NCERT Class X Science Class: Chapter –1. Chemical Reactions and Equations – Part-7

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Question 32:

A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.


The substance

X is calcium oxide also called quicklime.

Ca is also present in our bones.

It is Calcium Hydroxide. And all hydroxides are bases ie., can turn red litmus paper blue.

Question 33:

Write a balanced chemical equation for each of the following reactions and also classify them.

  1. Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.

  2. A piece of sodium metal is added to absolute ethanol to form sodium methoxide and hydrogen gas.

  3. Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.

  4. Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.


  1. This is a double displacement as well as precipitation reaction.

  1. This is displacement reaction

  1. This is Redox reaction

  1. This is Redox reaction

Question 34:

Why do we store silver chloride in dark coloured bottles?


Dark coloured bottles interrupt the path of light such that light cannot reach silver chloride in the bottles and its decomposition is prevented. It is known that silver chloride decomposes to silver and chlorine in the presence of light.

This is shown in the reaction given below:

Silver chloride on exposure to sunlight may decompose as per the following reaction.

Therefore, it is stored in dark coloured bottles.

Question 35:

Balance the following chemical equations and identify the type of chemical reaction.


  1. Balanced; Combination reaction

  1. This is a thermal decomposition reaction as well as reduction reaction.

  1. This is combination reaction

  1. This is displacement reaction

  1. This is combination reaction

  1. This is a photochemical decomposition reaction

Question 36:

A magnesium ribbon is burnt in oxygen to give a white compound

X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.

  1. Write the chemical formulae of X and Y

  2. Write a balanced chemical equation, when X is dissolved in water


Compound [Magnesium Oxide]

Compound [Magnesium Nitride]

If "X", that is , Magnesium Oxide is dissolved in water , the product is Magnesium Hydroxide