IB Chemistry Redox Titrations: FAQs, Calculations & Exam Tips

A redox titration measures the volume of one solution needed to react completely with a known volume of another, tracked by electron transfer rather than proton transfer. In the current IB Chemistry guide it sits under Reactivity 3.2, Electron transfer reactions, and is examined through calculation questions on Paper 1 and Paper 2, plus practical work in the IA.

An acid-base titration tracks proton transfer to a stoichiometric endpoint, usually flagged by a pH indicator like phenolphthalein. A redox titration tracks electron transfer, and it's often self-indicating — potassium manganate(VII) is famously its own indicator, turning the solution permanent pale pink once all the reducing agent has been used up.

Many redox titrations don't need an added indicator because the reagent itself changes colour sharply at the endpoint — potassium manganate(VII) is deep purple until it's fully reduced, then the solution turns pale pink. Iodine-thiosulfate titrations do need starch, added near the endpoint so the blue-black colour disappears crisply rather than fading gradually.

Redox titration calculations are core content for both SL and HL — every IB Chemistry student meets manganate(VII) and iodine-thiosulfate titrations. HL students go further, using standard electrode potentials from the data booklet to predict feasibility and covering additional redox applications like the Winkler method for dissolved oxygen, which isn't required at SL.

Convert your titre volumes to dm3, use the balanced overall equation's mole ratio to link the two reactants, then apply concentration = moles ÷ volume. The tricky part is always the ratio — manganate(VII) titrations with iron(II) run 1:5, not 1:1, and that's the single most common error I see in mock papers.

Write separate half-equations for oxidation and reduction, balance atoms other than oxygen and hydrogen first, then balance oxygen with H2O and hydrogen with H+, and finally balance charge with electrons. Multiply each half-equation so electron numbers match, then add them together and cancel anything appearing on both sides.

Moles equal concentration (mol dm-3) multiplied by volume in dm3, so always convert cm3 readings by dividing by 1000 first. In redox titrations you then scale by the mole ratio from the balanced equation before finding the unknown concentration — skip that scaling step and every answer comes out five or six times too small or too large.

The single biggest one is ignoring the mole ratio and treating every titration as 1:1 — manganate(VII)/iron(II) is 1:5, dichromate/iron(II) is 1:6. After that, students lose marks for wrong significant figures (match your least precise measurement) and for forgetting units on the final concentration answer.

A full redox titration calculation on Paper 2 typically carries four to six marks, awarded stepwise — moles of the known reagent, the mole ratio, moles of the unknown, then the final concentration — so partial credit is available even if your final number is wrong. Command terms like "calculate" and "determine" expect working shown.

Redox titrations make a solid Internal Assessment because they generate quantitative, repeatable data — think investigating vitamin C content by iodine titration, or determining iron content in a supplement. Examiners assess these against the IA criteria for methodology, data processing with proper uncertainties, and evaluation of sources of error like endpoint overshoot.

Redox titrations aren't conceptually harder, but they demand an extra step: balancing half-equations before you can even start the mole-ratio arithmetic that acid-base titrations skip straight to. Students who are shaky on oxidation states from Reactivity 3.2 tend to find redox titrations tougher purely because that foundation's missing, not because the maths itself is harder.

Yes — HL adds standard electrode potentials, cell potential calculations, and feasibility predictions using the data booklet's electrochemical series, none of which SL students are assessed on. Both levels, though, are expected to handle the same core titration calculations involving manganate(VII), dichromate and iodine-thiosulfate reactions.

The fastest gains come from repeating the calculation steps, not re-reading notes — get your child working through past paper questions with a data booklet in hand, checking the mole ratio every single time. According to the IB, first exams for the current Chemistry guide were held in 2025, so make sure any past papers used match that syllabus.

On RevisionPrep, students working through Reactivity 3.2 can use topic-specific Revision Notes that break down half-equation balancing, a Topical Worksheet of graded titration calculations, and full Mock Papers timed to match real IB conditions — all mapped to the current syllabus rather than outdated topic names.