Question

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

Answer 1

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.