Class 10 Science

# Acids Bases and Salts

## NCERT Solution

### Part 1

Question 1: A solution turns red litmus blue, its pH is likely to be

1. 1
2. 4
3. 5
4. 10

Explanation: We know that basic solution turns red litmus to blue. We also know that the pH of basic solution is more than 7.

Question 2: A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains

1. NaCl
2. HCl
3. LiCl
4. KCl

Explanation: We know that egg shells are composed of calcium carbonate. When calcium carbonate reacts with an acid then carbon dioxide is formed. Moreover, carbon dioxide turns lime water milky. Acid is given only in option (b), so it is the correct answer.

Question 3: 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be

1. 4 mL
2. 8 mL
3. 12 mL
4. 16 mL

Explanation: It is a simple question involving ratio and proportion.

Question 4: Which one of the following types of medicines is used for treating indigestion?

1. Antibiotic
2. Analgesic
3. Antacid
4. Antiseptic

Explanation: Antibiotic is given for treating bacterial infections. Analgesic is given to subside pain. Antiseptic is given to prevent infection to a cut injury or wound.

Question 5: Write word equations and then balanced equations for the reaction taking place when

(a) Dilute sulphuric acid reacts with zinc granules.

Answer: Sulphuric acid + Zinc → Zinc sulphate + Hydrogen

Zn + H2SO4 ⇨ ZnSO4 + H2

(b) Dilute hydrochloric acid reacts with magnesium ribbon.

Answer: Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen

Mg + 2HCl ⇨ MgCl2 + H2

(c) Dilute sulphuric acid reacts with aluminium powder.

Answer: Suphuric acid + Aluminium → Aluminium sulphate + Hydrogen

2Al + 3H2SO4 ⇨ Al2(SO4 )3 + 3H2

(d) Dilute hydrochloric acid reacts with iron filings.

Answer: Sulphuric acid + Iron → Ferric chloride + Hydrogen

2Fe + 6HCl ⇨ 2FeCl3 + 3H2

Question 6: Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.

Answer: Following activity can be done for this:

• Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid, etc.
• Fix two nails on a cork, and place the cork in a 100 mL beaker.
• Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch.
• Now pour some glucose solution in the beaker and switch on the current.
• Repeat with alcohol solution and hydrochloric acid.

It is observed that bulb does not glow using glucose or alcohol solution. While if a solution of acid is used instead of glucose or alcohol solution, bulb glows.

Bulb glows when the solution of hydrochloric acid is used, because it dissociates into hydronium ion in aqueous solution. But glucose and alcohol do not dissociate hydronium ion in the water. Hence solution of glucose and alcohol do not conduct electricity.

Question 7: Why does distilled water not conduct electricity, whereas rain water does?

Answer: We know that ions are necessary for conduction of electricity through a liquid. Rain water contains acids and many other substances as impurities. These impurities produce ions in aqueous solution. On the other hand, distilled water does not contain ionic substance that can dissociate into ions. That's why rain water conducts electricity but distilled water does not do so.

Question 8: Why do acids not show acidic behaviour in the absence of water?

Answer: Hydronium ions are responsible for behavior as acid. Acids do not dissociate into hydronium ions in the absence of water, hence they do not show acidic behavior in absence of water.