Question

When h2s gas is passed into a blue coloured solution a black precipitate and sulphuric acid is formed identify the orignal compound

Answer 1

Black precipitate is copper sulphide and blue coloured solution is copper sulphate

Answer 2

The blue coloured solution in which $H_{2}$ S gas is passed is Copper Sulphate          ( CuS$O_{4}$ ) solution and the black precipitate formed is Copper Sulphide ( CuS ) . It is an example of Double Displacement Reaction.