Titration
Titration determines unknown concentration by adding a titrant until the equivalence point. Acid-base, redox, and complexometric titrations use indicators or potential to detect the endpoint.
Why This Chemistry Calculation Matters
Why: Titration is the gold standard for determining unknown concentrations. The equivalence point is when stoichiometrically equivalent amounts have reacted.
How: M₁V₁n₁ = M₂V₂n₂. Choose an indicator whose transition pH lies within the steep part of the titration curve. Acid-base, redox, and complexometric use different detection methods.
- ●Equivalence point: moles titrant = moles analyte (× stoichiometry).
- ●Indicator transition pH should fall within ±1 pH of equivalence.
- ●EDTA forms 1:1 complexes; KMnO₄ is self-indicating for redox.
- ●Back titration: add excess titrant, then titrate the excess.
Compact Examples
Inputs
For educational and informational purposes only. Verify with a qualified professional.
🔬 Chemistry Facts
Equivalence point: stoichiometrically equivalent amounts reacted.
— IUPAC
Phenolphthalein: colorless→pink at pH 8.3–10.0.
— Analytical
EDTA 1:1 with Ca²⁺/Mg²⁺ for water hardness.
— Complexometry
KMnO₄ self-indicating: purple→colorless at endpoint.
— Redox
📋 Key Takeaways
- • M₁V₁n₁ = M₂V₂n₂ — Equivalence point calculation with stoichiometry
- • Acid-base | Strong-strong pH=7; weak-strong basic at equivalence
- • Redox | E_eq = (n₁E°₁ + n₂E°₂)/(n₁ + n₂)
- • Indicator | Choose transition pH near equivalence point
Did You Know?
The equivalence point is when moles of titrant = moles of analyte (accounting for stoichiometry).
Source: IUPAC
Phenolphthalein changes from colorless to pink at pH 8.3–10.0, ideal for weak acid–strong base.
Source: Analytical chem
EDTA forms 1:1 complexes with most metal ions; water hardness is often measured by EDTA titration.
Source: Complexometry
KMnO₄ is self-indicating: purple MnO₄⁻ reduces to colorless Mn²⁺ at the endpoint.
Source: Redox
Back titration is used when the analyte reacts slowly or the endpoint is hard to detect directly.
Source: Harris
For polyprotic acids, each equivalence point corresponds to neutralization of one proton.
Source: Acid-base
How Titration Works
Titration adds a titrant of known concentration to an analyte until the equivalence point. Use M₁V₁n₁ = M₂V₂n₂ to find unknown concentration or volume.
Equivalence Volume
V₂ = (M₁V₁n₁)/(M₂n₂)
Unknown Concentration
M₁ = (M₂V₂n₂)/(V₁n₁)
Expert Tips
Indicator Choice
Select indicator whose transition pH lies within the steep part of the titration curve.
Stoichiometry
Always account for n₁ and n₂ (e.g., 5:1 for Fe²⁺ vs MnO₄⁻).
Weak Acids
Equivalence pH > 7 for weak acid + strong base; use phenolphthalein.
Back Titration
Analyte = initial titrant − back titrant (both in moles).
Indicator Comparison
| Indicator | Acid Color | Base Color | pH Range | Transition pH |
|---|---|---|---|---|
| Methyl Orange | Red | Yellow | 3.1-4.4 | 3.7 |
| Bromophenol Blue | Yellow | Blue | 3.0-4.6 | 4 |
| Methyl Red | Red | Yellow | 4.4-6.2 | 5.1 |
| Bromothymol Blue | Yellow | Blue | 6.0-7.6 | 7 |
| Phenolphthalein | Colorless | Pink | 8.3-10.0 | 9.3 |
| Thymol Blue | Yellow | Blue | 8.0-9.6 | 9 |
| Alizarin Yellow | Yellow | Red | 10.1-12.0 | 11 |
Frequently Asked Questions
What is the equivalence point?
The point where stoichiometrically equivalent amounts of analyte and titrant have reacted. M₁V₁n₁ = M₂V₂n₂.
Why does weak acid + strong base give pH > 7 at equivalence?
The conjugate base hydrolyzes: A⁻ + H₂O ⇌ HA + OH⁻, making the solution basic.
How do I choose an indicator?
The indicator transition pH should fall within the steep part of the titration curve (typically ±1 pH of equivalence).
What is back titration?
Excess titrant is added to the analyte, then the excess is titrated with a second reagent. Used when direct titration is difficult.
Why use EDTA for water hardness?
EDTA forms stable 1:1 complexes with Ca²⁺ and Mg²⁺. Eriochrome Black T indicates the endpoint.
What is the Nernst equation used for in redox titration?
To calculate cell potential before, at, and after the equivalence point based on concentration ratios.
How does stoichiometry affect equivalence volume?
For 5Fe²⁺ + MnO₄⁻, 5 moles Fe²⁺ react with 1 mole MnO₄⁻; n₁=5, n₂=1 in the formula.
Key Numbers
Official Data Sources
⚠️ Disclaimer: This calculator uses IUPAC definitions for titration and the CₐVₐ = CbVb equation. For precise work, consult IUPAC Gold Book (titration terminology), Harris (Quantitative Chemical Analysis), and ISO 6353 for reagent and titration standards. Actual results may vary with temperature, indicator selection, and solution purity.
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