3.1.6—Strong vs. weak acids/bases
- Syllabus
- First assessment 2025
- Objective
- 3.1.6
- Level
- HL
Strong and Weak Acids and Bases
A strong acid or base ionizes completely in aqueous solution; a weak acid or base ionizes only partially. The equilibrium favours the weaker conjugate species.
Strength is the extent of ionization, whereas concentration is the amount of solute per volume. A concentrated weak acid can be more acidic than a dilute strong acid.
Represent a strong acid with essentially complete ionization and a weak acid with an equilibrium containing substantial undissociated acid. Strength is an equilibrium property, while concentration is an initial amount per volume; pH depends on both, so strength alone cannot rank arbitrary solutions.
Distinguishing Strength from Concentration
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Explain the difference in pH .
nitrous acid/ HNO2 is not fully dissociated/is a weak acid.
OR
HCI is fully dissociated/is a strong acid.
«HNOX2» lower concentration of H+ions
OR
«HCl» higher concentration of H+ions.
Proton Transfer Reactions Summary
Retrieve the route: track proton transfer and conjugates, calculate pH and Kw, distinguish strength, balance neutralization, read titration curves, use Ka/Kb and hydrolysis, select indicators, and explain and calculate buffer behaviour.
Check donor versus acceptor, one-proton differences, logarithm direction, ion comparison, strength versus concentration, equivalence versus endpoint, pKa landmarks, conjugate equations and dilution ratios.