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Friday, July 5, 2019

Percent Composition continued

Here is a more complicated example:

What is the percent composition of calcium acetate? To solve this, we must first write the formula for calcium acetate. If you need a refresher on writing formulas, you can go back to nomenclature. 

Calcium acetate is Ca(C2H3O2)2

So, the question is really asking what are the percentages of Ca, C, H and O.

To solve this we set up the fractions below:




If you aren’t sure why we used 4 times the molar mass of C (and 6 of H and 4 of O) take a look at the formula. Each molecule of calcium acetate contains 2 acetate ions and each acetate ion contains 2 carbons. So 2x2=4 C atoms per molecule of calcium acetate.

Substituting in the values for the variables above, gives:



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