Redox Titration Calculator
Work through redox titration calculations with the electron moles shown: find an unknown concentration, the volume needed for the reaction, or the result of an indirect iodine titration with thiosulfate. Pick a substance and the electron count is filled in from its half-reaction.
Side with the known electron count (standard solution)
Side to solve
Oxidizer
Reducer
Oxidizer
Sodium thiosulfate Na₂S₂O₃
Electrons accepted by the oxidizer = moles of thiosulfate used (1 e⁻ per S₂O₃²⁻)
The coefficient of e⁻ in the half-reaction is the electron count. Pick a substance to fill in the half-reaction and count.
Try an example
Choose a pattern and enter the values and electron counts.
Done
Redox Titration Calculator
How to use
- 1
Pick a pattern
Choose unknown concentration, required volume, or indirect iodine titration with thiosulfate.
- 2
Choose substances and enter values
Picking an oxidizer or reducer fills in the half-reaction and electron count. Enter concentrations (mol/L) and volumes (mL).
- 3
Check the working
Follow the electron moles, the equality, and the final concentration or volume, with a significant-figure note.
Features
- Three patterns: unknown concentration, required volume, indirect iodine titration
- Pick a substance to fill in its half-reaction and electron count (KMnO₄ = 5, K₂Cr₂O₇ = 6 and so on)
- Shows the working: electron moles, the equality, then the answer
- Makes clear that the electron count is the e⁻ coefficient of the half-reaction
- Runs entirely in your browser; no sign-up and nothing uploaded
Use cases
Check homework
Verify redox titration problems with the electron working shown.
Review half-reactions
See each substance’s electron count and half-reaction on the spot, so there is less to memorise.
Plan iodometry
Work out the thiosulfate volume needed, or back-calculate the oxidizer concentration.
Details
A redox titration drips a solution of known concentration (the standard solution) into a solution of unknown concentration until they exactly react. In an acid-base titration the amounts of H⁺ and OH⁻ balance; in a redox titration it is the amount of electrons (e⁻) transferred that balances.
The calculation uses "electrons × moles". If one mole of the oxidizer accepts n electrons and one mole of the reducer releases m, then n × (moles of oxidizer) = m × (moles of reducer). The electron count is the coefficient of e⁻ in the half-reaction: 5 for acidic permanganate, 6 for dichromate, 2 for oxalic acid or hydrogen peroxide as a reducer, and 1 for iron(II) ions or thiosulfate.
In an indirect iodine titration, excess potassium iodide is added to the oxidizer and the liberated iodine is titrated with sodium thiosulfate. Electrons simply pass along the chain oxidizer → I₂ → thiosulfate, so the electrons accepted by the oxidizer equal the moles of thiosulfate used (1 e⁻ per S₂O₃²⁻). This lets you determine oxidizers that are difficult to titrate directly.
FAQ
How is this different from an acid-base titration?
In an acid-base titration the amounts of H⁺ and OH⁻ (valence × concentration × volume) balance. In a redox titration the amount of electrons (electrons × moles) balances. The meaning of the "valence" changes from the number of H⁺ to the number of e⁻.
How do I decide the electron count?
It is the coefficient of e⁻ in the half-reaction: 5 for acidic permanganate, 6 for dichromate, 2 for oxalic acid or hydrogen peroxide as a reducer, and 1 for iron(II) ions, iodide ions or thiosulfate. This tool fills in the count and the half-reaction when you pick a substance.
Should I enter volumes in mL or L?
Use mL. The tool converts to litres internally. In the equality the units cancel as long as both sides match, so mL works for the ratio too.
In indirect iodometry, why do the electrons equal the moles of thiosulfate?
The electrons accepted by the oxidizer pass to iodine and then to thiosulfate. Because electrons are conserved, electrons accepted by the oxidizer equal the moles of sodium thiosulfate used (1 e⁻ per S₂O₃²⁻).
How should I handle significant figures?
The display uses three significant digits as a guide. Round once at the end to match the digits given in your problem (often three).
Related Tools
Acid-Base Titration Calculator
Work through acid-base titration calculations with the mole working shown: find an unknown concentration, the volume needed for neutralization, or the original concentration after dilution. Enter the acid and base valences directly.
Moles & Molarity
Calculate molarity from moles and solution volume, or convert mass to moles with a supplied molar mass. View results in mol/L and mmol/L.
Significant Figures Calculator
Count significant figures, round to a chosen precision, and apply the multiplication/division or addition/subtraction rules. Switch between half-up and JIS Z 8401 half-even rounding; scientific notation is shown alongside.
Dilution Calculator
Find the required stock volume from stock concentration, target concentration and final solution volume using C₁V₁ = C₂V₂.
All processing happens in your browser. Your files are never uploaded.
Verified: Textbook cases (standardising KMnO₄ giving 0.0250 mol/L, Fe²⁺ giving 0.50 mol/L, the KMnO₄ volume for H₂O₂ giving 20.0 mL, and indirect iodometry giving 12.0 mL of thiosulfate and 0.0200 mol/L K₂Cr₂O₇) plus error handling are covered by browser tests
Did you know?
In a redox titration it is the amount of electrons (e⁻), not H⁺ and OH⁻, that balances. The electron count is the coefficient of e⁻ in the half-reaction: 5 for acidic permanganate and 6 for dichromate. Permanganate also acts as a self-indicator, since its colour marks the end point.