Acid strength, concentration and pH scale reasoning
≈ 50 minAcid strength, concentration and pH scale reasoning
Acid strength describes the extent of ionisation in water, while concentration describes amount of solute per volume. A strong acid such as hydrochloric acid is modelled as ionising almost completely in dilute aqueous solution; a weak acid establishes an equilibrium with undissociated molecules. The pH scale compresses very small hydrogen-ion concentrations using a logarithm. For simple strong-acid problems, [H⁺] can be used directly to calculate pH. Tenfold changes in [H⁺] shift pH by one unit. Use indicators as approximate evidence and pH meters for quantitative measurement, while recognising calibration and temperature can affect readings.
Work it through
A solution with [H⁺] = 1.0 × 10⁻² mol dm⁻³ has pH 2. A solution of pH 3 has ten times lower [H⁺] than pH 2, not three times lower. A highly concentrated weak acid and a dilute strong acid cannot be ranked by the words strong and weak alone; use concentration or pH data.
Mastery target
Separate strength from concentration, use the logarithmic pH scale and compare hydrogen-ion concentrations by factors of ten.
What does the term strong acid describe?
Name the key chemistry term from Acid strength, concentration and pH scale reasoning that best fits the explanation and visual model.
What is the pH of a solution with [H⁺] = 1.0 × 10⁻² mol dm⁻³?
Which statement corrects a common misunderstanding in Acid strength, concentration and pH scale reasoning?