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

0.4429 m

Step-by-step 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 = (Mass\ taken)/(Molar\ mass)`

Thus,

`Moles= (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