Volumetric Analysis: Detailed Notes
Expanded guide with principles, titration types, apparatus, errors, calculations, and practice MCQs
1. Introduction to Volumetric Analysis
Definition: Volumetric analysis (titrimetric analysis) is a branch of quantitative analytical chemistry where a known solution reacts with an unknown to determine its concentration.
2. Titration Basics
- Burette: Contains titrant of known concentration.
- Conical Flask: Contains analyte and indicator.
- Pipette: Delivers a fixed analyte volume.
- Equivalence Point: Stoichiometric completion of reaction.
- End Point: Experimentally observed point (usually via indicator).
At Equivalence Point: moles of titrant = moles of analyte (adjusted by stoichiometry)
n1M1V1 = n2M2V2
3. Standard Solutions
Primary Standards
- High purity, stable, non-hygroscopic, high molar mass.
- Examples: Sodium carbonate (Na₂CO₃), Oxalic acid, K₂Cr₂O₇.
Secondary Standards
Prepared by titrating against a primary standard. Examples: NaOH, HCl, KMnO₄.
4. Types of Titrations
4.1 Acid–Base Titrations
Based on neutralization reaction between an acid and a base.
- Strong acid vs strong base → equivalence at pH 7.
- Weak acid vs strong base → equivalence > 7 (basic).
- Strong acid vs weak base → equivalence < 7 (acidic).
4.2 Redox Titrations
Involves transfer of electrons between species.
- Permanganometry: KMnO₄, self‑indicator (purple → colourless).
- Dichrometry: K₂Cr₂O₇ with diphenylamine as indicator.
- Iodometry/Iodimetry: Uses iodine; starch solution as indicator.
4.3 Precipitation Titrations
Formation of insoluble precipitate.
- Mohr Method → Cl⁻ with AgNO₃ using K₂CrO₄ as indicator.
- Volhard Method → Back titration (Fe³⁺ as indicator with thiocyanate).
- Fajans Method → Adsorption indicators (fluorescein).
4.4 Complexometric Titrations
Based on metal ion–ligand complex formation.
Indicators: Eriochrome Black‑T, Murexide.
Applications: Water hardness determination (Ca²⁺, Mg²⁺).
5. Indicators
Chosen so their colour change coincides with the equivalence point of titration curve.
6. Calculations in Volumetric Analysis
1:1 Reactions: M₁V₁ = M₂V₂
General Case: n₁M₁V₁ = n₂M₂V₂
Normality: N₁V₁ = N₂V₂
Normality = Molarity × Valency Factor
7. Common Apparatus in Volumetric Analysis
- Pipette (fixed, accurate volume transfer).
- Burette (measures variable titrant volume).
- Volumetric Flask (prepares precise solution).
- Conical Flask (reaction vessel).
8. Sources of Error
- Random errors: Reading fluctuations, parallax errors.
- Systematic errors: Glassware calibration, impure reagents.
- Personal errors: Misjudging meniscus/colour change.
Practice MCQs
| Question | Options |
|---|---|
| 1. Primary purpose of volumetric analysis? | a) Mass b) Concentration ✔ c) Boiling point d) Purity |
| 2. The solution of known concentration? | a) Analyte b) Indicator c) Titrant ✔ d) Solute |
| 3. Equivalence point means? | a) End point b) Transition point c) ✔ Stoichiometric equivalence d) Saturation |
| 4. Example of a primary standard? | a) NaOH b) HCl c) KMnO₄ d) ✔ Na₂CO₃ |
| 5. Which indicator for weak acid–strong base titration? | a) Methyl orange b) ✔ Phenolphthalein c) Litmus d) BTB |
Answer Key (Selected)
Q1: (b) Concentration → determines unknown concentration.
Q2: (c) Titrant → standard solution in burette.
Q3: (c) Equivalence point → stoichiometric completion.
Q4: (d) Na₂CO₃ → pure, stable, suitable as primary standard.
Q5: (b) Phenolphthalein → works best as equivalence pH > 7.