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Standard XII

Chemistry

Depression in Freezing Point

A certain sub...

Question

A certain substance 'A' tetramerises in water to the extent of $80 %$ . A solution of $2.5$ g of $A$ in $100$ g of water lowers the freezing point by ${0.3}^{o} C$ . The molar mass of A is:

122

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31

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244

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62

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Solution

The correct option is D $62$
$α = \frac{1 - i}{1 - \frac{1}{n}}$
$0.8 = \frac{1 - i}{1 - \frac{1}{4}}; i = 0.4$
$△ T = i K_{f} \times m$
$0.3 = 0.4 \times 1.86 \times \frac{w_{B} \times 1000}{m_{B} \times w_{A}}$
$0.3 = 0.4 \times 1.86 \times \frac{2.5 \times 1000}{m_{B} \times 100}$
$m_{B} = 62$

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A certain substance 'A' tetramerises in water to the extent of 80%. A solution of 2.5 g of A in 100 g of water lowers the freezing point by 0.3oC. The molar mass of A is:

The correct option is D 62α=1−i1−1n0.8=1−i1−14;i=0.4△T=iKf×m0.3=0.4×1.86×wB×1000mB×wA0.3=0.4×1.86×2.5×1000mB×100mB=62

A certain substance 'A' tetramerises in water to the extent of $80 %$ . A solution of $2.5$ g of $A$ in $100$ g of water lowers the freezing point by ${0.3}^{o} C$ . The molar mass of A is: