Class 10 Science Note

Some Gases

Carbon dioxide

General methods of preparation:

By burning carbon in a excess air

C +O2 → CO2

By burning organic compounds.

CH4 +2O2   →  CO2 + 2H2O + energy


Laboratory preparation of carbon dioxide

Carbon dioxide is prepared in the laboratory by reacting calcium carbonate with dil. hydrochloric acid.

Chemical Reaction:

CaCO3 + 2HCl     →     CaCl2 + H2O + CO2

First of all, pieces of limestone are taken in Wolfe's bottle and dil HCl is poured from the thistle funnel. When limestone and HCl comes in contact, the reaction occurs and CO2 gas is formed. The formed gas passes through the delivery tube to the gas jar. Since, the gas is heavier than air, it is collected by upward displacement of air.


Physical properties of Carbon dioxide are:

1. It is colorless, odourless and tasteless gas.

2. It is heavier than air.

3. It dissolves in water.

4. It turns wet blue litmus paper into red.


Chemical properties of carbon dioxide are:

When CO2 gas reacts with lime water, then it forms calcium carbonate and the solution turns lime water milky.
Ca(OH)2 + CO2 → CaCO3 + H2O

When carbon dioxide is passed into lime water for a long time, then the milky solution turns into colorless.
CaCO3 + H2O + CO2 → Ca (HCO3)2

The process by which plants make the food with the help of sunlight is called photosynthesis.

6CO2 + 6H20   →sunlight  C6H12O6 + 6O2



1. Carbon dioxide is used by all green plants during photosynthesis.

2. It is used as fire extinguishers.

3. It is used for making dry ice to preserve meat, fruits etc

4. It is also used in the process of carbonation in industries.

5. It is used for making soft drinks like beer, coca cola, soda etc.



General methods of preparation:

Heating ammonium salts

(NH4)2SO4 2 NH3 + H2SO4

Heating ammonium salts with strong base

When the mixture of sodium hydroxide and ammonium sulphate is heated, then there is the formation of ammonia gas.
(NH4)2SO4 + 2NaOH → Na2SO4 + 2H2O + NH3


Laboratory preparation of ammonia gas.



When a crushed mixture of ammonium chloride is heated with calcium hydroxide, then ammonia produced.

2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3

For the preparation of ammonia gas, first of all a mixture of ammonium chloride and slaked lime is taken in a hard glass tube. The test tube is hold by a stand in inclined position. The delivery tube is fixed on the opening of the test tube which is connected to lime tower. Above lime tower inverted delivery tube is kept. When the mixture is heated, ammonia gas is liberated which passes through lime tower inside the delivery tube. Since ammonia is lighter than air, it is collected by downward displacement of air.


The test of ammonia gas can be done in following ways:

I. It changes red litmus into blue.

II. It can be identified by its pungent smell.

III. When it is reacted with HCl, it forms ammonium chloride.


Manufacture of ammonia (Habers synthesis process)

In the industrial sector, ammonia is manufactured at the Haber's synthesis process. In this process, nitrogen and hydrogen are heated in the ratio of 1:3 in the presence of iron as catalyst and molybdenum as promoter at temperature of about 500oC, under high pressure of about 200 - 900 atmospheric pressure. 
N2 + 3H2 ↔ 2NH3
It is essential for production of ammonia at large quantity because it is a reversible process. Since it is reversible, after a certain time product will form the reactants itself, so less reactant is consumed. Along with that it is an exothermic reaction, so less heat is required.


I. It is used in preparation of chemical fertilizers.
II. It is also used for the production of nylons and rayons.

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