Acid-base titrations
Chemistry· Reactivity 3.1· 12 min read
1. Titration Concentration Calculations★★★☆☆⏱ 10 min
✓ Calculator OK
All titration calculations follow a 4-step stoichiometric workflow, using the average of your concordant titre volumes to reduce random error. You must use the mole ratio from the balanced reaction equation to relate moles of acid and base.
Titration calculation formula
Where and are the stoichiometric coefficients of the acid and base in the balanced reaction equation.
Example:
For the 1:1 reaction HCl + NaOH → NaCl + H₂O, so .
A 25.0 cm³ sample of 0.120 mol dm⁻³ H₂SO₄ is titrated against unknown KOH solution. The average concordant titre is 24.6 cm³. Find the concentration of KOH.
- 1
Write the balanced reaction equation to get the mole ratio:
- 2
Calculate moles of H₂SO₄, converting volume to dm³:
- 3
Use 1:2 mole ratio to find moles of KOH:
- 4
Calculate concentration of KOH using titre volume:
2. Common Pitfalls
Wrong move:
Forgetting to convert cm³ to dm³ before calculating moles
Why:
Standard concentration units are mol dm⁻³, so volume must be divided by 1000 to match units
Correct move:
Always convert all volume values to dm³ before performing any titration calculation
Wrong move:
Rinsing the conical flask with the analyte solution
Why:
Residual analyte adds unmeasured extra moles, leading to artificially high titre volumes
Correct move:
Rinse the conical flask only with distilled water; residual water does not change total moles of analyte
Wrong move:
Assuming all equivalence points have a pH of 7
Why:
Only strong acid-strong base titrations produce a neutral salt at equivalence; other combinations make acidic or alkaline salts
Correct move:
Use the identity of the salt formed at the equivalence point to determine if pH is below, equal to, or above 7
Wrong move:
Using phenolphthalein for a strong acid-weak base titration
Why:
Phenolphthalein changes colour above pH 8, outside the steep vertical jump of this titration curve
Correct move:
Use methyl orange, whose 3.1-4.4 pH range falls fully within the strong acid-weak base titration jump
Wrong move:
Stopping the titration at the first faint colour change and not repeating
Why:
Single titre values often have large random error, leading to incorrect final concentration values
Correct move:
Repeat titrations until you get two concordant titres within 0.1 cm³, then use the average of these two values
3. Quick Reference Cheatsheet
Titration Type | Equivalence pH | Suitable Indicator | Indicator pKa |
|---|---|---|---|
Strong acid + Strong base | 7 | Methyl orange / Phenolphthalein | 3.7 / 9.3 |
Strong acid + Weak base | <7 | Methyl orange | 3.7 |
Weak acid + Strong base |
| Phenolphthalein | 9.3 |
Weak acid + Weak base | ~7 | No suitable indicator | N/A |
4. Frequently Asked
Can I use phenolphthalein for a strong acid-strong base titration?
Yes, phenolphthalein is fully suitable as its pH range of 8.2-10.0 falls entirely within the steep vertical region of the strong-strong titration curve.
When this came up on past exams
AI-estimated based on syllabus patterns — cross-check with official past papers for accuracy. Use only as revision-focus signals.
- 2025 · 2
Strong acid-weak base titration calculation
- 2023 · 3
Volumetric glassware error analysis
What's Next
Mastering acid-base titrations gives you a foundational quantitative skill that is tested across 3 separate IB Chemistry SL assessment objectives, from practical Paper 2 skills to Paper 2 extended response calculations. This knowledge directly transfers to related acid-base equilibrium topics, including buffer solution behaviour and pH calculation for salt solutions. You will also use the same volumetric analysis workflow later in the course for redox titrations, which are a common 6+ mark extended question on past papers. Solidify this knowledge by working through 2-3 past paper titration calculation questions to lock in your workflow before moving on to more advanced equilibrium content.