Foundation
Chemistry Foundation
Chemical Properties of Acids and Bases
Question
Which of the following metals liberate hydrogen with 5% HNO3?
(i) Cu (ii) Zn (iii) Mn (iv) Mg
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Solution
Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to water and is itself reduced to any of oxides of nitrogen (N2O, NO, NO2). But Mg and Mn react with very dilute HNO3 to evolve H2 gas.
Mn(s) + 2HNO3(aq) → Mn (NO3)2 (aq) + H2(g) (very dilute)