What happens when a solution of sodium sulphate is added to a solution of barium chloride taken in a test tube? Write an equation for the chemical reaction involved and name this type of reaction in this case.

Hint: The substances that undergo chemical change in the reaction are the reactants , and the new substance formed during the reaction, and are called products.Barium chloride and Sodium sulphate undergo precipitation reaction.A precipitation reaction is the one where one of the products formed are insoluble in water and is precipitated out.

Complete step by step answer: When sodium sulphate gets added to the barium chloride solution , the formation of white substance will be observed. This white substance will be insoluble in water . The insoluble white substance is known as precipitate. Any reaction that produces precipitate is called a precipitation reaction.
The white precipitate of barium sulphate is formed by the reaction between $S\mathop O\nolimits_4^{2 - } and$ $B\mathop a\nolimits^{2 + } $
The other product formed is sodium chloride which will remain dissolved in the solution.
The reaction that occurs in this case where there is an exchange of ions between reactants is called double displacement reaction. It is an instantaneous process.
$N\mathop a\nolimits_2S\mathop O\nolimits_4(aq) + BaC\mathop l\nolimits_2(aq) \to BaS\mathop O\nolimits_4(s) + 2NaCl(aq)$
This is known as double displacement reaction.

Note:There are many types of reactions namely:-
- Combination reaction:- the reaction in which two reacts combine to give a product.
- Decomposition:- the reaction in which a reactant breaks down to give two or more products.
- Displacement:- the reaction in which one element is replaced by another element.