Question

Mole fraction of ethanol and water mixture is $0.25$. Hence, percentage concentration of ethanol by weight of mixture is:

• A. $25\%$
• B. $75\%$
• C. $46\%$
• D. $54\%$

Answer 1

The correct option is C $46\%$

The mole fractions of ethanol and water are $0.25$ and $0.75$ respectively.

Let $1$ mol of the mixture be present.

The moles of ethanol and water will be $0.25$ and $0.75$ respectively.

The molar masses of ethanol and water are $46$ g/mol and $18$ g/mol respectively.

The masses of ethanol and water are $0.25\times 46=11.5$ g and $0.75\times 18=13.5$ g respectively.

The percentage concentration of ethanol by weight of mixture is $\frac{11.5}{11.5+13.5}\times 100=46$ %.

Hence, the correct option is $C$