Question

Two salts "X" and "Y" are taken in two test tubes "A" and "B" respectively and subjected to heating Water is added to two test tubes, in case of "A" salt regains its original colour and in case of "B" water starts boiling. Then X and Y may be respectively
A. Blue vitriol and limestone
B. blue vitriol and baking soda
C. nitre and limestone
D. nitre and washing soda

Answer 1

Correct Answer - A
X is blue vitriol `CuSO_(4)*5H_(2)O` which is blue in colour. This on heating loses water of crystallization and forms anhydrous salt which is colourless. When water is added to anhydrous salt it forms copper sulphate pentahydrate which is blue in colour.
`underset("Blue")(CuSO_(4)*5H_(2)O overset("heating") rarr underset("Colourless")(CuSO_(4)) overset(+H_(2)O) rarr underset("blue")(CuSO_(4)*5H_(2)O)`
Y is limestone, `CaCO_(3)` which on heating gives CaO, It is an exothermic reaction and hence water starts boiling.