What is Titration?
Titration is an analytical technique in which a known solution (titrant) is gradually added to an unknown sample until the reaction reaches the equivalence point. The volume of titrant used determines the sample's concentration. It is precise, widely used, and based on stoichiometry.
In acid-base titration, a standardized acid or base is added to an unknown solution until the equivalence point (equal moles of acid and base). An indicator detects this point by colour change, and concentration is calculated from the volume used.
- 1↓1. PrepareFill burette with standardized titrant
- 2↓2. Add samplePlace known volume of analyte in flask
- 3↓3. TitrateGradually add titrant while swirling
- 4↓4. Detect endpointIndicator colour change signals equivalence point
- 5↓5. Record volumeNote volume of titrant used
- 66. CalculateUse M₁V₁ = M₂V₂ to find analyte concentration
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Step-by-step worked examples
20 mL of 0.1 M NaOH was required to titrate 25 mL of HCl. Calculate the molarity of HCl.
For HCl + NaOH → NaCl + H₂O, mole ratio is 1:1 M₁V₁ = M₂V₂ 0.1 M × 20 mL = M₂ × 25 mL M₂ = (0.1 × 20) / 25 = 2 / 25 = 0.08 M
A 30 mL sample of H₂SO₄ requires 45 mL of 0.2 M NaOH. Find [H₂SO₄].
For H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O, mole ratio is 1:2 Moles of NaOH used = 0.2 M × 0.045 L = 0.009 mol Moles of H₂SO₄ = 0.009 / 2 = 0.0045 mol [H₂SO₄] = 0.0045 mol / 0.030 L = 0.15 M
Phenolphthalein is the indicator used. At what pH does its colour change occur?
Phenolphthalein is colourless below pH 8.2 At pH 8.2–10.0, it turns pink For strong acid–strong base titrations (endpoint ~pH 7), a different indicator (e.g., methyl orange, pH 3–4) might be better
Flashcards
Quick quiz
Q1.In a titration, 30 mL of 0.5 M HCl required 25 mL of NaOH. [NaOH] = ?
Q2.What is the equivalence point?
Q3.Which indicator is best for a strong acid–strong base titration?
Q4.If 15 mL of 0.2 M H₂SO₄ is titrated with 0.1 M NaOH, volume of NaOH needed is:
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Common mistakes
Titration measures volume only. — Correct: Titration uses volume to determine concentration via stoichiometry and the known concentration of the titrant.
The endpoint and equivalence point are always the same. — Correct: The endpoint is where the indicator signals; the equivalence point is stoichiometric. A good indicator makes them nearly coincide.
All indicators work for all titrations. — Correct: Indicator choice depends on the expected pH at equivalence: choose one whose colour range brackets that pH.
More concentrated titrant means faster completion. — Correct: Concentration of titrant does not affect the volume needed to reach equivalence (only the molarity).
FAQ
What is the titration formula?
M₁V₁ = M₂V₂ for 1:1 mole ratio. Adjust the equation for other stoichiometries (e.g., M₁V₁ = 2M₂V₂ for 1:2).
How do you calculate concentration from titration?
Rearrange M₁V₁ = M₂V₂ to find the unknown: M₂ = (M₁ × V₁) / V₂.
Why is a burette used instead of a graduated cylinder?
A burette has fine graduations (0.1 mL) and a stopcock for precise, controlled delivery of small volumes.
Can titration be used for non-acid–base reactions?
Yes, redox titrations, precipitation titrations and complexometric titrations all use the same stoichiometric principle.