Acids and bases — Grade 12 Past Paper Questions

Back-titration to determine hydroxide content in an antacid mixture. Excess hydrochloric acid reacts with aluminium and magnesium hydroxides; the remaining acid is neutralised with sodium hydroxide solution. Calculate total moles of hydroxide ions and the mass of aluminium hydroxide present.

Oxalic acid ionisation and acid-base properties. Questions address weak acid definition, conjugate pairs, diprotic nature, ampholytic character, concentration calculations from mass, titration with sodium hydroxide, indicator selection, and pH calculation when excess magnesium hydroxide neutralises nitric acid.

Water ionisation equilibrium and temperature effects on Kw. Calculate hydronium concentration at elevated temperature, determine whether ionisation is exothermic or endothermic, analyse pH changes with temperature, identify water's ampholytic reactions, define electrolytes, and rank acid strength by Ka values.

Multiple-choice page covering Arrhenius acid definition, hydrolysis and pH of sodium nitrate solution, spontaneous redox reaction between iron and chromium III ions, and electrolysis of concentrated sodium chloride with cathode products and pH changes.

Multiple-choice questions on writing the reaction equation from an equilibrium constant expression, and distinguishing the endpoint from the equivalence point in a titration.

Multiple-choice covering energy profile analysis for reversible reactions, identifying activation energy components, effect of catalysts, and acid-base indicator equilibrium shifts using Le Chatelier's principle.