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Concentration of solutions: units, practice, pitfalls

Quantitative chemistry • Concentration of solutions

Key concepts

What you'll likely be quizzed about

  • Concentration measures the amount of solute per volume of solution.
  • The primary formula uses amount in moles (n) and volume in cubic decimetres (V): c = n / V.
  • Incorrect volume units lead to systematic errors because the formula requires volume in dm³ when reporting concentration in mol dm-3.

Flashcards

Test your knowledge with interactive flashcards

Calculate moles in 18.0 g of H₂O (Mr = 18.0).

Click to reveal answer

n = mass / Mr = 18.0 / 18.0 = 1.00 mol.

Key notes

Important points to keep in mind

Convert volume to dm³ when using c = n / V for mol dm-3.

Divide cm³ by 1000 to obtain dm³; multiply dm³ by 1000 to obtain cm³.

Use mass divided by Mr to convert grams to moles; ensure mass units match Mr units (grams).

Use the final solution volume after dilution, not the volume of solvent added.

Show units at every step; unit cancellation reveals incorrect substitutions.

Round only the final answer to required significant figures; keep extra figures in intermediate steps.

Check whether the required concentration is molar (mol dm-3) or mass-based (g dm-3) before converting.

Review algebra when rearranging formulas; isolate the intended variable before substituting numbers.

Label volumes clearly as cm³ or dm³ to avoid factor-of-1000 errors.

When presented with titration data, use titres as volumes and ensure both solutions use the same volume unit.

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