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Standard XII

Chemistry

Depression in Freezing Point

Calculate the...

Question

Calculate the density of glycol solution whose $2.976 L$ on addition to $5 L$ of water produce an antifreeze which protects automobile radiator down to $- 20^{o} C$ . . $K_{f}$ and $K_{B}$ for water are $1.86$ and $0.51 K$ $m o l^{- 1}$ kg respectively. Answer should be the nearest integer value.

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Solution

The depression in the freezing point $Δ T_{f} = 0 - (- 20) = 20^{o} C$
The molality of solution $m = \frac{Δ T_{f}}{K_{f}} = \frac{20}{1.86} = 10.75 m$
1 kg (or 1000 g) of water contains 10.75 moles of glycol.
5 litre (or 5 kg) of water will contain $5 \times 10.75 = 53.76$ moles of glycol. The molar mass of glycol is 62 g/mol. Mass of glycol $= 53.76 \times 62 = 3333.3 g$
Total mass of solution $= 3333.3 + 5000 = 8333.3 g$
Total volume $= 2976 + 5000 = 7976$
Density $= \frac{m a s s}{v o l u m e} = \frac{8333.3}{7976} = 1.12 g / m L$

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Calculate the density of glycol solution whose 2.976L on addition to 5L of water produce an antifreeze which protects automobile radiator down to −20oC. . Kf and KB for water are 1.86 and 0.51 K mol−1 kg respectively. Answer should be the nearest integer value.

Calculate the density of glycol solution whose $2.976 L$ on addition to $5 L$ of water produce an antifreeze which protects automobile radiator down to $- 20^{o} C$ . . $K_{f}$ and $K_{B}$ for water are $1.86$ and $0.51 K$ $m o l^{- 1}$ kg respectively. Answer should be the nearest integer value.