Question

What is the quantity of water that should be added to $16$ g methanol to make the mole fraction of methanol as $0.25$?

• A. 27 gm
• B. 12 gm
• C. 18 gm
• D. 36 gm

Answer 1

The correct option is A 27 gm

The ratio of the mole fraction of water to mole fraction of methanol is $\frac{X_{H_{2}O}}{X_{C{H}_{2}OH}}=\frac{0.75}{0.25}=3$
The number of moles of methanol, $n_{C{H}_{3}OH}=\frac{16}{32}=0.5$
The number of moles of water, $n_{H_{2}O}=3\times 0.5=1.5$.
Weight of water, $m_{H_{2}O}=1.5\times 18=27g$.