Question

An organic compound with a vapour density of 45 was found to contain 54.5% carbon and 9.1% hydrogen calculate the molecular formula of the compound?

Answer 1

Well we gots `C_4H_8O_2`...

Explanation:

We assume a mass of `100*g` of compound...and thus...

`"Moles of carbon"-=(54.5*g)/(12.011*g*mol^-1)=4.54*mol.`

`"Moles of hydrogen"-=(9.1*g)/(1.00794*g*mol^-1)=9.03*mol.`

`"Moles of oxygen"-=(100*g-54.5*g-9.1*g)/(16.00*g*mol^-1)=2.28*mol.`

Note that it is typical to assume that the missing percentage is due to oxygen, because there are few ways to determine percentage oxygen....

And we divide thru by the smallest molar quantity to get an empirical formula of....

`C_((4.54*mol)/(2.28*mol))H_((9.03*mol)/(2.28*mol))O_((2.28*mol)/(2.28*mol))-=C_2H_4O`...

Now we are given the vapour density of this material as `45`..and this is relative to dihydrogen gas....and thus the molecular mass of the compound is `90*g*mol^-1`...

The `"molecular formula"-=C_4H_8O_2`...this question seems a bit suspect....so check the source...