Acid-Base Titration Formula and Calculator
Acid-Base Titration Formula and Calculator
Find the unknown concentration or volume at the equivalence point, with indicator choice and NaOH standardisation.
What is an acid-base titration?
A titration finds the concentration of a solution by reacting it with a solution of known concentration (the titrant). The titrant is added from a burette until the equivalence point, where equivalents of acid equal equivalents of base. An indicator colour change marks the end point.
Titration formula
Worked examples
Example 1: HCl with NaOH
25 mL of HCl is titrated with 0.1 M NaOH; the end point is at 20 mL. What is the HCl molarity?
- Ma × 25 × 1 = 0.1 × 20 × 1
- Ma = 2 ÷ 25 = 0.08 M
Answer: 0.08 M.
Example 2: H2SO4 with NaOH
10 mL of H2SO4 is neutralised by 15 mL of 0.2 M NaOH. What is the H2SO4 molarity?
- Ma × 10 × 2 = 0.2 × 15 × 1
- Ma = 3 ÷ 20 = 0.15 M
Answer: 0.15 M (0.30 N).
Example 3: standardising NaOH with KHP
0.4084 g of potassium hydrogen phthalate (KHP, 204.22 g/mol) needs 20.00 mL of NaOH. What is the NaOH molarity?
- n KHP = 0.4084 ÷ 204.22 = 0.002000 mol
- n NaOH = n KHP
- M NaOH = 0.002000 ÷ 0.02000 L = 0.1000 M
Answer: 0.1000 M.
Choosing an indicator
| Indicator | pH range | Colour change | Use for |
|---|---|---|---|
| Phenolphthalein | 8.2 – 10.0 | colourless → pink | strong/weak acid with strong base |
| Methyl red | 4.4 – 6.2 | red → yellow | strong acid with weak base |
| Methyl orange | 3.1 – 4.4 | red → yellow | strong acid with weak base, carbonate |
| Bromothymol blue | 6.0 – 7.6 | yellow → blue | strong acid with strong base |
Choose an indicator whose range includes the pH at the equivalence point. A weak acid titrated with a strong base has its equivalence point above pH 7, so phenolphthalein suits it better than methyl orange.
Good titration practice
- Rinse the burette with titrant, fill it and remove air bubbles from the tip.
- Pipette the sample into an Erlenmeyer flask and add 2–3 drops of indicator.
- Add titrant while swirling; slow down as the colour lingers.
- Stop when the colour persists for 30 seconds and read the meniscus at eye level.
- Repeat at least three times and average results that agree within 0.10 mL.
Frequently asked questions
What is the difference between equivalence point and end point?
The equivalence point is the theoretical point of complete reaction; the end point is when the indicator changes colour. A suitable indicator makes them nearly the same.
What is a primary standard?
A very pure, stable substance that can be weighed directly to make a solution of exact concentration, such as KHP, Na2CO3 or oxalic acid.
Does this formula work for redox titrations?
Yes, replace valence with electrons transferred, or use normality: N1 × V1 = N2 × V2.
How precise is a burette?
A class A 50 mL burette typically has a tolerance of ± 0.05 mL and is read to 0.01 mL.
Prepare solutions with analytical-grade reagents
AMI Scientific is one of the official TCI distributors in Indonesia. Reagents with lot CoA & SDS, formal quotations and tax invoices for universities and laboratories.
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