Question

You are asked to prepare a solution that is 2% by weight ethanol in water. Note that the molecular weight of ethanol is 46.07 g/mol and water is 18.02 g/mol. What is the molality of ethanol in this solution?

Answer 1

Answer:

0.4429 m

Explanation:

Given that mass % of the ethanol in water = 2%

This means that 2 g of ethanol present in 100 g of ethanol solution.

Molality is defined as the moles of the solute present in 1 kilogram of the solvent.

Given that:

Mass of $CH_3CH_2OH$ = 2 g

Molar mass of $CH_3CH_2OH$ = 46.07 g/mol

The formula for the calculation of moles is shown below:

$moles = \frac{Mass\ taken}{Molar\ mass}$

Thus,

$Moles= \frac{2\ g}{46.07\ g/mol}$

$Moles\ of\ CH_3CH_2OH= 0.0434\ moles$

Mass of water = 100 - 2  g = 98 g = 0.098 kg ( 1 g = 0.001 kg )

So, molality is:

$m=\frac {0.0434\ moles}{0.098\ kg}$

Molality = 0.4429 m