Question

-Separate samples of anhydrous copper $(II)$ sulphate and hydrated copper $(II)$ sulphate are heated.
Which row shows the correct color changes?
A.Anhydrous copper $(II)$ sulphate – blue to white, hydrate copper $(II)$ sulphate – white to blue
B.Anhydrous copper $(II)$ sulphate –no change, hydrate copper $(II)$ sulphate –blue to white
C.Anhydrous copper $(II)$ sulphate –white to blue, hydrate copper $(II)$ sulphate –blue to white
D.Anhydrous copper $(II)$ sulphate –white to blue, hydrate copper $(II)$ sulphate –no change

Answer 1

Hint: At first think about the color of copper sulphate. Hydrated copper sulphate is nothing but copper sulphate pentahydrate . The chemical formula of copper sulphate pentahydrate is given as $CuS{O_4}.5{H_2}O$.

Complete step by step answer:
We all know that copper sulphate pentahydrate is blue in colour. Hydrated copper sulphate is blue in color due to the water of crystallization. After heating the hydrated copper sulphate compound it loses its water of crystallization and then converts into anhydrous copper sulphate. The anhydrous copper sulphate compound is white in color. So the hydrated copper sulphate on heating changes its color from blue to white. On further heating, the anhydrous copper sulphate undergoes a decomposition reaction. The anhydrous copper sulphate powder is light grey in color. The overall reaction is given as,
$2CuS{O_4}\xrightarrow{\Delta }2CuO + 2S{O_2} + {O_2}$
From the above reaction we can say that anhydrous copper sulphate on heating gives copper oxide along with sulphur dioxide and oxygen gases. Copper oxide is black in color. So the answer is B.
So the correct option is B.
Additional Information:-The copper sulphate is produced industrially by treating copper metal with hot concentrated sulphuric acid or its oxides with dilute sulphuric acid. It can also be produced by slowly leaching low grade copper ore in air.

Note:
Copper sulphate pentahydrate is the most commonly encountered salt and it exothermically dissolves in water to give the aquo complex which has the octahedral molecular geometry. Copper sulphate is also known as blue vitriol, bluestone etc.