Question

A sample in the lab is found to contain 0.450 g magnesium and 2.95 g bromine. what is the empirical formula of the sample?

Answer 1

We need to find the number of moles that each of the given substances. The molar mass of magnesium is 24.3 g/mol and Bromine has a molar mass of 79.90 g/mol. From the given mass of each species, the moles of Mg and Br are 0.018 and 0.369 respectively. There are 2 Br in one Mg. The sample is MgBr2. 

Answer 2

Answer:

$MgBr_2$ is the empirical formula of the sample.

Explanation:

Mass of magnesium = 450 g

Moles of magnesium  =$\frac{450 g}{24 g/mol}=0.01875 mol$

Mass of bromine = 2.95 g

Moles of bromine =$\frac{2.95 g}{80 g/mol}=0.03687 mol$

In order to determine the empirical formula we will divide all the moles of each element with the smallest value of moles.

For magnesium :

$\frac{0.01875 mol}{0.03687 mol}=0.5085\approx 0.5$

For bromine :

$\frac{0.03687 mol}{0.03687 mol} =1$

The empirical formula of the sample:

$Mg_{0.5}Br_1=Mg_{\frac{1}{2}}Br_1=MgBr_2$

$MgBr_2$ is the empirical formula of the sample.