Question

In double decomposition reactions __________ are exchanged.

Answer 1

A chemical reaction in which the constituents (cations and anions) of two compounds are mutually exchanged. Moreover, they mutually exchange their places to form two new compounds called double decomposition reactions.

Complete step by step answer: A type of chemical change in which two compounds in a solution reacts to form new compounds by the mutual exchange of radials. Generally, solid is formed as a result.
Double decomposition reaction has two types:
- Precipitation reaction: The insoluble solid formed during double displacement reaction is called precipitate. So, the reactions in which a precipitate is formed as one of the products are called precipitation reactions.
- Example: $N{a_2}S{O_4}(aq) + BaC{l_2} \to BaS{O_4}(S) + 2NaCl{(aq)_{}}$
- Sodium sulphate reacts with barium chloride to form barium sulphate and sodium chloride solution.

- Neutralisation reaction: The reaction between an acid and a base to form salt and water is called neutralisation reaction.
- Example: $NaOH (aq) + HCl (aq) \to NaCl (aq) + H_{2}O(l)$
- Sodium hydroxide (an alkali) to form sodium chloride (salt) and water in liquid form.

-Double decomposition generally takes place in between the ionic compounds. We should know that most of the precipitation reactions of ionic compounds come under the class of double decomposition reactions.

- Let us take an example
$BaCl_{2}(aq) + BaSO_{4}(aq) \to BaSO_{4}(s) + 2NaCl(aq)$
- In this reaction, two substances i.e. $BaC{l_2}$and $N{a_2}S{O_4}$react to form two products i.e. $BaS{O_4}$ and $NaCl$. The cation $B{a^{2 + }}$ and $N{a^ + }$ of the reactants exchange their partners $C{l^ - }$ and $$$$$SO_4^{2 - }$ respectively with each other during the reaction.
So answer is that, in double decomposition reaction, the constituents (cations and anions) are exchanged.

Note: As the constituents are getting exchanged or replaced, the double decomposition is also known as double replacement reaction or metathesis reaction.