question_answer

  (i) Name a metal for each case: (a) It does not react with cold as well as hot water but reacts with steam. (b) It does not react with any physical state of water. (ii) When calcium metal is added to water the gas evolved does not catch fire but the same gas evolved on adding sodium metal to water catches fire. Why is it so?    [CBSE (AI) 2008]

Answer:

                  (i) (a) Aluminium, (b) Copper (ii)In both cases, the gas evolved is Hg. When calcium reacts with water the heat evolved is not sufficient for hydrogen to catch fire. On the other hand, sodium metal reacts with water violently and in this case a lot of heat is evolved which is sufficient for hydrogen to catch fire.