Question

metal salt A is blue in color. When salt A is heated strongly, then a substance B is eliminated

and a white powder C is left behind. When a few drops of a liquid D are added to powder C, it

becomes blue again.

a) Identify A, B, C and D [2]

b) Write the chemical equations involved [2]

c) Give an example of one more salt which shows the above property. [1]​

Answer 1

On heating:

Copper sulphate crystals (A) are blue. When copper sulphate crystals are heated strongly, they lose all the water of crystallisation (B) and form anhydrous copper sulphate (C), which is white.

$CuSO_{2}.5H_{2}O → CuSO_{4}+ 5H_{2}O$

On adding few drops of water:

Anhydrous copper sulphate turns blue on addition of a few drops of water (D) because it gets hydrated again.

$CuSO_{4}+ 5H_{2}O→CuSO_{2}.5H_{2}O$

______________________________

(a)

A = Crystals of copper sulphate.

B = Water

C = Anhydrous copper sulphate.

D = Water

(b)

Anhydrous copper sulphate turns blue on addition of a few drops of water (D) because it gets hydrated again.

$CuSO_{4}+ 5H_{2}O→CuSO_{2}.5H_{2}O$

(c)

Ferrous sulphate

Answer 2

Answer:

A is copper sulphate pentahydrate, CuSO4.5H2O.

B is water, H2O.

C is anhydrous copper sulphate, $$

D is water, H2O

On heating: CuSO4.5H2OHeatCuSO4+H2O

                             A                                  C           B

On adding few drops of water: CuSO4+5H2O→CuSO4.5H