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wise otter.Chemistry
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Acid-Base Chemistry

Topic 4 of 7

Strong and weak is different from concentrated and dilute

Separate extent of ionisation from amount per unit volume.

O-Level 6092 (2026) / SEC G3 K324 (2027)

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Pure only

Strong and weak is different from concentrated and dilute

Separate extent of ionisation from amount per unit volume.

A strong acid ionises essentially completely in water: HCl(aq) -> H+(aq) + Cl-(aq). A weak acid ionises only partly: CH3COOH(aq) reversibly forms H+(aq) and CH3COO-(aq). Many acid molecules remain un-ionised.

Concentration describes the amount of acid per unit volume, whether or not its molecules ionise. A strong acid can be dilute, and a weak acid can be concentrated. At the same concentration, comparing suitable monoprotic acids under the same conditions, the stronger acid produces more H+, usually gives a lower pH and reacts faster initially with magnesium.

Check your understandingDoes diluting hydrochloric acid turn it into a weak acid?Think it through, then reveal the answer
No. It reduces concentration, but hydrochloric acid is still classified as strong because the dissolved acid ionises essentially completely. Strength and concentration answer different questions.