Question

why does the colour of copper sulphate solution change when an iron nail is dipped in it?​

Answer 1

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When an iron nail immersed in the solution of copper sulphate than iron displaces copper from the solution of copper sulphate because iron is more reactive than copper. Therefore copper sulphate solution colour changes from blue to pale green.

Answer 2

When an iron nail is dipped in copper sulphate solution , the displacement reaction takes place . The colour of copper sulphate solution fades due to the formation of light green solution of iron sulphate .