Mass percentage is one of the ways to express the concentration of a dissolved substance in a solution. Mass percentage refers to the ratio (expressed in percents) of a mass of a compound in the solution to the total mass of the solution. For instance, calculate the mass percent concentration for the solution obtained by dissolving 10 g of sodium chloride (NaCl) and 6 g of sodium bicarbonate (NaHCO3) in 120 g of water.

Add up the mass of all compounds in the solution, including the solvent, to calculate the total mass of the solution. In the example, the solution mass is equal to mass (NaCl) + mass (NaHCO3) + mass (water) = 10 g + 6 g + 120 g = 136 g.

Divide the mass of the first dissolved component by the solution mass, and then multiply the result by 100 to calculate the mass percentage. In our example, the first dissolved compound is NaCl; the mass percent is (10 g / 136 g) x 100 percent = 7.35 percent.

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Divide the mass of the second dissolved component by mass of the solution followed by multiplying by 100 to calculate the mass percentage. In this example, the second dissolved compound is NaHCO3, and its mass percentage is (6 g / 136 g) x 100 percent = 4.41 percent.