A hydrogen ion is just a proton. So an acid is anything that gives away protons and a base is anything that takes them. How completely an acid gives them away decides whether it is strong or weak, which is not the same as concentrated or dilute. Extended content.
Extended. An acid is a proton donor and a base is a proton acceptor, because an H+ ion is a proton. A strong acid is completely dissociated in water: HCl(aq) → H+(aq) + Cl−(aq). A weak acid is only partially dissociated: CH3COOH(aq) ⇌ H+(aq) + CH3COO−(aq). At the same concentration a weak acid has fewer H+ ions, a higher pH and reacts more slowly.
Extended content. A hydrogen atom that loses its electron leaves just a proton, so H+ and "proton" mean the same thing.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
(Extended) An acid is defined as:
(Extended) A weak acid is one that:
(Extended) In NH3 + H+ → NH4+, ammonia acts as:
(Extended) Which of these is a strong acid?
Compare hydrochloric acid and ethanoic acid of the same concentration in the simulator. Look at the pH and at how many molecules have split into ions.
| Same concentration, 0.1 mol/dm3 | Hydrochloric acid (strong) | Ethanoic acid (weak) |
|---|---|---|
| dissociation | complete | partial |
| H+ concentration | high | low |
| pH | about 1 | about 3 |
| with magnesium | vigorous fizzing | slow fizzing |
| electrical conductivity | good | poor |
Other strong acids: sulfuric and nitric acid. Other weak acids: citric acid and carbonic acid. With enough time, the same amount of each acid still produces the same total amount of hydrogen with excess magnesium, because the weak acid keeps dissociating as its H+ ions are used up.
Strong and concentrated are different ideas. Strength is about how completely the acid dissociates; concentration is about how much acid is dissolved per dm3. A dilute solution of a strong acid and a concentrated solution of a weak acid are both possible.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
(Extended) Hydrochloric acid and ethanoic acid of the same concentration are compared. Which statement is correct?
(Extended) Which equation shows ethanoic acid acting as a weak acid in water?
(Extended) Equal volumes of 0.1 mol/dm3 hydrochloric acid and 0.1 mol/dm3 ethanoic acid react with excess magnesium ribbon. What is observed?
(Extended) Which statement correctly distinguishes a concentrated weak acid from a dilute strong acid?
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