Question

(a) What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which reaction between them will not take place. Write the balanced chemical equation for the reaction and also mention the type of reaction.

(b) What changes in the colour of iron nails and copper sulphate solution do you observe after keeping the iron nails in copper sulphate solution for about half an hour ?

Answer 1

(a) When barium chloride solution is added to sodium sulphate solution, then a white precipitate of barium sulphate is formed along with sodium chloride solution :

$\begin{array}{cccc}& & & \\ BaC{l}_2\left(aq\right)& +& N{a}_{2}S{O}_4\left(aq\right)⟶& \\ \text{(Barium chloride)}& & \text{(Sodium sulphate)}& \\ & & BaS{O}_4\left(s\right)\downarrow +& 2NaCl\left(aq\right)\\ & & \text{(Barium}& \text{(Sodium}\\ & & \text{sulphate}& \text{Chloride)}\\ & & \text{(white ppt.)}& \end{array}$

Reaction will not take place if the reactants are in a solid state. This is a double displacement reaction.

(b) When iron nails are dipped in copper sulphate solution, then iron sulphate solution and copper metal are formed :

$\begin{array}{cccc}& & & \\ CuS{O}_4\left(aq\right)+& Fe\left(s\right)⟶& FeS{O}_4\left(aq\right)+& Cu\left(s\right)\\ \text{Copper}& \text{Iron}& \text{Iron}& \text{Copper}\\ \text{Sulphate}& & \text{Sulphate}& \\ \text{(Blue}& \text{(Grey)}& \text{(Greenish}& \text{(Reddish}\\ \text{solution)}& & \text{solution)}& \text{brown)}\end{array}$

This displacement reaction occurs because iron is more reactive than copper. Also a reddish brown substance will be deposited on the iron nail. This substance is nothing but copper metal.