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

In this reaction, there is a mutual exchange of ions between the two reacting compounds in their aqueous solutions:

1. Sodium sulphate dissociates into sodium ions ($\text{Na}^+$) and sulphate ions ($\text{SO}_4^{2-}$).
2. Barium chloride dissociates into barium ions ($\text{Ba}^{2+}$) and chloride ions ($\text{Cl}^-$).
3. The barium ions ($\text{Ba}^{2+}$) react with sulphate ions ($\text{SO}_4^{2-}$) to form barium sulphate ($\text{BaSO}_4$), which is highly insoluble in water and precipitates out as a white solid.
4. The sodium ions ($\text{Na}^+$) and chloride ions ($\text{Cl}^-$) remain in the solution as dissolved sodium chloride ($\text{NaCl}$).

Because there is an exchange of ions between the reactants to form new products, it is classified as a double displacement reaction. Since a solid precipitate is formed, it is also a precipitation reaction.