Question

When mercuric iodide in added to the aqueous solution of potassium iodode
A. freezing point is lowered
B. freezing point is raised
C. boiling point is lowered
D. both (2) and (3)

Answer 1

Correct Answer - 4
`2KI(aq) rarr 2K^(+)(aq)+2I^(-)(aq)`
`HgI_(2)+2I^(-) rarr [HgI_(4)]^(2-)(aq)`
`2KI+Hg I_(2) overset(H_(2)O)(rarr) 2K^(+)(aq)+[HgI_(4)]^(2-)(aq)`
Due to complex ion formation between mercuric iodide and `I^(-)`, the number of moles of particles decreases from 4 to 3. Thus the magnitude of colligative properties `(DeltaT_(f) and DeltaT_(b))` decreases. Hence the freezing point is raised while the boiling point is lowered.