Question

If the density of methanol is $0.793kg{L}^{-1}$, what volume of it is needed for making $2.5L$ of its $0.25M$ solution?

• A. 25.5 mL
• B. 52.5 mL
• C. 15.5 mL
• D. 10.5 mL

Answer 1

Answer: (A)

Molarity $=\frac{\text{Moles of}C{H}_{3}OH}{\text{Volume in}L}$
$\Rightarrow 0.25=\frac{\text{moles of }C{H}_{3}OH}{2.5}$
$\therefore$ Moles of $C{H}_{3}OH=2.5\times 0.25=0.625$
Mass of $C{H}_{3}OH=0.625\times 32=20g$
[Molar mass of $C{H}_{3}OH=12+1\times 3+16+1=32]$
$0.793\times 10^{3}g$ of $C{H}_{3}OH$ is present in $1000mL$.
$\therefore 20g$ of $C{H}_{3}OH$ is present in
$=\frac{1000}{0.793\times 10^3}\times 20=25.2mL$