Moles & Molar MassHESI A2 cheat sheet

Counting by weighing

9 key facts 5 practice questions Reviewed Oct 2026

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The Mole

1 mole = 6.022 × 10²³ particles (Avogadro's number)
A counting unit, like a dozen

Molar Mass

The mass of one mole, in grams per mole
Read it off the periodic table and add up the atoms
H₂O = 2(1.0) + 16.0 = 18 g/mol

Conversions

grams → moles: divide by molar mass
moles → grams: multiply by molar mass
moles → particles: multiply by 6.022 × 10²³

Method

Use dimensional analysis so the units cancel

Key takeaway

Counting by weighing

Before you read

Test yourself first: 5 questions

Question 1 of 5

To measure the mass of a small rock, the best tool is a:

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