Example 3.14: Calculating Molar Concentrations

A 355-mL soft drink sample contains 0.133 mol of sucrose (table sugar). What is the concentration of sucrose in the beverage?

Solution

\(V_{\mathrm{solution}}\) \(= 355.\ \mathrm{mL}\)


\(n_{\mathrm{sucrose}}\) \(= 0.133\ \mathrm{mol}\)


Since the chemical amount of solute and the volume of solution are both given, the concentration can be calculated using its definition.

\(c_{\mathrm{sucrose}}\) \(= \dfrac{n_{\mathrm{sucrose}}}{V_{\mathrm{solution}}}\)

\(\ \ \ =\dfrac{0.133\ \mathrm{mol}}{355.\ \mathrm{mL}}\)

\(\ \ \ =3.75\times 10^{-4}\ \frac{\mathrm{mol}}{\mathrm{mL}}\)


If we want to switch to the more common units mol/L, or short M:
\(c_{\mathrm{sucrose}}\) \(= 3.75\times 10^{-4}\ \frac{\mathrm{mol}}{\mathrm{mL}}\)

\(\ \ \ =0.375\ \mathrm{M}\)