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How to convert moles into mass (grams)?

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How to convert moles into mass?

To convert moles into mass, we first need to find the molar mass of the compound given. This can be done by looking at the mass of each element in the periodic table and then multiplying each mass by the number of atoms of that element in the compound. Molar mass has the units grams/mol which allows to convert between moles and grams.

To go from moles to grams, we need to multiply the number of moles by the molar mass. Let's look at the units: moles * grams/mols = moles will cancel giving us grams only.

Let's now look at an example

Example: What is the mass, in grams, of 1.223 mol of iron(III) sulfate?


iron(III) sulfate has the formula Fe2(SO3)3 ( when writing formulas for ionic compounds we switch the oxidation numbers).

In order for us to calculate mass, we need to determine the molecular mass of iron(III) sulfate first by looking at the Period Table. Lets also keep in mind that Fe2(SO3)3 has 2 atoms of iron, 3 atoms of sulfur, and 9 atoms of oxygen.

Fe = 2* 55.845 g/mol= 111.69

S = 3* 32.06 g/mol= 96.18

O= 9* 15.999g/mol= 143.991

143.991 + 96.18 + 111.69 = 351.861g/mol (Molas Mass)

1.223 mol * 351.861g/mol = 430.326003 grams.

Using the correct number of significant figures, since there are 4 sig figs in 1.223, our answer should have 4 sig figs, thus becoming 430.3 grams.

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