When 5.6 grams of NaCl are dissolved in enough water to create a 125-gram solution, what is the solution's concentration, expressed as a percent by mass?

Percent by mass is another way of expressing concentration in mixtures. It would be mass of a substance per mass of the mixture times 100 percent. We calculate as follows:

Percent by mass NaCl = 5.6 g / 125 g x 100 = 4.48%

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