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Free back titration questions and generator
Generate unlimited A-level back titration questions, choose the difficulty and scenario, reveal progressive clues, or print a mixed practice set with worked answers.
Several generators, rebuilt as one practice studio
This page provides various back titration question generators. Some allow you to set the difficulty, give you clues and step-by-step worked solutions. They are suitable for all A-level Chemistry students. Traditionally AQA test back titrations a lot, but recently OCR have started to as well.
The old page had several separate generators. They are now combined into one maintained practice studio: use guided mode while learning the method, then switch to mixed or harder exam practice. Every numerical question is generated from a chemically consistent hidden answer, so the titre and percentage purity agree rather than being decorative random numbers.
Give your answer to three significant figures unless the question suggests otherwise.
How to solve a back titration
- Find the amount initially added. Convert the reagent volume from cm³ to dm³ and use n = cV.
- Use the titration to find the excess. The titre tells you how much reagent remained after the original reaction.
- Scale an aliquot back to the full solution. Apply the volumetric-flask dilution factor before subtracting.
- Subtract the excess from the initial amount. This gives the amount that reacted with the sample.
- Use the chemical equation. Convert the reacted acid into moles and mass of the pure component.
- Calculate percentage purity. Divide the pure-component mass by the original sample mass and multiply by 100.
The titre measures what was left over, not what reacted with the sample. Subtraction is the defining step.
A purity above 100% usually means a missing dilution factor, an inverted subtraction or the wrong reaction ratio.
The harder mode keeps the spirit of the old generator inspired by a particularly demanding AQA Year 13 question: fewer prompts, less friendly ratios and no convenient invitation to skip the equation.
Why back titration is used
Direct titration may be unsuitable when a solid reacts slowly, is insoluble, or does not give a sharp endpoint. A measured excess of reagent is allowed to react completely, then the unused excess is determined by a second titration.