It is often necessary to convert from moles of a substance to mass in grams or vice versa.Such conversion are readily made by using general relation

m = MM x n

where m is the mass in grams ,MM is the molar mass (g/mol) and n the amount is moles.In fact molar mass MM is the conversion factor that allows you to calculate n from m and vice versa.

For example:You have 0.0654 mol of ZnI2 , how many grams of zince iodide in this?

solution; molar mass of ZnI2 = 319 g/mol,so we write

1mole of ZnI2 = 319 g ZnI2

conversion factor:

319g ZnI2/1 mole ZnI2 or 1mole ZnI2/319 g ZnI2

Note the unit that you are converting from should be your bottom of conversion factor and unit you are converting to should be on the top.

so you should conversion factor 319g ZnI2/1 mole ZnI2

0.0654 mol ZnI2 x 319g ZnI2/1 mole ZnI2 = 20.9 g ZnI2