Question

The empirical formula of a compound is `CH`. If the molar mass of this compound is about 78 g, what is its molecular formula?

Answer 1

`C_6H_6`

Explanation:

The `"empirical formula"` is the simplest whole number ration that defines constituent atoms in a species. The `"molecular formula"` is always a multiple of the `"empirical formula"`.

Given the above: `"molecular formula" =nxx("empirical formula")`

Thus `"molecular formula" = 78.0*g*mol^-1 = n(12.011+1.00794)*g*mol^-1`

`n=78/(12.011+1.00794)` `=` `6`.

And `"molecular formula"= C_6H_6`

Sometimes (but not here!) `"molecular formula"` `-=` `"empirical formula"`, i.e. the mulitple `n` `=` `1`.