What do you mean by a precipitation reaction? Explain by giving examples.
A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.
For example :
$\mathop {N{a_2}C{O_{3(aq)}}}\limits_{{\text{Sodium carbonate}}} + \mathop {CaC{l_2}_{(aq)}}\limits_{{\text{Calcium chloride}}} \to \mathop {CaC{O_3}_{\left( s \right)}}\limits_{{\text{Calcium}}\,{\text{carbonate}}} + \mathop {2NaC{l_{(aq)}}}\limits_{{\text{Sodium}}\,{\text{chloride}}\,\,} $
In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction.
Another example of precipitation reaction is :
$\mathop {N{a_2}S{O_{4(aq)}}}\limits_{{\text{Sodium sulphate}}} \, + \mathop {\,BaC{l_2}_{(aq)}\,}\limits_{{\text{Barium chloride}}} \to \,\mathop {BaS{O_{4(s)}}}\limits_{{\text{Barium sulphate}}} \, + \,\mathop {2NaC{l_{(aq)}}\,}\limits_{{\text{Sodium chloride}}} $
In this reaction, barium sulphate is obtained as a precipitate.
Write the balanced equation for the following chemical reactions.
$(i)$ Hydrogen $+$ Chlorine $\to $ Hydrogen chloride
$(ii)$ Barium chloride $+$ Aluminium sulphate $\to $ Barium sulphate $+$ Aluminium chloride
$(iii)$ Sodium $+$ Water $\to $ Sodium hydroxide $+$ Hydrogen
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