Volumetric Analysis: Detailed Notes
A complete guide with definitions, principles, titrations, calculations, apparatus, errors, and MCQs
1. Introduction to Volumetric Analysis
Definition: A quantitative chemical analysis method that determines the concentration of an analyte by measuring the volume of titrant required to react completely with it.
Principle: Based on a complete and stoichiometric reaction between analyte and titrant.
Advantages: Fast, inexpensive, precise, and accurate for many applications.
2. Titration
- Titration: Process of adding a titrant from a burette to an analyte solution until reaction is complete.
- Titrant: Solution of known concentration.
- Analyte: Substance whose concentration is determined.
- Equivalence Point: Theoretical point where moles of titrant = moles of analyte.
- End Point: Experimental detection point via visible change (often color).
- Titration Curve: Plot of property (pH, potential) vs titrant volume.
3. Standard Solutions
A standard solution is one whose concentration is accurately known.
Primary Standards
- High purity, stability, high molar mass, non-hygroscopic
- Examples: Na₂CO₃, K₂Cr₂O₇, Oxalic acid dihydrate
Secondary Standards
Standardized against primary standards. Examples: NaOH, HCl, KMnO₄.
4. Types of Titrations
4.1 Acid-Base Titrations
Based on neutralization reaction between acids and bases.
- Indicators: Phenolphthalein, Methyl orange, etc.
- Strong Acid vs Strong Base → pH 7 at equivalence.
- Strong Acid vs Weak Base → pH < 7.
- Weak Acid vs Strong Base → pH > 7.
4.2 Redox Titrations
Based on electron transfer between analyte and titrant.
- Examples: Permanganometry, Dichrometry, Iodometry/Iodimetry
4.3 Precipitation Titrations
Reaction involves insoluble precipitate formation.
- Mohr Method, Volhard Method, Fajans Method.
4.4 Complexometric Titrations
Based on stable complex formation (e.g., EDTA titrations).
5. Indicators
Indicators are chosen such that their pH (or potential) transition fits the sharp change in titration curve at equivalence.
6. Calculations
M1V1 = M2V2 (1:1 reactions)
In general: n1M1V1 = n2M2V2
Normality: N1V1 = N2V2
7. Common Apparatus
- Burette: Measures precise volumes of titrant.
- Pipette: Transfers fixed volume of analyte.
- Volumetric Flask: Used for preparing standard solutions.
- Conical Flask: Holds analyte and indicator.
8. Sources of Error
- Random: reading errors, temperature fluctuations.
- Systematic: wrong calibration, impure solutions.
- Personal: parallax errors, inconsistent colour judgment.
Multiple Choice Questions (MCQs)
Choose the correct answer:
| Question | Options |
|---|---|
| Volumetric analysis is primarily used to determine: | a) Mass b) Concentration ✔ c) Boiling Point d) Purity |
| The solution of known concentration is: | a) Analyte b) Titrand c) Titrant ✔ d) Indicator |
| Equivalence Point is: | a) End point b) Transition point c) Equivalence ✔ d) Saturation |
Answer Key (with short explanations)
Q1: Concentration of unknown substance → Volumetric analysis is a quantitative technique.
Q2: Titrant → Solution of known concentration.
Q3: Equivalence point → Theoretical completion of reaction.