Question

In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?
A. Lead sulphate (insoluble)
B. Lead acetate
C. Ammonium nitrate
D. Potassium sulphate

Answer 1

Hint: In double displacement reaction two aqueous solution of the chemical compounds react to form a solid compound and an aqueous solution. In this reaction replacement of ions between both the reactants compounds take place.

Complete answer:
> The double displacement reaction is defined as the reaction where the atom or ion of one reactant is replaced by the atoms or ions of the other reactant to form the product and vice-versa.
> Here, it is given that aqueous potassium iodide reacts with aqueous lead nitrate to form a yellow precipitate of lead iodide and potassium nitrate.
> The reaction between aqueous potassium iodide and aqueous lead nitrate is shown below.
$2KI(aq) + Pb(N{O_3})(aq) \to Pb{I_2}(s) + 2KN{O_3}$
> In this reaction two mole of aqueous solution of potassium iodide reacts with one mole of aqueous solution of lead nitrate to form one mole of solid lead iodide and two mole of potassium nitrate.
> In compound potassium iodide dissociates into its potassium ion and iodide ion and the compound lead nitrate dissociates into its lead ion and nitrate ion.
> The lead ion joins with the iodide ion on mixing and forms solid lead iodide and potassium ion and nitrate ion joins to form potassium nitrate.
> Lead acetate dissolves in water to give lead ion and acetate ion and on reacting with potassium iodide, the lead ion joins with the iodine ion to form lead iodide and potassium ion joins with acetate ion to form potassium acetate.
> Thus, lead acetate can be used in place of lead nitrate in this reaction.

Therefore, the correct option is B.

Note: In double displacement reaction, it is mandatory that the two reactants used should be soluble in water and be an ionic compound so that it can dissociate to give its constituent ions. The compound which is insoluble in water cannot dissociate into its ion and cannot be replaced by another ion or atom.