By Oxana Fox • Apr 29, 2023 12:10 am EST
Mass percentage expresses the concentration of a solute relative to the total mass of a solution. It is calculated as a percentage of the solute’s mass divided by the mass of the entire solution.
To determine the mass‑percent composition of a compound in a mixture, use:
Mass Percent = \(\frac{a}{M} \times 100\)where a is the mass of the solute and M is the total mass of the solution (solute + solvent).
Suppose 10 g of sodium chloride (NaCl) and 6 g of sodium bicarbonate (NaHCO₃) are dissolved in 120 g of water. The total solution mass is:
\(M = 10\text{ g} + 6\text{ g} + 120\text{ g} = 136\text{ g}\)
Mass percent of NaCl:
\(\frac{10\text{ g}}{136\text{ g}} \times 100\% = 7.35\%\)
Mass percent of NaHCO₃:
\(\frac{6\text{ g}}{136\text{ g}} \times 100\% = 4.41\%\)
Mass percent allows chemists to quantify the relative contributions of each component in a mixture, aiding in reaction design, quality control, and analytical calculations. For example, determining the elemental composition of glucose or the concentration of solutes in pharmaceutical formulations.
Molar mass, the mass of one mole of a substance, is related to mass percentage when converting between mass and mole quantities:
M = \(\frac{m}{n}\)
where M is the molar mass (kg mol⁻¹), m is the mass of the substance, and n is the number of moles.
A mole equals Avogadro’s number of atoms or molecules. While the number of particles is the same for any element, the mass differs because each atom has a distinct atomic weight.
