Question

What would you observe when crystals of copper (II) sulphate and iron (II) sulphate are separately heated in two test tubes ?

Answer 1

Action of heat on copper (II) sulphate crystals

When copper (II) sulphate crystals are heated in a hard glass test tube, the following observations are made.

1. The crystals are converted into a powdery substance.
2. The crystals lose their blue colouration on further heating.
3. Steaming vapour is produced inside the tube which condenses near the mouth of the tube to form a colourless liquid.
4. On further heating, steams escapes from the mouth of the tube and water gets collected in a beaker placed under the mouth of the tube.
5. On further heating, the residue changes to a white powder and steam stops coming out.

$CuS{O}_4.5H_{2}O$ $\stackrel{heat}{\to }$ $CuS{O}_4$ + $5H_{2}O$

The action of heat on iron (II) sulphate

When iron (II) sulphate is heated in a test tube, the following observations are made.

1. The crystals crumble to white powder and a large amount of steam and gas are given out.
2. On strong heating, a brown residue of ferric oxide (Fe₂O₃) is produced and a mixture of SO₂ and SO₃ is given off.

$FeS{O}_4.7H_{2}O$ $\stackrel{heat}{\to }$ $FeS{O}_4$ + $7H_{2}O$

$2FeS{O}_4$ $\underset{\left(Brownresidue\right)}{\overset{ferricoxide}{\to }}$ $F{e}_2{O}_3$ + $S{O}_2$ + $S{O}_3$