Question

A hydrocarbon has `80%` carbon content. What is its empirical formula?

Answer 1

If the hydrocarbon has 80% carbon content, then the empirical formula is `CH_3`.

Explanation:

We assume a mass of `100*g` of stuff...

`"Moles of carbon"=(80.0*g)/(12.011*g*mol^-1)=6.67*mol.`

`"Moles of hydrogen"=(20.0*g)/(1.00794*g*mol^-1)=19.84*mol.`

We divide thru by the smallest quantity, i.e.

`C:(6.67*mol)/(6.67*mol)=1`

`H:(19.84*mol)/(6.67*mol)=3`

So our empirical formula is `CH_3`. In fact, this is consistent with a molecular formula of `C_2H_6`, i.e. `"ethane"`. The question might have asked this, had they quoted a proper value for molecular weight.