General chemistryLesson 1 of 1 in the course Composition of Substances and Solutions

Formula Mass, Molar Mass, and Mole-to-Particle Conversions

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Formula mass connects a substance’s chemical formula to the mass contributed by its atoms. In this lesson, you will learn how to calculate formula mass and distinguish molecular mass from the formula mass of an ionic compound.

The formula mass of a substance is the sum of the average atomic masses of all atoms represented in its chemical formula. It is reported in atomic mass units, abbreviated amu. A subscript indicates how many atoms of the preceding element are included; a missing subscript means one atom.

All flashcards

What is formula mass?
The total of the average atomic masses of all atoms represented in a substance’s formula, expressed in amu.
What is a mole?
An amount of substance containing exactly 6.02214076 × 10²³ specified entities.
What is molar mass?
The mass of one mole of a substance, expressed in grams per mole.
How do you convert sample mass to moles?
Divide the sample mass in grams by the substance’s molar mass in grams per mole.
How do you convert moles to particles?
Multiply the amount in moles by Avogadro’s number, identifying the particle type.

Quiz questions

  1. What does the formula mass of a substance represent?Answer: The sum of the average atomic masses of all atoms represented in its chemical formula.
  2. How many oxygen atoms are represented by the formula Al2(SO4)3\mathrm{Al_2(SO_4)_3}?Answer: 12 oxygen atoms.
  3. Why may the formula mass of a covalent compound also be called its molecular mass?Answer: Because its formula represents the atoms in a single molecule.
  4. Why is molecular mass usually not the best term for an ionic compound such as NaCl?Answer: Its formula represents an ion ratio in the solid, not a discrete molecule.
  5. What is the approximate formula mass of Ca3(PO4)2\mathrm{Ca_3(PO_4)_2} using Ca = 40.08, P = 30.97, and O = 16.00 amu?Answer: 310.18 amu.

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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