Question

A hydrocarbon has an empirical formula of `CH_2`, and a molecular mass of `42*g*mol^-1`. What is the hydrocarbon?

Answer 1

Well we got propylene or cyclopropane.....i.e. `C_3H_6`....

Explanation:

The molecular formula is always a whole number multiple of the empirical formula....

And thus ...........

`underbrace(12.01*g*mol^-1+2xx1.01*g*mol^-1)_"empirical formula"xxn=underbrace(42*g*mol^-1)_"molecular mass"`

And so `n=(42.0*g*mol^-1)/(12.01*g*mol^-1+2xx1.01*g*mol^-1)=3`

And so the molecular formula is `3xxCH_2-=C_3H_6`....and this is either propylene, `H_3C-CH=CH_2` or `"cyclopropane"`.