Avogadro's Number Chemistry Example 3

Follow the full solution, then compare it with the other examples linked below.

Example 3

medium
How many molecules are in 2.5 moles of water (H2O\text{H}_2\text{O})? How many individual atoms is that?

Solution

  1. 1
    Step 1: Find the number of molecules: N=2.5×6.022×1023=1.506×1024N = 2.5 \times 6.022 \times 10^{23} = 1.506 \times 10^{24} molecules.
  2. 2
    Step 2: Each H2O\text{H}_2\text{O} molecule contains 3 atoms (2 hydrogen + 1 oxygen).
  3. 3
    Step 3: Total atoms =3×1.506×1024=4.517×1024= 3 \times 1.506 \times 10^{24} = 4.517 \times 10^{24} atoms.

Answer

1.506×10241.506 \times 10^{24} molecules; 4.517×10244.517 \times 10^{24} atoms
Avogadro's number (6.022×10236.022 \times 10^{23}) converts moles to individual particles. To count total atoms in a molecular substance, first find the number of molecules, then multiply by the number of atoms per molecule. Water has 3 atoms per molecule (2 H + 1 O), so the atom count is three times the molecule count.

About Avogadro's Number

The defined number of particles in exactly one mole of any substance: 6.022×10236.022 \times 10^{23}.

Learn more about Avogadro's Number →

More Avogadro's Number Examples

Example 1 easy

How many molecules are in [formula] mol of [formula]?

Example 2 medium

How many individual oxygen atoms are in [formula] mol of [formula]?

Example 4 easy

How many atoms are in [formula] mol of iron (Fe)?

Example 5 medium

How many chloride ions are in [formula] mol of [formula]?

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Related Concepts

MoleMolar Mass