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Question
Calculate total moles after dissociation in 0.1 M KCl solution and 0.05 M aluminium sulphate solution. Hence, decide which of the two solutions will have higher freezing point depression.
Solution
\[\ce{\underset{\text{0.1 M}}{KCl} -> \underset{\text{0.1 M}}{K+} + \underset{\text{0.1 M}}{Cl-}}\]
Total moles in solution = 0.2 mol
\[\ce{\underset{\text{0.05 M}}{Al2(SO4)3} -> \underset{\text{0.1 M}}{2Al^{3+}} + \underset{\text{0.15 M}}{3SO_4^{2-}}}\]
Total moles in solution = 0.25 mol
Al2(SO4)3 solution contains more number of particles than KCl solution.
Hence, Al2(SO4)3 solution has maximum ∆Tf.
Therefore, the freezing point depression of 0.05 M Al2(SO4)3 solution will be higher than 0.1 M KCl solution.
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