Question

a solution of ethanol (c₂h₅oh) in water is prepared by dissolving 50.0 ml of ethanol (density = 0.79 g/cm³) in enough water to make 250.0 ml of solution. what is the molarity of the solution? molarity = m

Explanation:

Step1: Calculate the mass of ethanol

Use the formula \(m=
ho V\). Given \(
ho = 0.79\ \text{g/cm}^3\) and \(V = 50.0\ \text{mL}=50.0\ \text{cm}^3\).
\(m=(0.79\ \text{g/cm}^3)\times(50.0\ \text{cm}^3) = 39.5\ \text{g}\)

Step2: Calculate the molar mass of ethanol \((C_2H_5OH)\)

The molar mass of \(C = 12.01\ \text{g/mol}\), \(H = 1.008\ \text{g/mol}\), \(O=16.00\ \text{g/mol}\).
\(M = 2\times12.01+6\times1.008 + 16.00=46.07\ \text{g/mol}\)

Step3: Calculate the number of moles of ethanol

Use the formula \(n=\frac{m}{M}\).
\(n=\frac{39.5\ \text{g}}{46.07\ \text{g/mol}}\approx0.857\ \text{mol}\)

Step4: Calculate the molarity of the solution

Use the formula \(M=\frac{n}{V}\) (where \(V\) is in liters). Given \(V = 250.0\ \text{mL}=0.2500\ \text{L}\).
\(M=\frac{0.857\ \text{mol}}{0.2500\ \text{L}} = 3.43\ \text{M}\)

Answer:

\(3.43\)