Question

When sodium hydroxide is added to ferric chloride solution, a reddish brown precipitate is formed. The precipitate is separated from the mixture by the process of:
a) Filtration
b) Distillation
c) Sublimation
d) Chromatography

Answer 1

Hint: Filtration is the method by which insoluble substances can be separated out from a solution. The insoluble particles left on the paper are called residue and the liquid that passed through is known as filtrate.

Complete step by step solution:
Iron shows most commonly two oxidation states, i.e. $ + 2 $ and $ + 3 $ . In the higher oxidation state the name is given as Ferric and in the lowest oxidation state the name is given as Ferrous.
In the given question Ferric chloride is used in the reaction. It is used in sewage treatment, industrial waste, for purification of water, etc. Its solution appears as colourless but with the time it changes to slightly brown and gives a smell of hydrochloric acid.
When ferric chloride ( $ FeC{l_3} $ ) reacts with sodium hydroxide it forms a precipitate of ferric hydroxide. The reaction can be represented as –
 $ FeC{l_3} + 3NaOH \to Fe{(OH)_3} \downarrow + 3NaCl $
We can see here that to balance the Valency of ferric ions three moles of hydroxide ions are needed. The precipitate is reddish brown ( $ Fe{(OH)_3} $ ) in colour. As iron belongs to the transition metal series, it gives colour to its compounds.
The precipitate is deposited at the bottom of the container. And so by using a very easy technique, i.e. filtration the precipitate can be separated from the solution.
When we pass the solution from one container to another through a funnel covered with filter paper, the reddish brown precipitate can be easily seen while separating.
$ \therefore $ The correct option is (a).

Note:
Ferric chloride ( $ FeC{l_3} $ ) very importantly used in the qualitative analysis of function groups. This is used to detect phenols from the sample as on reaction with phenol it gives a violet coloration due to formation of a complex. It reacts with different substituted phenols also and gives different colours.