Calculate the molality of nonvolatile solution if solution freezes at − 0.9 5 ∘ C [ K f for water = 1.86 K kg mol − 1 , freezing point of water = 0 ∘ C ]

Question

Calculate the molality of nonvolatile solution if solution freezes at − 0.9 5 ∘ C [ K f ​ for water = 1.86 K kg mol − 1 , freezing point of water = 0 ∘ C ]

TestHub · Accepted Answer

The depression in freezing point is given by $Δ T_{f} = T_{f}^{\circ} - T_{f}$

$Δ T_{f} = 0^{\circ} C - (- 0.9 5^{\circ} C) = 0.9 5^{\circ} C = 0.95 K$

The relation between depression in freezing point and molality is $Δ T_{f} = K_{f} \times m$

$m = \frac{Δ T _{f}}{K _{f}}$

$m = \frac{0.95}{1.86}$

$m = 0.51 mol kg^{- 1}$

Answer: $0.51 mol kg^{- 1}$

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