# How many formula units make up 39.8 g of magnesium chloride?

Dec 26, 2016

There are 2.52 × 10^23 formula units in 39.8 g of magnesium chloride.

#### Explanation:

The formula of magnesium chloride is $\text{MgCl"_2}$.

The molar mass of $\text{MgCl"_2}$ is $\text{(24.30 + 2 × 35.45) g/mol" = "95.20 g/mol}$.

${\text{Moles of MgCl"_2 = 39.8 color(red)(cancel(color(black)("g MgCl"_2))) × ("1 mol MgCl"_2)/(95.20 color(red)(cancel(color(black)("g MgCl"_2)))) = "0.4181 mol MgCl}}_{2}$

There are 6.022 × 10^23 formula units in 1 mol, so

${\text{Formula units" = 0.4181 color(red)(cancel(color(black)("mol MgCl"_2))) × (6.022 × 10^23color(white)(l) "formula units MgCl"_2)/(1 color(red)(cancel(color(black)("mol MgCl"_2)))) = 2.52 × 10^23color(white)(l) "formula units MgCl}}_{2}$