Question

Explain how you would make up a one molar (1m) solution of ethyl alcohol.

Answer 1

The formula of molarity is:

$molarity = \frac{number of moles of solute}{volume of solution in Liter}$

Number of moles is given as:

$number of moles of solute= \frac{mass of solute}{Molar mass of solute}$

So, the formula of molarity can be written as:

$molarity = \frac{\frac{mass of solute}{Molar mass of solute}}{volume of solution in Liter}$    -(1)

Molar mass of ethyl alcohol, $C_2H_5OH$ = $2\times 12+6\times 1+16 = 46 g/mol$

Molarity of ethyl alcohol, $C_2H_5OH$ = 1 molar  (given)

Let the volume of solvent that is water be 1 L.

Substituting the values in formula (1):

$1 M = \frac{\frac{mass of solute}{46 g/mol}}{1 L}$

$mass of solute = 46 g/mol\times 1 mol/L\times 1 L$

$mass of solute = 46 g$

Since, ethyl alcohol is liquid in room temperature:

Density of ethyl alcohol is $0.7892 g/mL$

Density = $\frac{mass}{volume}$

So, volume of ethyl alcohol = $\frac{mass of ethyl alcohol}{density of ethyl alcohol}$

Volume of ethyl alcohol = $\frac{46 g}{0.7892 g/mL}$

Volume of ethyl alcohol = $58.29 mL$

Hence, by dissolving 58.29 mL of ethyl alcohol in 1 L of water, 1 M solution of ethyl alcohol can be prepared.