Chemistry / Chem 0385 · Procedure · 60–90 seconds
Calculating Percent Composition from Experimental Mass Data
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Calculating percent composition from experimental data means dividing each element's measured mass by the sample's total mass, then converting each result to a percentage.
A sample known to contain only carbon, hydrogen, and nitrogen is analyzed and found to hold 7.34 g carbon, 1.85 g hydrogen, and 2.85 g nitrogen, for a total sample mass of 12.04 g. Dividing each element's mass by 12.04 g and multiplying by 100 gives about 60.9% carbon, 15.4% hydrogen, and 23.7% nitrogen. Checking that the three percentages sum to almost exactly 100% confirms no element's mass was left out of the total.
Forgetting to add every element's mass into the total before dividing produces percentages that do not sum to 100%, a mistake the summing check catches immediately.