Question

Give the Characteristic tests for the following gases:
(i) $C{O_2}$
(ii) $S{O_2}$
(iii) ${O_2}$
(iv) ${H_2}$

Answer 1

Hint: Hydrogen and Oxygen are one of the major components of the atmosphere. Carbon dioxide is the gas evolved due to burning of fossil fuels majorly and is one of the greenhouse gases too.

Complete answer:
The tests can be performed to identify these gases are:
For Carbon Dioxide we can use the milky water test. When the gas is passed through Lime water (Calcium Hydroxide dissolved in water) and it turns milky, indicates the presence of Carbon Dioxide. The reaction can be given as:
$Ca{(OH)_2} + C{O_2} \to CaC{O_3} + {H_2}O$
Due to the formation of Calcium Carbonate the lime water turns milky. If the gas is in excess then the milkiness will disappear with the formation of Calcium Bicarbonate.
Sulphur dioxide is a strong reducing agent hence it can turn acidic potassium permanganate, which is initially purple in colour, to colourless. The reaction can be given as:
$2KMn{O_4} + 2{H_2}O + 5S{O_2} \to {K_2}S{O_4} + 2MnS{O_4} + 2{H_2}S{O_4}$
Here ${K_2}S{O_4}$ and $MnS{O_4}$ are colourless.
Oxygen gas is very combustible; hence this property can be used to indicate its presence. When a burning candle is brought near the mouth of the test tube, the intensity of the flame will increase, if oxygen is present in the test tube.
Detection of Hydrogen is very simple. If hydrogen gas is being evolved in a chemical reaction it can be recognized by the pop sound it’ll make, when a burning candle/matchstick is brought near the mouth of the test tube.

Note:
All the given gases are colourless gases. Carbon dioxide, Nitrogen and Hydrogen are odourless gases whereas Sulphur dioxide has a very pungent and choking odour.