Follow the proton.
A Brønsted–Lowry acid donates a proton; a base accepts one. A conjugate pair differs by exactly one , so both the hydrogen count and charge change. HCO₃⁻ can accept or donate a proton and is amphiprotic.
Strong and weak describe the extent of ionisation. Concentrated and dilute describe the amount dissolved per volume. Diluting a strong acid does not make it a weak acid. Monoprotic, diprotic and polyprotic refer to the number of protons an acid can donate in stages.
HCl and HNO₃ are strong acids; ethanoic and carbonic acids are weak. Group 1 hydroxides and Ba(OH)₂ are strong bases; ammonia and amines are weak bases. Sulfuric acid is classified as strong, but its second ionisation is not generally complete at all concentrations.
Strong is not concentrated
At 25 °C. Compare HCl with a model weak acid (Ka = 1.8 × 10⁻⁵). The pH calculation includes water; particle counts are schematic.
Assumed knowledge
Charges must balance; removing H⁺ makes a species one charge more negative.
Learning checkpoints & source
YOUR SYLLABUS CHECKPOINT- Identify proton donors, acceptors and conjugate pairs.
- Distinguish strength from concentration.
- Identify amphiprotic species.