Question

$25 \,mL$ of an aqueous solution of $KCl$ was found to require $20\, mL$ of $1\, M$ $AgNO _3$ solution when titrated using $K _2 CrO _4$ as an indicator What is the depression in freezing point of $KCl$ solution of the given concentration? _________ (Nearest integer) (Given: $K _f=20 \,K \,kg \,mol ^{-1}$ )

Assume 1) $100 \%$ ionization and

2. density of the aqueous solution as $1 \,g \,mL ^{-1}$

Answer 1

The correct answer is 3

At equivalence point,
mmole of KCl= mmole of AgNO3​
=20m mole
Volume of solution =25ml
Mass of solution =25gm
Mass of solvent
=25− mass of solute
=25−[20×10−3×74.5]
=23.51gm
Molality of KCl= mass of solvent in kg mole of KCl​
=23.51×10−320×10−3​=0.85
i of KCl=2(100% ionisation )
ΔTf​=i×Kf​×m
=2×2×0.85
=3.4
≈3