Question

A red-brown metal X forms a salt XSO₄. When hydrogen sulphide gas is passed through an aqueous solution of XSO₄, then a black precipitate of XS is formed alongwith sulphuric acid solution.

1. What could the salt XSO₄ be?
2. What is the colour of salt XSO₄?
3. Name the black precipitate XS.
4. By using the formula of the salt obtained in (a) above, write an equation of the reaction which takes place when hydrogen sulphide gas is passed through its aqueous solution.
5. What type of chemical reaction takes place in this case?

Answer 1

1. The salt XSO₄ is copper(II) sulphate (CuSO₄).
2. The colour of the salt CuSO₄ is blue.
3. The black precipitate XS is copper sulphide (CuS).
4. \[\ce{CuSO4_{(aq)} + H2S_{(g)} -> CuS_{(s)}\downarrow + H2SO4_{(aq)}}\]
5. A double displacement reaction or precipitation reaction takes place in this case.