which of the following reaction can give hydrogen gas.

(1)Zn + conc.H2SO4

(2)Cu + dil. H2SO4

(3)Mn + very dilute HNO3

(4)pb + dil HNO3


Plzzzz explain all options....Thanks!!

Asked by jhajuhi19 | 13th Jun, 2019, 07:56: PM

Expert Answer:

Zinc reacts with sulphuric acid to form metal sulphate and hydrogen gas.
 Zn + H2SO4 → ZnSO4 + H
And Copper does not reacts with the dilute H2SO4 
Metals also react with nitric acid, but hydrogen gas is not evolved, because nitric acid is a strong oxidising agent. So, it oxidises the hydrogen to water and itself gets reduced to any nitrogen oxide.
However, magnesium and manganese react with very dilute nitric acid to evolve hydrogen gas.
Mg + 2HNO3 → Mg(NO3)2 + H2
Mn + 6HNO3 → Mn(NO3)2 + H2
When Lead reacts with dilute HNO3 gives redox reaction but no hydrogen gas is evolved as a product.
Pb + HNO3 → Pb(NO3)2 + NO + H2O

Hence the correct options are A and C.

Answered by Ramandeep | 14th Jun, 2019, 11:08: AM