Using Mass Percent in Calculations

We can use the mass percent of a solution as a conversion factor between mass of the solute and mass of tire solution. The key to using mass percent in this way is to write it as a fraction. 

A solution containing 3.5% sodium chloride, for example, has the following conversion factor. 

This conversion factor converts from grams of solution to grams of NaCl. If you want to go the other way, simply invert the conversion factor. 

For example, to use mass percent as a conversion factor, consider a water sample from the bottom of Lake Nyos containing 8.5% carbon dioxide by mass. We can determine how much carbon dioxide in grams is contained in 28.6 L of the water solution. (Assume that the density of the solution is 1.03 g/mL.) We begin by sorting the information in the problem statement. 

We strategize by drawing a solution map that begins with L solution and shows the conversion to mL solution and then to g solution using the density. Then we proceed from g solution to g CO2, using the mass percent (expressed as a fraction) as a conversion factor. 

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