Question

A large family of boron-hydrogen compounds has the general formula BxHy . One member of this family contains 88.5% B ;the remainder is hydrogen. What is its empirical formula?

Answer 1

Well, we got the empirical formula `BH_2`

Explanation:

We are given that the stuff contains `85%` boron by mass... (well we assumed it was by mass, but this is the standard scenario).

And so we ASSUME a `100*g` mass of the borane.....and we interrogate the empirical formula....

`"Moles of boron"=(85*g)/(10.81*g*mol^-1)=7.86*mol.`

`"Moles of hydrogen"=(15*g)/(1.00794*g*mol^-1)=14.882*mol.`

We divide thru by the SMALLER molar quantity, that of boron, to get the empirical formula, which is the simplest whole number ratio representing constituent atoms in a species...

And so we got `B_((7.86*mol)/(7.86*mol))H_((14.882*mol)/(7.86*mol))-=BH_2`...and there are several known borane hydrides with this empirical formula....