An unknown compound was found to have a percent composition as follows 47.0% potassium, 14.5% carbon, and 38.5% oxygen. What is its empirical formula?

Md Ariful Islam

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In 100 g of compound there are 47.0 g potassium, 14.5 g carbon, and 38.5 g oxygen. Why?

We divide thru by the atomic masses:

$K$ $=$ $(47.0*g)/(39.1*g*mol^(-1))$ $=$ $1.20$.

$C$ $=$ $(14.5*g)/(12.0*g*mol^(-1))$ $=$ $1.21$.

$O$ $=$ $(38.5*g)/(16.0*g*mol^(-1))$ $=$ $2.4$.

Now if we divide thru by the lowest ratio, we get $K_nC_mO_o$ $=$ $KCO_2$ as the empirical formula.

You have likely got the dipotassium salt of oxalic acid, $HOC(=O)C(=O)OH$, which has precisely this empirical formula. I take it you are an undergraduate?

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