Question

colourless concentrated sulphuric acid in a test tube changes to blue on adding a small piece of copper to it

Answer 1

H2SO4 + Cu --------> CuSO4 + H2

copper displaces hydrogen. Hence it is a displacement reaction.

Answer 2

Answer:

Colourless concentrated sulphuric acid in a test tube changes to blue an adding a small piece of copper to it because copper displaces hydrogen present in sulphuric acid. as copper attributes blue colour the acid turns blue.

Explanation:

Thus occurs a redox reaction leaving CuSo4 and sulphur dioxide and water as end products.

2H2SO4      +     Cu (s)       →       CuSo4       +      SO2      +      2H2O

concentrated     copper             Copper            sulphur            water

sulphuric acid                              sulphate          dioxide