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

`MgBr_2` is the empirical formula of the sample.

Step-by-step explanation:

Mass of magnesium = 450 g

Moles of magnesium =
`(450 g)/(24 g/mol)=0.01875 mol`

Mass of bromine = 2.95 g

Moles of bromine =
`(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 :

`(0.01875 mol)/(0.03687 mol)=0.5085\approx 0.5`

For bromine :

`(0.03687 mol)/(0.03687 mol) =1`

The empirical formula of the sample:

`Mg_(0.5)Br_1=Mg_{(1)/(2)}Br_1=MgBr_2`

`MgBr_2` is the empirical formula of the sample.