Question

The empirical formula for a compound that contains 5.11 grams phosphorus, and 39.55 grams bromine is

Answer 1

First, we have to find the number of moles of each element. The molar mass of phosphorus is 31 g/mol and the molar mass of bromine is 80 g/mol (You can find this in the periodic table):

`5.11\text{ g P}\cdot\frac{\text{1 mol P}}{31\text{ g P}}=0.165\text{ moles P.}`
`39.55\text{ g Br}\cdot\frac{1\text{ mol Br}}{80\text{ g Br}}=0.494\text{ moles Br.}`

And then, we have to divide each value by the least value obtained. In this case, we have to divide everything by 0.165:

`\begin{gathered} 0.165\text{ moles P/0.165=1 mol P.} \\ 0.494\text{ moles Br/0.165=2.99 moles Br}\approx3\text{ moles Br.} \end{gathered}`

We're going to have 1 mol of phosphorus and 3 moles of bromine obtaining the empirical formula PBr3.