An unknown compound has a percent composition of 52.10% potassium, 15.8% carbon, and 32.1% oxygen. The molar mass of the compound is 150.22 g/mol. What is the empirical formula and the molecular formula of this compound?

1 Answer
Jun 29, 2016

The empirical formula is C_2K_2O_3

Explanation:

As is typical with these questions, we assume 100*g of unknown compound, and work out the MOLAR quantities of each element present:

" moles of C": (15.8*g)/(12.011*g*mol^-1)=1.32*mol

" moles of K": (52.8*g)/(39.10*g*mol^-1)=1.35*mol

" moles of O": (32.1*g)/(15.999*g*mol^-1)=2.00*mol

Now if we divide thru by the lowest molar quantity, we get CKO_(1.5); if we multiply this preiminary formula by 2 we get whole numbers:

C_2K_2O_3 is the empirical formula.

But "(empirical formula)"xxn = "molecular formula"

Thus, solving for n:

150.22*g*mol^-1=nxx(2xx12.011+2xx39.1+3xx15.999)*g*mol^-1

Clearly, n=1, and the molecular formula is C_2O_3K_2

This corresponds to no reasonable formula I know; C_2O_4K_2 would be reasonable. It is possible that you have been given duff values.