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Molarity and concentration

Molarity = moles of solute ÷ litres of solution.

The common mistake

Using millilitres directly without converting to litres.

Instead: Convert volume to litres (÷ 1000), then divide moles by litres.

Worked example with Guide me

0.2 mol of salt is dissolved to make 500 mL. Find the molarity.

  1. Sugar · Volume in litres?
    Student · 0.5 L.
  2. Sugar · Moles ÷ litres?
    Student · 0.2 ÷ 0.5 = 0.4.

Answer: 0.4 mol/L (0.4 M)

Try 3 practice questions

  1. 1. 1 mol in 2 L?

    Show answer

    0.5 M

  2. 2. 0.1 mol in 250 mL?

    Show answer

    0.4 M

  3. 3. Moles in 2 L of 3 M solution?

    Show answer

    6 mol

Quick answers

What is the most common mistake with molarity and concentration?
Using millilitres directly without converting to litres.
How do I get molarity and concentration right?
Convert volume to litres (÷ 1000), then divide moles by litres.
Can you show a worked example?
0.2 mol of salt is dissolved to make 500 mL. Find the molarity. 0.4 mol/L (0.4 M)

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