Question

When concentrated sulphuric acid was added to an unknown salt present in a test tube a brown gas (A) was evolved. This gas intensified when copper turnings were added to this test tube. On cooling, the gas (A) changed into a colourless solid (B).

1) Identify (A) and (B).

2) Write the structures of (A) and (B).

3) Why does gas (A) change to solid on cooling?

Answer 1

1) A = NO₂  ; B = N₂O₄

2) 

3) It converts into solid because of _NO2 form dimer i.e N₂O₄ at low temperature.