Question

(1.) Explain why nitric acid is not used to dry hydrogen?

(2.) When hydrogen is burnt,why droplets of colourless liquid condense?

(3.) Explain why concentrated sulphuric acid is not used to dry hydrogen?

Answer 1

1) ​Nitric acid is a strong acid and a strong oxidising agent. It acts as oxygen source to flammable or combustible substances, causing the combustion reactions hotter and faster. And we know hydrogen gas is highly flammable substance. If nitric acid used for drying hygrogen gas there would be an exploision.
2) Pure H₂ when burns in air it produce a colourless liquid called water. The water condense as reaction is exothermic so the heat is given out to the surrounding bringing the temperature down for experimental set up.
2H₂ + O₂ $\to$2H₂O (water, colourless liquid)
3) Connentrated H₂SO₄ is also a strong acid and strong ​oxidising agent. So the reason is similar as nitric acid.