How to convert grams to moles

The calculation of the molecular mass of KMnO4 would be:

Molecular mass KMnO ₄ = (39.0983 + 54.9380 + 4 15.9999) = 158.0359 g/mol

Calculation of the number of moles

Once the atomic or molecular mass is known, the formula to convert grams to moles would be:

n = m / atomic or molecular mass

Where n = number of moles, and m = the mass expressed in grams.

Examples of calculating the number of moles from grams

Example 1. How many moles would be 25 grams of KMnO ₄ ?

The molecular mass of the compound, as calculated above as an example is 158.0359 g/mol.

n = m / atomic or molecular mass

n = 25 g / 158.0359 g/mol = 0.1582 mol

Example 2. Calculate the moles in 100 g of KClO ₄ .

To calculate the molecular mass of the compound, first find out the atomic masses of the elements that are part of the compound.

• Atomic mass of potassium, K = 39.0983
• Atomic mass of chlorine, Cl = 35.453
• Atomic mass of oxygen, O = 15.9999
• Molecular mass KClO ₄ = (39.0983 + 35.453 + 4 15.9999) = 138.547 g/mol

n = m / atomic or molecular mass

n = 100 g / 138.547 g/mol = 0.722 mol

Example 3. Calculate the moles found in 5.00 g of cobalt (II) sulfate hexahydrate (CoSO ₄ · 6H ₂ O).

• Atomic mass of cobalt, Co = 58.9332
• Atomic mass of sulfur, S = 32.065
• Atomic mass of oxygen, O = 15.9999
• Atomic mass of hydrogen, H = 1.007

Molecular mass CoSO ₄ 6H ₂ O = 58.9332 + 32.065 + 4 15.9999 + 6 (2 1.007 + 15.9999) = 263.084 g/mol

n = m / atomic or molecular mass

n = 5.00 g / 138.547 g/mol = 0.722 mol

Sources

• ChemTeam: Grams to Moles. (2021). Retrieved 18 April 2021, from https://www.chemteam.info/Mole/Grams-to-Moles.html