Mole Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Mole.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A counting unit for atoms and molecules, equal to 6.022 \times 10^{23} particles (atoms, molecules, or ions).

A 'chemist's dozen'—a huge number that makes atom-counting practical.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: The mole links the atomic scale (particles) to the lab scale (grams).

Common stuck point: One mole of different substances has different masses but the same number of particles.

Worked Examples

Example 1

easy
What is a mole and why is it useful in chemistry?

Solution

  1. 1
    A mole is a counting unit: 1\,\text{mol} = 6.022 \times 10^{23} particles (Avogadro's number).
  2. 2
    It bridges the atomic scale (individual atoms/molecules) and the macroscopic scale (grams, liters).
  3. 3
    One mole of any element has a mass in grams equal to its atomic mass in amu.

Answer

1\,\text{mol} = 6.022 \times 10^{23}\text{ particles}
The mole is the chemist's counting unit, analogous to a 'dozen' but for atoms and molecules. It allows us to relate masses we can measure to numbers of particles.

Example 2

medium
How many moles of water are in 36.0 g of \text{H}_2\text{O}? (Molar mass of \text{H}_2\text{O} = 18.0\,\text{g/mol})

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
How many moles are in 40.0 g of NaOH? (Molar mass = 40.0\,\text{g/mol})

Example 2

easy
A sample contains 1.204 \times 10^{24} molecules of ammonia. How many moles of \text{NH}_3 is this?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

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