A student was given a crystalline salt 'B' for analysis which was blue in colour. He added a few drops of dense oily hygroscopic liquid to it and observed a colourless neutral gas/vapour being released and the salt turning white.
(a) Identify the blue crystalline salt B.
(b) Which property of the hygroscopic liquid is demonstrated in this reaction?
(c) Write a balanced chemical equation for the above reaction.
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(a) The blue crystalline salt B is copper(II) sulphate pentahydrate, CuSO4·5H2O.
(b) The dehydrating property of the hygroscopic liquid (concentrated sulphuric acid) is demonstrated, as it removes the water of crystallisation from the blue salt, leaving behind white anhydrous copper sulphate.
(c) CuSO4·5H2O $\xrightarrow{\text{conc. H}_2\text{SO}_4}$ CuSO4 + 5H2O