Electrolytes, Acids, Bases and Salts
What you must know
Apply Brønsted–Lowry and Lewis definitions. Know strong versus weak acids and bases, and the meaning of Ka, Kb, Kw and pH. Understand conjugate acid–base pairs, buffer action, and hydrolysis of salts (which salts give acidic, basic or neutral solutions). Know neutralisation, titration curves and indicators. Recognise amphoteric substances and the role of water autoionisation.
Traps
- Assuming strong concentration means strong acid; strength and concentration differ.
- Forgetting that pH + pOH = 14 only at 25 °C.
- Ignoring hydrolysis: salts of weak acids and strong bases are basic.
- Misreading titration curves for weak acids (buffer region, equivalence pH > 7).
Worked example
Find the pH of 0.01 mol dm⁻³ HCl. HCl is strong, so [H⁺] = 0.01 mol dm⁻³ and pH = −log(0.01) = 2. For a weak acid, use Ka and an ICE table; for a buffer, use the Henderson–Hasselbalch relation pH ≈ pKa + log([A⁻]/[HA]). Rule of thumb: strong acid pH = −log C; weak acid pH > −log C.