Question

Acid reacts with metals release hydrogen gas but there is one acid which when reacts with metals doesn't release hydrogen except for two metals.prove this statement

Answer 1

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Here is your answer .............


Above answer is right. Nitric acid doesn't liberate H2 gas, instead you get nitrogen oxides and water along with metal nitrate. This is because HNO3 is a powerful oxidizing agent, It oxidises the hydrogen produced to water and itself gets reduced to oxides of nitrogen such as NO , NO2 ,N2O

However dilute nitric acid reacts with Magnesium and manganese to liberate H2

 
Mg + HNO3 ------- Mg (NO3)2 + H2

From the reaction we can see that, loss of electron takes place which implies that HNO3OXIDISES Mg. Mg is reducing agent , hence hydrogen is reduced due to reducing nature of Mg .


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Answer 2

Acid + Metal → Salt + Hydrogen

e.g. 2HCl + 2Na → 2NaCl + H2

H2SO4 + 2Na → Na2SO4 + H2

HNO3 + Na → No hydrogen gas.

Because nitric acid is strong oxidizing agent and Nitric acid reacts only with Mg and Mn to give

hydrogen gas.

Mg + 2HNO3 → Mg(NO3)2 + H2

Mn + 2HNO3 → Mn(NO3)2 + H2