Question

To an aqueous solution of NaI, increasing amounts of solid $Hg{I}_2$ is added.The vapour pressure of the solution

• A. decreases to a costant value
• B. increases to a constant value
• C. increases and then decreases
• D. remains constant as $Hg{I}_2$ is sparingly soluble in water

Answer 1

Answer: (D)

remains constant as $Hg{I}_2$ is sparingly soluble in water

$2NaI+Hg{I}_2⟶{Na}_{2}Hg{I}_4$
As $Hg{I}_2$ is added,the number of molecules will decrease due to the formation of ${Na}_{2}Hg{I}_4$.
Therefore,pressure will increase. As more $Hg{I}_2$ is added, pressure will remain constant (and NaI is consumed) after that as $Hg{I}_2$ is sparingly soluble.