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(B) Molality $(m)$ is defined as the number of moles of solute per kilogram of solvent. For pure water,the solute is water itself. Mass of water = $64

Vedclass · Accepted Answer

$55.5$

Vedclass · Answer

(B) Molality $(m)$ is defined as the number of moles of solute per kilogram of solvent. For pure water,the solute is water itself. Mass of water = $648 \ g = 0.648 \ kg$. Molar mass of water $(H_2O)$ = $(2 	imes 1) + 16 = 18 \ g/mol$. Moles of water = $\frac{	ext{Mass}}{	ext{Molar mass}} = \frac{648 \ g}{18 \ g/mol} = 36 \ mol$. Molality $(m)$ = $\frac{	ext{moles of solute}}{	ext{mass of solvent in kg}} = \frac{36 \ mol}{0.648 \ kg} \approx 55.55 \ m$. However,in the context of pure water,the molality is often calculated as $\frac{1000 \ g}{18 \ g/mol 	imes 1 \ kg} = 55.5 \ m$.

The molality of $648 \ g$ of pure water is .................. $m$.

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