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

1 Answer
Dec 30, 2015

Empirical formula: #"CaCO"_3#


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#


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.