Question

(a) Give only one suitable chemical test to identify the following gases.

1. Ammonia
2. Sulphur dioxide
3. Hydrogen Chloride
4. Chlorine
5. Carbon Dioxide
6. Oxygen
7. Hydrogen

(b) Select a basic gas mentioned in Q.1 (a). How is the basic nature suspected?

(c)Select acidic gases from the gases mentioned in Q.1 (a). How is the acidic nature suspected?

(d) State the gas responsible for bleaching action.

(e)Which gas turn blue cobalt chloride paper light pink?

 

Answer 1

(a) (i) Chemical test for ammonia:

If a rod dipped in concentrated hydrochloric acid is brought near ammonia gas, dense white fumes of ammonium chloride (NH₄Cl) are formed.

(ii) Chemical test for Sulphur dioxide:

It decolorizes pink coloured potassium permanganate solution.

\[\ce{2KMnO4 + 2H2O + 5SO2 -> K2SO4 + 2MnSO4 + 2H2SO4}\]

(iii) Chemical test for HCl:

When HCl gas is passed through AgNO₃ solution, white precipitates of AgCl are formed which gets dissolved in excess of NH₄OH.

\[\ce{AgNO3(aq) + HCl -> AgCl ↓ + HNO3}\]

(iv) Chemical test for Chlorine:

It turns moist starch iodide paper (KI + starch solution) blue-black.

(v) Chemical test for Carbon dioxide:

When this gas is passed through lime water, it turns milky due to the formation of white precipitates of CaCO₃ and on passing excess of carbon dioxide gas, this milkiness disappears.

(vi) Chemical test for oxygen:

This gas is absorbed in a colourless alkaline solution of pyrogallol and turns it dark brown.

(vii) Chemical test for hydrogen:

It burns with a pop sound when a burning taper is brought near it.

(b)Ammonia is a basic gas and its basic nature is suspected through litmus paper test because it changes the colour of red litmus paper to blue.

(c) Chlorine, carbon dioxide, hydrogen chloride, hydrogen sulphide and sulphur dioxide are acidic gases since they convert blue litmus to red.

(d) Chlorine gas.

(e) Water vapour.