Question

When $KI$ -solution is added to a solution of lead (II) nitrate \[\left( {Pb{{\left( {N{O_3}} \right)}_2}} \right)\] in a test tube, a precipitate is formed.
(i) What is the colour of this precipitate?
(ii) Name the compound precipitated.
(iii) Write the balanced chemical equation for this reaction.
(iv)What type of reaction is this?

Answer 1

Hint: We need to understand the complete reaction between potassium iodide and lead (II) nitrate. The reaction needs to be thoroughly studied to predict the colour of the precipitate formed, the name of the compound which gets precipitated, the complete chemical equation which needs to be balanced and the type of reaction.

Complete answer:
We have to know that potassium iodide reacts with lead nitrate under aqueous conditions and the following is observed about the reaction:
(i).When KI-solution is added to a solution of lead (II) nitrate \[\left( {Pb{{\left( {N{O_3}} \right)}_2}} \right)\] in a test tube, the precipitate is yellow in colour.
(ii)When KI-solution is added to a solution of lead (II) nitrate \[\left( {Pb{{\left( {N{O_3}} \right)}_2}} \right)\] in a test tube, a precipitate $Pb{I_2}$ is formed. The name of this precipitate is lead iodide.
(iii).The balanced chemical equation for the reaction when KI-solution is added to a solution of lead (II) nitrate\[\left( {Pb{{\left( {N{O_3}} \right)}_2}} \right)\] is as follows:
\[Pb{\left( {N{O_3}} \right)_2}_{\left( {aq} \right)} + 2KI\left( {aq} \right) \to Pb{I_2} \downarrow + 2KN{O_{3\left( {aq} \right)}}\]
(iv).A reaction in which KI-solution is added to a solution of lead (II) nitrate \[\left( {Pb{{\left( {N{O_3}} \right)}_2}} \right)\] where lead iodide is formed as a precipitate is called a precipitation type of reaction.

Note:
We must be noted that the reaction in which KI-solution is added to a solution of lead (II) nitrate \[\left( {Pb{{\left( {N{O_3}} \right)}_2}} \right)\] where lead iodide is formed as a precipitate can also be considered as a double displacement reaction. Double displacement reactions are those in which two compounds react by exchanging ions to produce two new compounds. Precipitate is usually formed as a result of a double displacement reaction. Covalent or ionic chemical bonds may form between the reactants.