Question

When mercuric iodide is added to the aqueous solution of potassium iodide

• A. freezing point is raised
• B. freezing point is lowered
• C. freezing point does not change
• D. boiling point does not change

Answer 1

Answer: (A)

freezing point is raised

Answer 2

Addition of Hgl$_2$ to KI solution establishes the following equilibrium:
$\, \, \, \, \, \, \, \, \, \, \, \, HgI_2 +2KI \rightleftharpoons K_2[HgI_4]$
The above equilibrium decreases the number of ions (4 ions on left side of reactions becomes three ions on right side), hence rises the freezing point.