How to Convert Mass Into Mole

Reviewed by Anne Schmidt

Last Updated: November 28, 2022 Fact Checked

Being able to calculate how many moles are in a certain amount of matter is an important skill in both inorganic and organics chemistry. In short, plug in any given values into the equation $n={\frac {m}{M}}$ and solve for $n$ .

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The equation you'll need to use is $n={\frac {m}{M}}$ , or the numbers of moles $n$ is equal to the mass $m$ divided by the molar mass $M$ . ^{[1]
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For example, if you have to calculate how many moles go into 74 g of hydrogen peroxide, you'll get $n={\frac {74g}{37{\frac {g}{mol}}}}$ , since you have 74 g of hydrogen peroxide, and the molar mass is 37 ${\frac {g}{mol}}$ . ^{[2]
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The unit grams is both in the numerator and denominator so that cancels out. Moles is in the denominator of the denominator, which leaves you with moles in the numerator. The final answer is $n={\frac {74}{37}}mol=2mol$ . ^{[3]
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How do I convert 8 grams of Hydrogen into moles?

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Number of moles = mass / molecular mass = 8 / 1 = 8, knowing that the molecular mass of hydrogen is one.

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Work out the units along with the problem. They are a good way to check your solution: if you end up with something like $g^{2}$ when you should end up with $mol$ , you know something went wrong along the way.

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