‹ Chemistry simulationsChemistry · A Level 9701 · 25 Equilibria (A Level)Six simulations covering Topic 25: the ionic product of water and the pH of strong acids and bases; weak acids, Ka and pKa with the pH worked out from the approximation and the quadratic; buffer solutions with the Henderson-Hasselbalch equation and the effect of adding acid or base; titration curves for the four acid-base combinations with methyl orange and phenolphthalein; the solubility product and the common ion effect in 3D; and partition coefficients between two solvents.
Water ionises very slightly, and the product of the two ion concentrations is a constant. That one fact links [H⁺], [OH⁻] and pH for every aqueous solution. Pick an acid or a base, change its concentration, and watch the two ions trade places on a logarithmic scale.
A weak acid is only partly dissociated, so its pH cannot be read straight from its concentration. The equilibrium constant Ka does the job. Choose an acid, change the concentration, and see how many molecules actually give up a proton.
A buffer is a weak acid with its conjugate base, both present in quantity. Whatever acid or base you add finds something to react with, so the pH barely moves. Add the same dose to a buffer and to plain water and compare, then change the ratio to set the pH yourself.
Add 0.100 mol dm−3 base to 25.0 cm³ of 0.100 mol dm−3 acid and plot the pH. The shape of the curve depends on whether each partner is strong or weak, and that decides which indicator can mark the equivalence point.
A sparingly soluble salt sets up an equilibrium between the solid and its ions, and Ksp is its equilibrium constant. Dissolve the salt in a solution that already contains one of its ions and the solubility drops. Or mix two solutions and compare the ionic product with Ksp to see whether a precipitate forms.
Shake a solute with two liquids that do not mix and it divides itself between them in a fixed ratio. Choose Kpc and the volume of solvent, see how much X is pulled out of the water, and then compare one large extraction with two smaller ones.
Six interactive simulations for Cambridge A Level Chemistry 9701 topic 25 Equilibria: the ionic product of water Kw and the pH of strong acids and bases, weak acids with Ka, pKa and the pH of 0.100 mol dm-3 ethanoic acid, buffers shown as the same dose of acid or base added to a buffer and to water, titration curves with methyl orange and phenolphthalein for strong and weak acids and bases, the solubility product Ksp with the common ion effect and precipitation shown with 3D ions, and the partition coefficient Kpc with one large extraction compared with two small ones.
Six simulations covering Topic 25: the ionic product of water and the pH of strong acids and bases; weak acids, Ka and pKa with the pH worked out from the approximation and the quadratic; buffer solutions with the Henderson-Hasselbalch equation and the effect of adding acid or base; titration curves for the four acid-base combinations with methyl orange and phenolphthalein; the solubility product and the common ion effect in 3D; and partition coefficients between two solvents.
Acid-base equilibria is a free, browser-based simulation for Cambridge International AS & A Level Chemistry 9701 (topic 25 Equilibria). The course is assessed in Paper 1 (Multiple Choice (AS)), Paper 2 (AS Structured), Paper 3 (Advanced Practical), Paper 4 (A Level Structured), Paper 5 (Planning, Analysis, Evaluation). Syllabus for examination in 2025-2027. There are 6 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.
Full syllabus map: A Level Chemistry 9701 topic 25.
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