Iodometric Titration Calculator

Plan and analyze redox titrations using iodine/thiosulfate chemistry. Compute analyte concentration, titrant volume, or reaction stoichiometry. Supports units M, mM, µM, g/L, %, and mL, L. Fully offline—your data never leaves your browser.

Educational only. Follow your lab SOPs and SDS. Handle iodine and strong oxidizers/reducers with proper PPE and ventilation.

Results

Primary Result

0.0507 M

Analyte concentration

Intermediate Values

Moles S₂O₃²⁻ used: 1.52e-3 mol
Moles I₂ produced: 7.60e-4 mol
Moles of analyte: 1.267e-4 mol
Effective n-factor: 6.00

Unit Consistency: All volumes converted to L, concentrations to M before calculation.

Understanding Iodometric Titrations

Iodometric titration is an indirect redox method where an oxidizing analyte liberates iodine from iodide, and the iodine is titrated with standardized sodium thiosulfate. This tool helps you plan experiments, check calculations, and understand stoichiometry.

Step‑by‑Step Usage

Select your calculation goal (analyte concentration, titrant volume, or verify n‑factor).
Enter the known values with correct units. Use the unit selectors to match your lab data.
The n‑factor is crucial: moles of thiosulfate consumed per mole of analyte. For KIO₃, it’s 6; for H₂O₂, it’s 2.
Press Calculate. Review intermediate values to verify the redox conversion.
Use Copy Result or manually note the result for your lab notebook.

Realistic Examples

Analyte	Given Values	Result	Notes
Potassium iodate (KIO₃)	C_thio = 0.100 M, V_thio = 15.20 mL, V_analyte = 25.00 mL, n = 6	0.01013 M KIO₃	Classic standardization.
Hydrogen peroxide (H₂O₂)	C_analyte ≈ 3% w/v (≈0.88 M), V_analyte = 10.0 mL, C_thio = 0.05 M, n = 2	V_thio ≈ 35.2 mL	Convert % w/v using molar mass (34.01 g/mol).
Copper(II) ions	C_thio = 0.102 M, V_thio = 24.75 mL, V_analyte = 50.0 mL, n = 2	0.0252 M Cu²⁺	After reduction of Cu²⁺ to CuI, iodine is released.

Common Mistakes Checklist

Using the wrong n‑factor for the analyte redox half‑reaction.
Forgetting that starch indicator should be added near the endpoint (pale yellow), not at the start.
Not accounting for iodine volatility – titrate quickly, avoid excessive stirring in open air.
Using old thiosulfate solution (microbial degradation, oxidation) without re‑standardization.
Ignoring pH effects: the thiosulfate‑iodine reaction requires near‑neutral pH.

Quick Concentration Converter

Convert between molarity, g/L, and % w/v for your analyte. Enter any value and see equivalents.

Molarity (M)

g/L

% w/v

Molar Mass (g/mol)

0.1 M = 21.4001 g/L = 2.140 % w/v

Frequently Asked Questions

What is the n‑factor and how do I determine it?

The n‑factor is the number of moles of thiosulfate ions (S₂O₃²⁻) consumed per mole of analyte. It comes from the redox stoichiometry. For example, KIO₃ releases 3 I₂, each I₂ consumes 2 S₂O₃²⁻, so n = 6. Check balanced equations for your system.

When does the iodometric method fail or become inaccurate?

In strongly acidic (pH < 2) or alkaline (pH > 9) conditions, side reactions occur. Volatile iodine can be lost if titration is too slow or in open vessels. Strong oxidizing agents that oxidize iodide beyond I₂ (e.g., permanganate) need special procedures.

What are common unit pitfalls?

Mixing mL and L is the most frequent error. Always double‑check volume units. For % w/v, you must provide molar mass to convert to molarity. The calculator warns if volumes differ by 1000‑fold.

Any tips for precise measurement?

Use a burette with ±0.05 mL readability. Standardize thiosulfate weekly with KIO₃. Add starch only when the solution is pale yellow to avoid complexation issues. Control temperature – thiosulfate titer changes over time.

Safety notes for iodometric titrations?

Iodine is a skin irritant and vapor can irritate eyes/respiratory tract. Work in a fume hood or well‑ventilated area. Wear gloves and safety glasses. Neutralize waste solutions (thiosulfate reduces residual iodine) before disposal per local regulations.

Formulas & Assumptions

Core equation: n_analyte = (C_thio × V_thio) ÷ n‑factor

Concentration: C_analyte = n_analyte ÷ V_analyte

Unit conversions: 1 M = 1000 mM = 10⁶ µM; g/L → M = (g/L) ÷ molar mass; % w/v → g/L = (% w/v) × 10.

Assumptions: Complete liberation of I₂, quantitative reaction with thiosulfate, no side reactions, neutral pH, fresh starch endpoint.

Rounding: Results rounded to selected decimal places or to 4 significant figures if “Significant figures” is chosen. Intermediate values keep higher precision.

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Iodometric Titration Calculator

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