A compound contains 40% calcium, 12% carbon, and 48% oxygen by mass. What is the empirical formula of this compound?

1 Answer
Owen Bell
Dec 30, 2015

Empirical formula: "CaCO"_3

Explanation:

Although you have not been provided with direct masses, you can use the percentage composition values in place of masses.

First, calculate the number of moles of each element:

["mol"("Ca") = 40/40 = 1]["mol"("C") = 12/12 = 1]["mol"("0") = 48/16 = 3]

Your next step would be to divide by the smallest value, but since this is 1 this would have no effect on the ratios already present. Thus, the empirical formula of the compound would be:

" Ca ":" C ":" O "
" "1" ":" "1" ":" "3

"CaCO"_3

This is the formula for the ionic compound calcium carbonate, confirming that our result is indeed in the magnitude of a plausible answer. In fact, given the fact that calcium carbonate is ionic, it is also true that this empirical formula equates to the unit formula of the compound.

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