Question

A solution contains $36$% water and $64$% acetaldehyde by mass. Mole fraction of acetaldehyde is:

• A. 0.42
• B. 0.2
• C. 4.2
• D. 2.1

Answer 1

The correct option is A 0.42

Let us assume the mass of solution $=100gm$.

Mass of water $=36gm$

Mass of acetaldehyde, $C{H}_{2}O$ $=64gm$

Molar mass of acetaldehyde $=44gm$

Mole fraction of acetaldehyde $=\frac{\text{moles of acetaldehyde}}{\text{moles of acetaldehyde + moles of water}}$

Mole fraction of acetaldehyde $=\frac{\left(64/44\right)}{(64/44+36/18)}=\frac{1.45}{(1.45+2)}=\frac{1.45}{3.45}=0.42$