CON.H2SO4

In fact, concentrated sulphuric acid can even react with metals with low reactivity (copper and silver, but not gold and platinum), i.e. the metals located low in the reactivity series. The concentrated sulphuric acid reacts with metals to give sulphur dioxide, not hydrogen, as it is a strong oxidizing agent.

e.g. Zn (s) + 2H2SO4 (l) → ZnSO4 (aq) + SO2 (g) + 2H2O (l)

(H2SO4 in liquid state means that it is concentrated.)

When sulphuric acid is diluted, it is no longer an oxidizing agent anymore. It behaves like an acid. So, diluted sulphuric acid only react with metals which are plated higher than copper in the reactivity series, and gives hydrogen gas.

e.g. Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g)

(H2SO4 in aqueous state means that it is diluted.)

Therefore:
1. Concentrated sulphuric acid reacts with metals (X gold and platinum) to give sulphur dioxide.
2. Diluted sulphuric acid reacts with metals (higher than copper in the reativity series) to give hydrogen gas.

Ag冇反應 conc. nitric acid 先有