To calculate the molar mass of a formula (also known as

relative formula mass, or M

_{r}), simply add together the A

_{r} (

relative atomic mass) of all the elements in that formula.

**One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass of that substance.**

So, the molar mass of MgCl_{2} is -

A_{r} of Mg = 24

A_{r} of Cl = 35.5. * 2 because there are two Cl.

24 + (35.5 * 2 ) = 95. So the molar mass of MgCl_{2} is simply 95.