JEE Advance - Chemistry (1980 - No. 17)
Explain the following in not more than two sentenses.
A solution of FeCl3 in water gives a brown precipitate on standing.
FeCl3 reacts with water to form iron(II) hydroxide, which is a brown precipitate.
FeCl3 hydrolyzes in water, producing HCl and a brown precipitate of Fe(OH)3.
FeCl3 oxidizes in water to form iron(IV) oxide, which is the brown precipitate.
FeCl3 forms a complex with water molecules, resulting in a brown colored solution that eventually precipitates.
The brown precipitate is due to the presence of impurities in the FeCl3 salt, which react with water over time.
Explanation
$\mathrm{FeCl}_3$ is a salt of strong acid and weak base. In water, it hydrolyses slowly producing brown ppt of $\mathrm{Fe}(\mathrm{OH})_3$.
$$ \mathrm{FeCl}_3+3 \mathrm{H}_2 \mathrm{O} \longrightarrow 3 \mathrm{HCl}+\mathrm{Fe}(\mathrm{OH})_3 \downarrow $$(Brown)
$$ \mathrm{FeCl}_3+3 \mathrm{H}_2 \mathrm{O} \longrightarrow 3 \mathrm{HCl}+\mathrm{Fe}(\mathrm{OH})_3 \downarrow $$(Brown)
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