Question

A sample in the lab is found to contain 0.45g magnesium and 1.5g bromine. What is the empirical formula of the sample?

Answer 1

The empirical formula is the formula in which we use the least subscripts for each atom in it.

We have magnesium and bromine

The their molar masses are:

`\begin{gathered} M_(Mg)=24.305g/mol \\ M_(Br)=79.904g/mol \end{gathered}`

So, the number of moles of each in the sample is:

`\begin{gathered} M_(Mg)=(m_(Mg))/(n_(Mg)) \\ n_(Mg)=(m_(Mg))/(M_(Mg))=(0.45g)/(24.305g/mol)=0.018514\ldots mol \\ \\ M_(Br)=(m_(Br))/(n_(Br)) \\ n_(Br)=(m_(Br))/(M_(Br))=(1.5g)/(79.904g/mol)=0.018772\ldots mol \end{gathered}`

Their ratio is:

`(n_(Mg))/(n_(Br))=(0.018514\ldots mol)/(0.018772\ldots mol)=0.9862\ldots\approx1`

That is, their ratio is about 1:1, thus, the empirical formula is MgBr.