Question

17. If molality of methanol in water is 5 then the mass
percentage of methanol in the solution is
(1) 21.5%
(2) 10,5%
(3) 13.8%
(4) 27.2%

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Answer 1

Use tricks while solving

Answer 2

Answer: The mass percent of methanol is 13.8 %.

Explanation:

Given : Molality of methanol= 5  i.e. 5 moles of methanol are dissolved in 1 kg of solvent.

Mass of methanol=$moles\times {\text {Molar mass}}=5\times 32=160g$

Thus mass of solution = mass of solute + mass of solvent= 160 +1000 =1160 g

To calculate the mass percent of methanol in a given compound, we use the formula:

$\text{Mass percent of methanol}=\frac{\text{Mass of methanol}}{\text{Mass of solution}}\times 100$

Mass of methanol= 160 g

Mass of solution= 1160 g

Putting values in above equation, we get:

$\text{Mass percent of methanol}=\frac{160}{1160}\times 100=13.8\%$

Hence, the mass percent of methanol is 13.8 %.