Acids, Bases And Salts Book Back Questions 9th Science Lesson 14

9th Science Lesson 14

14] Acids, Bases And Salts

Book Back Questions with Answer and Do You Know Box Content

Do You Know?

All acids essentially contain one or more hydrogens. But all the hydrogen containing substances are not acids. For example, methane (CH₄) and ammonia (NH₃) also contain hydrogen. But they do not produce H⁺ ions in aqueous solution.

For acids, we use the term basicity that refers to the number of replaceable hydrogen atoms present in one molecule of an acid. For example, acetic acid (CH₃COOH) has four hydrogen atoms but only one can be replaced. Hence it is monobasic.

Ionisation is the condition of being dissociated into ions by heart or radiation or chemical reactions or electrical discharge.

Caution: Care must be taken while mixing any concentrated inorganic acid with water. The acid must be added slowly and carefully with constant stirring to water since it generates large amount of heat. If water is added to acid, the mixture splashes out of the container and it may cause burns.

Few metals do not react with acid and liberate hydrogen gas. For example: Ag, Cu.

Role of water in acid solution: Acids show their properties only when dissolved in water. In water, they ionise to form H⁺ ions which determine the properties of acids. They do not ionise in organic solvents. For example, when HCl is dissolved in water it produces H⁺ ions and Cl^– ions whereas in organic solvents like ethanol they do not ionise and remain as molecule.

All alkalis are bases but not all bases are alkalis. For example: NaOH and KOH are alkalis whereas Al(OH) ₃ and Zn(OH) ₂ are bases.

Few metals do not react with sodium hydroxide. Example: Cu, Ag, Cr.

The term acidity is used for base, which means the number of replaceable hydroxyl groups present in one one molecule of a base.

Choose the best answers:

1. Zn + 2 HCl 🡪 ZnCl₂ + … ↑

a) H₂

b) O₂

c) CO₂

2. Apple contains malic acid. Orange contains _______________

a) Citric acid

b) ascorbic acid

3. Acids in plants and animals are organic acids. Whereas acids in rocks and minerals are ___________

a) Inorganic acids

b) weak acids

4. Acids turn blue litmus paper to ___________

a) green

b) red

c) orange

5. Since metal carbonate and metal bicarbonate are basic, they react with acids to give salt and water with the liberation of _________a) NO₂

b) SO_­2

c) CO₂

6. The hydrate salt of copper sulphate has ____________ colour

a) red

b) white

c) blue

Answers:

Choose the best answers:

1. H₂ 2. ascorbic acid 3. Inorganic acids 4. red 5. CO₂ 6. Blue