Question

The molality of a solution that is made by dissolving a certain mass of ethanol in 85.4 g of water is 0.950 m. How many moles of ethanol were dissolved?
0.0811 mol
0.0899 mol
11.1 mol
81.1 mol

Answer 1

Data:

m (molality) = 0.950 mol/Kg
moles of solute = ? (mol) = ?
mass of solvent = 85.4 g → 0.0854 Kg

Formula:

$m = \frac{moles\:of\:solute}{mass\:of\:solvent}$

Solving:

$m = \frac{moles\:of\:solute}{mass\:of\:solvent}$
$0.950\:mol/\diagup\!\!\!\!\!\!K\diagup\!\!\!\!\!\!g = \frac{moles\:of\:solute}{0.0854\:\diagup\!\!\!\!\!\!K\diagup\!\!\!\!\!\!g}$
$moles\:of\:solute = 0.950*0.0854$
$\boxed{\boxed{moles\:of\:solute = 0.08113 \approx 0.0811\:mol}}$ $\end{array}}\qquad\quad\checkmark$
Answer:
0.0811 mol