Question

Dilute and concentrated sulphuric acid can be distinguished by using metals copper and zinc. Explain by giving balanced equations.

Answer 1

Dilute and concentrated sulphuric acid can be distinguished using copper and zinc as follows:

With zinc:

Dilute sulphuric acid reacts with zinc to liberate hydrogen gas:

\[\ce{Zn + H2SO4(dil{.}) -> ZnSO4 + H2 ^}\]

Concentrated sulphuric acid acts as an oxidising agent and gives sulphur dioxide:

\[\ce{Zn + 2H2SO4(conc{.}) −> ZnSO4 + SO2 + 2H2O}\]

With copper:

Copper does not react with dilute sulphuric acid.

Copper reacts with hot concentrated sulphuric acid to liberate sulphur dioxide:

\[\ce{Cu + 2H2SO4(conc{.}) −> CuSO4 + SO2 + 2H2O}\]

Thus, dilute H₂SO₄ gives hydrogen with zinc and no reaction with copper, whereas concentrated H₂SO₄ gives sulphur dioxide with both metals.