Page No 16: - Chapter 1 Chemical Reactions & Equations class 10 ncert solutions Science - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Question 12:

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Answer:

(a) Thermal decomposition:

(b) Decomposition by light:

(c) Decomposition by electricity:

Question 13:

What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Answer:

In a displacement reaction, a more reactive element replaces a less reactive element from a compound.

 where A is more reactive than B

In a double displacement reaction, two atoms or a group of atoms switch places to form new compounds.

For example:

Displacement reaction:

Double displacement reaction:

Question 14:

In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Answer:

Question 15:

What do you mean by a precipitation reaction? Explain by giving examples.

Answer:

A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.

For example:

In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction.

Another example of precipitation reaction is:

In this reaction, barium sulphate is obtained as a precipitate.

Question 16:

Explain the following in terms of gain or loss of oxygen with two examples each.

(a) Oxidation

(b) Reduction

Answer:

(a) Oxidation is the gain of oxygen.

For example:

(i) 

(ii) 

In equation (i), H₂ is oxidized to H₂O and in equation (ii), Cu is oxidised to CuO.

(b) Reduction is the loss of oxygen.

For example:

(i) 

(ii) 

In equation (i), CO₂ is reduced to CO and in equation (ii), CuO is reduced to Cu.

Question 17:

A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

Answer:

‘X’ is copper (Cu) and the black-coloured compound formed is copper oxide (CuO). The equation of the reaction involved on heating copper is given below.

Question 18:

Why do we apply paint on iron articles?

Answer:

Iron articles are painted because it prevents them from rusting. When painted, the contact of iron articles from moisture and air is cut off. Hence, rusting is prevented. So presence of air and moisture is essential for rusting to take place.

Question 19:

Oil and fat containing food items are flushed with nitrogen. Why?

Answer:

Nitrogen is an inert gas and does not easily react with these substances. On the other hand, oxygen reacts with food substances and makes them rancid. Thus, bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack. When oxygen is not present inside the pack, rancidity of oil and fat containing food items is avoided.

Question 20:

Explain the following terms with one example each.

(a) Corrosion

(b) Rancidity

Answer:

(a) Corrosion:

Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc.

For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide.

This hydrated iron oxide is rust.

(b) Rancidity:

The process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity.

For example, the taste and smell of butter changes when kept for long.

Rancidity can be avoided by:

1. Storing food in air tight containers

2. Storing food in refrigerators

3. Adding antioxidants

4. Storing food in an environment of nitrogen