Question

Give two tests for each of the following:
(a) NH₃
(b) Oxygen
(c) Water vapour

Answer 1

(a) NH₃ (Ammonia)

• It turns moist red litmus blue.
• On bringing a glass rod dipped in conc. HCl near the gas, dense white fumes are produced.

NH₃(g) + HCl (aq) → NH₄Cl (g)

• It turns the filter paper dipped in nessler's reagent brown.

NH₃ + 3KOH + 2K₂HgI₄ → NH₂Hg₂OI + 7KI + 2H₂O

Disclaimer: There are more tests for ammonia gas than listed above. Any two of the tests can be used to answer the given question.

(b) Oxygen

• It rekindles a glowing splinter.
• It turns alkaline pyrogallol brown.

(c) Water vapour

• It does not change the colour of the litmus paper.
• It turns white anhydrous copper sulphate blue after condensing on a cool surface to form clear droplets.