely used as a disinfectant.

Question 5

A product 'X' is formed when a mixture of baking soda and tartaric acid is heated or dissolved in water. This product 'X' makes bread and cakes soft and spongy. Identify 'X'.

Accepted Answer

Answer: Carbon dioxide. The reaction between baking soda (a base) and tartaric acid (an acid) releases carbon dioxide gas, which causes the dough to rise, making baked goods soft and spongy.

Question 6

What is the chemical formula for washing soda?

Accepted Answer

Answer: Na₂CO₃·10H₂O. Washing soda is chemically known as sodium carbonate decahydrate, and its formula is Na₂CO₃·10H₂O, indicating ten molecules of water of crystallisation.

Question 7

What is the nature of an aqueous solution of potassium nitrate?

Accepted Answer

Answer: Neutral. Potassium nitrate is a salt formed from a strong acid (nitric acid, HNO₃) and a strong base (potassium hydroxide, KOH). Salts of strong acids and strong bases are neutral in nature, resulting in a pH of 7.

Question 8

In which of the following substances is water of crystallization present?
(i) Bleaching Powder
(ii) Plaster of Paris
(iii) Washing Soda
(iv) Baking Soda

Accepted Answer

Answer: (b) (ii) and (iii). Plaster of Paris (CaSO₄·½H₂O) and washing soda (Na₂CO₃·10H₂O) are hydrated salts, meaning they contain fixed water molecules in their crystal structure, known as water of crystallization. Bleaching powder and baking soda do not.

Question 9

Which of the following chemical compounds is utilized in the manufacturing of glass, soap, and paper?

Accepted Answer

Answer: Washing Soda. Washing soda (sodium carbonate, Na₂CO₃) is used extensively in the glass, soap, and paper industries. It acts as a flux in glass making and as a cleaning agent in soap and paper production.

Question 10

What is the pH of an aqueous solution of sodium chloride prepared in distilled water?

Accepted Answer

Answer: 7. Sodium chloride (NaCl) is a salt formed from a strong acid (HCl) and a strong base (NaOH). Therefore, its aqueous solution is neutral with a pH of 7.

Question 11

Among the following compounds (FeSO₄, CuSO₄, CaSO₄, Na₂CO₃), which one possesses the highest number of water molecules of crystallization per formula unit in its stable crystalline state?

Accepted Answer

Answer: Na₂CO₃. In their common hydrated forms, Sodium Carbonate (Washing Soda, Na₂CO₃·10H₂O) has 10 water molecules, which is more than Ferrous Sulphate (FeSO₄·7H₂O), Copper Sulphate (CuSO₄·5H₂O), or Calcium Sulphate (Gypsum, CaSO₄·2H₂O).

Question 12

What is the chemical name of the salt that constitutes tooth enamel?

Accepted Answer

Answer: Calcium phosphate. Tooth enamel, the hardest substance in the human body, is primarily composed of a crystalline form of calcium phosphate known as hydroxyapatite.

Question 13

An aqueous solution of a salt changes the color of blue litmus paper to red. Identify the acid-base reaction that could produce this salt.

Accepted Answer

Answer: HCl and NH₄OH. A solution that turns blue litmus red is acidic. An acidic salt is formed from the reaction of a strong acid (like HCl) and a weak base (like NH₄OH).

Question 14

Which of the following salts is used to remove the permanent hardness of water?

Accepted Answer

Answer: Sodium carbonate decahydrate (Na₂CO₃.10H₂O). Sodium carbonate decahydrate, also known as washing soda, reacts with the soluble magnesium and calcium salts that cause permanent hardness, forming insoluble carbonates that can be filtered out.

Question 15

From the options provided, identify the chemical formula for washing soda.

Accepted Answer

Answer: Na₂CO₃.10H₂O. Washing soda is the common name for sodium carbonate decahydrate, which has the chemical formula Na₂CO₃.10H₂O. The other options represent sodium bicarbonate, sodium carbonate pentahydrate, and sodium hydroxide.

Class 10 Science: More About Salts — Practice Questions with Answers

More Class 10 Science practice