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Buffer Solution pH Calculator

Henderson-Hasselbalch equations, buffer resistance, and step-by-step examination working

Common Presets

Acid Constant (Ka or pKa)

pKa

Ka (mol dm⁻³)

Equilibrium Concentrations

[Weak Acid] HA (mol dm⁻³)

[Conjugate Base] A⁻ (mol dm⁻³)

Calculated pH 4.76 [H⁺] = 1.74 × 10⁻⁵ mol dm⁻³

Step-by-Step Mark Scheme Breakdown

Common Presets

Base Constant (Kb or pKb)

pKb

Kb (mol dm⁻³)

Equilibrium Concentrations

[Weak Base] B (mol dm⁻³)

[Conjugate Acid] BH⁺ (mol dm⁻³)

Calculated pH 9.25 pOH = 4.75 | [OH⁻] = 1.78 × 10⁻⁵ mol dm⁻³

Step-by-Step Mark Scheme Breakdown

Initial Buffer System (Volume: 1.0 dm³)

Acid pKa

Initial [HA] (mol dm⁻³)

Initial [A⁻] (mol dm⁻³)

Reagent Added

Added Reagent Amount

Amount Added (mol)

pH Shift 4.67 Initial: 4.76 → Final: 4.67 (ΔpH = -0.09)

Step-by-Step Mark Scheme Breakdown

Examination Key Point: In both AQA, OxfordAQA (CH03), and IB (Topic R3.1), examiners expect you to write the general equilibrium equation first (Ka = ([H⁺][A⁻]) / [HA]), state that [HA]eq ≈ [HA]initial and [A⁻]eq ≈ [salt]initial, and record pH to 2 decimal places.

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