Question

Compound Y is a hydrocarbon that contains 85.7% carbon by mass. The diagram shows mass spectrum of compound Y Determine molecular formula of Y?

Answer 1

I gets...`C_6H_12` as the molecular formula....

Explanation:

We know that the hydrocarbon is `85.7%` by mass carbon. And so we address the empirical formula by assuming an `100*g` mass of the unknown compound...

`"Moles of carbon"=(85.7*g)/(12.01*g*mol^-1)=7.14*mol`

`"Moles of carbon"=(14.3*g)/(1.00794*g*mol^-1)=14.2*mol`..

Now clearly the empirical formula is `C_((7.14*mol)/(7.14*mol))H_((14.2*mol)/(7.14*mol))-=CH_2`

But the molecular formula is a whole number of the empirical formula....and this is....

`(CH_2)_n=84*g*mol^-1=nxx(12.011+2xx1.00794)*g*mol^-1`...

`n=(84*g*mol^-1)/(14*g*mol^-1)=6`...

And so our molecular formula is `6xxCH_2=C_6H_12`...

Good question!