Titration Calculator
Calculate an unknown concentration from titration results, account for the stoichiometric ratio, estimate the equivalence pH and choose an indicator that changes at the right point.
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The stoichiometric ratio is the step most often skipped
The relationship is not simply concentration times volume on each side. Sulfuric acid supplies two protons per molecule, so neutralising it takes twice as much monoprotic base as the volumes alone suggest. Forgetting the ratio produces an answer wrong by exactly a factor of two, which is large enough to be obviously wrong and small enough that it can pass unnoticed if nobody checks the magnitude.
The equivalence point is rarely at pH 7
Neutralising a weak acid with a strong base leaves the conjugate base in solution, which is itself basic, so the equivalence point sits above 7, typically between 8 and 9. The reverse case sits below 7. Only a strong acid with a strong base gives 7. This matters because the indicator has to change colour where the pH actually is: phenolphthalein for a weak acid with a strong base, methyl orange for the reverse, and either for strong with strong.
The end point is not the equivalence point
The equivalence point is where the reaction is stoichiometrically complete; the end point is where the indicator changes. They are close when the indicator is chosen correctly and never identical, which is one of the systematic errors in the technique. Titrating to the first permanent faint colour rather than a definite one keeps the difference small, and the difference is why a blank titration is run for precise work.
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Frequently Asked Questions
What is the stoichiometric ratio?
The number of moles of one reactant that react with one mole of the other, taken from the balanced equation. Sulfuric acid supplies two protons per molecule, so the ratio with a monoprotic base is one to two, and ignoring it gives an answer wrong by a factor of two.
Why is the equivalence point not at pH 7?
Because neutralising a weak acid leaves its conjugate base in solution, which is basic, putting the equivalence point above 7. The reverse case sits below 7, and only strong with strong gives exactly 7.
How do I choose an indicator?
It must change colour across the pH where the equivalence point actually is. Phenolphthalein changes around 8.3 to 10 and suits a weak acid with a strong base; methyl orange changes around 3.1 to 4.4 and suits the reverse.
What is the difference between the end point and the equivalence point?
Equivalence is where the reaction is stoichiometrically complete; the end point is where the indicator changes. They are close with a well-chosen indicator and never identical, which is a systematic error in the method.
Why titrate more than once?
Because a single titre carries the reading error of one measurement with no way to detect a mistake. Concordant titres within about 0.1 mL show the technique is consistent, and the first rough titre is normally discarded.
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How to Use
Enter your titre volume and known concentration to find the unknown one.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.