Question

Calculate the molarity and molality of 20 percent aqueous ethanol solutions by volume (density of the solutions=0.960

Answer 1

$\fbox{\texttt{\green{Answer:}}}$

A. Molarity = 3.48 M

B. Molality = 4.35 m

$\fbox{\texttt{\pink{Given:}}}$

20% $\bold{C_2H_5OH}$ by volume means that 20 mL of $\bold{C_2H_5OH}$ is dissolved in 100 mL of solution.

Density of solution = 0.96 g/mL

$\fbox{\texttt{\blue{To\:find:}}}$

A. Molarity

B. Molality

$\fbox{\texttt{\red{How\:to\:Find:}}}$

Weight of solution = 100 × 0.96 = 96 g

Volume of water = 100 - 20 = 80 mL

Weight of water (in the solution) = 80 g

$\therefore$Weight of $\bold{C_2H_5OH}$ = 96 - 80 = 16 g

Molecular weight of $\bold{C_2H_5OH}$ = 12 × 2 + 5 + 16 + 1 = 46 g/mol

$\hrulefill$

$\bold{A.\:Molarity:-}$

$\bold{\frac{W_2\times{}1000}{M_{w2}\times{}Vol_{sol}}=}$

$\bold{\frac{16\times{}1000}{46\times{}100}=3.48\:M}$

$\bold{B.\:Molality:-}$

$\bold{\frac{W_2\times{}1000}{M_{w2}\times{}W_{1}}=}$

$\bold{\frac{16\times{}1000}{46\times{}80}=4.35\:m}$