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Chemistry · Grades 9–12

Mass to amount in moles

Divide mass by molar mass. Grams cancel with g/mol to leave moles; do not confuse mass with amount of substance.

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Rule and assumptions

Divide mass by molar mass. Grams cancel with g/mol to leave moles; do not confuse mass with amount of substance.

n = m/M

Worked examples

A model sample has mass 51 g and stated molar mass 121 g/mol. Find its amount. Round to 3 decimal places if needed. Answer in mol.

n = m/M 51/121 = 0.421

0.421 mol

A model sample has mass 7 g and stated molar mass 126 g/mol. Find its amount. Round to 3 decimal places if needed. Answer in mol.

n = m/M 7/126 = 0.056

0.056 mol

Try two questions

  1. A model sample has mass 44 g and stated molar mass 123 g/mol. Find its amount. Round to 3 decimal places if needed. Answer in mol.

  2. A model sample has mass 131 g and stated molar mass 24 g/mol. Find its amount. Round to 3 decimal places if needed. Answer in mol.

Answers and reasoning

Answers and marking notes
  1. 0.358 mol

    n = m/M 44/123 = 0.358

  2. 5.458 mol

    n = m/M 131/24 = 5.458

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.