How many formula units make up 11.2 g of Magnesium Chloride MgCl2?

Solved:

Molar mass MgCl2 = 24.31 + 35.45 x 2 = 95.21g/mol

One mole is equal to 6.022*10^23 formula units

Each mole of MgCl2 has 6.022 x 10²³ MgCl2 molecules (formula units)

so number of formula units in the MgCl2 sample =

11.2 g MgCl2 * [1 mol / 95.21 g] x [6.022 x 10²³ formula units / mol]

= 7.0 x 10^22 MgCl2 formula units