Acids & bases (every paper)

Strength ≠ concentration. pH with correct sig figs. Spot conjugate pairs.

Strong (HCl)	Weak (CH₃COOH)
Ionisation	Complete	Partial — equilibrium lies left
0.10 mol L⁻¹ pH ≈	1.0	~2.9 (fewer H₃O⁺ than molecules)
Conductivity	High	Low — few ions

"Same pH, different concentrations" comparisons are the Excellence move.

Exam-style pH of 0.025 mol L⁻¹ HCl Strong acid → full ionisation. [H₃O⁺] = 0.025 mol L⁻¹ (2 s.f.) pH = −log(0.025) = 1.60 ✓ pH 1.60 — two decimal places to match two significant figures.

Amphiprotic species

A species that can act as EITHER an acid or a base depending on the reaction partner — water and HCO₃⁻ are the standard examples.

Practice for this standard covers the whole topic — flashcards and quiz.