Unit 1
General and Physical Chemistry
Class 12 Chemistry
Volumetric AnalysisClass 12 Chemistry – Volumetric Analysis Notes PDF
On mobile, swipe inside the PDF to read all pages and pinch to zoom.
Introduction
Unit 1 develops the quantitative foundations required for titration: gravimetric and volumetric analysis, equivalent weight, concentration units, standard solutions, law of equivalence, normality calculations, acid–base titration, redox titration and related numerical problems.
1. Quantitative Chemical Analysis
Gravimetric Analysis
A quantitative method in which the amount of an analyte is determined from a carefully measured mass, usually after converting the analyte into a suitable solid form.
Volumetric Analysis
A quantitative method in which the amount of an analyte is calculated from the measured volume of a solution of known concentration that reacts completely with it.
| Feature | Gravimetric Analysis | Volumetric Analysis |
|---|---|---|
| Main measurement | Mass | Volume |
| Common operation | Precipitation, filtration, drying and weighing | Titration with a standard solution |
| Result based on | Mass relationship | Stoichiometric volume/concentration relationship |
| Typical apparatus | Balance, crucible, filter apparatus | Burette, pipette, volumetric flask, conical flask |
Fig. 1 – Gravimetric vs Volumetric Analysis
2. Equivalent Weight
2.1 Element
Equivalent weight = 40 ÷ 2 = 20 g eq⁻¹
2.2 Acid
Basicity is the number of replaceable H+ ions furnished per molecule in the reaction considered.
Equivalent weight = 98 ÷ 2 = 49 g eq⁻¹
2.3 Base
For this purpose, acidity of a base represents the number of replaceable OH− groups taking part in neutralization.
Equivalent weight = 74 ÷ 2 = 37 g eq⁻¹
2.4 Salt
2.5 Oxidizing and Reducing Agents
For redox substances, the n-factor is the number of electrons accepted or donated per formula unit in the specified reaction. It can depend on reaction conditions and medium.
Fig. 2 – Equivalent Weight Decision Chart
3. Concentration of Solutions
Concentration expresses how much solute is present in a specified amount of solution or solvent.
| Unit | Definition / Formula | Typical Unit |
|---|---|---|
| Mass percentage (w/w) | (Mass of solute ÷ Mass of solution) × 100 | % |
| Mass/volume percentage (w/v) | (Mass of solute in g ÷ Volume of solution in mL) × 100 | % |
| Volume percentage (v/v) | (Volume of solute ÷ Volume of solution) × 100 | % |
| Strength | Mass of solute per litre of solution | g L⁻¹ |
| Molarity (M) | Moles of solute ÷ Volume of solution in litres | mol L⁻¹ |
| Molality (m) | Moles of solute ÷ Mass of solvent in kilograms | mol kg⁻¹ |
| Normality (N) | Gram-equivalents of solute ÷ Volume of solution in litres | eq L⁻¹ |
| Formality (F) | Formula-weight units of solute ÷ Volume of solution in litres | F |
| ppm | Parts of solute per 10⁶ parts of solution | ppm |
| ppb | Parts of solute per 10⁹ parts of solution | ppb |
3.1 Molarity
3.2 Molality
3.3 Normality
3.4 ppm and ppb
Fig. 3 – Concentration Units at a Glance
4. Primary and Secondary Standard Substances
4.1 Primary Standard
Desirable Properties
- Very high purity.
- Stable in air.
- Not appreciably hygroscopic or volatile.
- Relatively high equivalent or molar mass.
- Readily soluble in the chosen solvent.
- Reacts rapidly and stoichiometrically.
4.2 Secondary Standard
| Feature | Primary Standard | Secondary Standard |
|---|---|---|
| Purity/stability | Very high and reliable | May change on storage or preparation |
| Preparation | Can be prepared directly to known concentration | Must be standardized |
| Role | Reference substance | Working titrant or solution |
| Examples often used in teaching | Oxalic acid, sodium carbonate, potassium hydrogen phthalate depending on application | NaOH, HCl, KMnO₄ solutions often require standardization |
Fig. 4 – Standardization Concept
5. Law of Equivalence and Normality Equation
Since number of equivalents in a solution is proportional to normality × volume:
When both volumes are expressed in the same unit, this relationship is especially useful for acid–base and redox titration calculations.
N₁V₁ = N₂V₂
0.100 × 25.0 = N₂ × 20.0
N₂ = 0.125 N
Fig. 5 – Law of Equivalence
6. Titration
Important Terms
Titrant
The standard solution delivered, usually from a burette.
Analyte
The solution whose concentration or amount is being determined.
Equivalence Point
The theoretical point at which stoichiometrically equivalent amounts have reacted.
End Point
The experimentally observed signal used to stop the titration, often a colour change.
Fig. 6 – Standard Titration Apparatus
Basic Procedure
- Rinse and fill the burette with the titrant.
- Measure a known volume of analyte using a pipette.
- Transfer the analyte to a conical flask.
- Add a suitable indicator when required by the method.
- Add titrant gradually while swirling the flask.
- Near the end point, add titrant dropwise.
- Record initial and final burette readings.
- Repeat until concordant titres are obtained.
7. Acid–Base Titration
Acid–base titration is based on a neutralization reaction between an acid and a base.
For calculations using normality at equivalence:
NHCl × 20.0 = 0.080 × 25.0
NHCl = 2.00 ÷ 20.0
NHCl = 0.100 N
Fig. 7 – Acid–Base Titration Concept
8. Redox Titration
Equivalent weight and normality in redox reactions depend on the n-factor, which is related to the number of electrons transferred in the balanced reaction.
Fig. 8 – Redox Titration: Electron-Transfer Concept
9. Important Numerical Patterns
9.1 Equivalent Weight of an Acid
Molar mass = 98
Basicity = 3
Equivalent weight = 98 ÷ 3
≈ 32.67 g eq⁻¹
9.2 Normality from Mass
Equivalent weight of H2SO4 = 49 g eq⁻¹
Number of equivalents = 4.9 ÷ 49 = 0.1 eq
Volume = 0.500 L
N = 0.1 ÷ 0.500
N = 0.20 N
9.3 Molarity from Mass
Molar mass NaCl ≈ 58.5 g mol⁻¹
Moles = 5.85 ÷ 58.5 = 0.100 mol
Volume = 0.500 L
M = 0.100 ÷ 0.500
M = 0.200 M
9.4 Titration Using N₁V₁ = N₂V₂
Nacid × 25.0 = 0.150 × 20.0
Nacid = 3.00 ÷ 25.0
Nacid = 0.120 N
9.5 Molarity to Normality
n-factor = 2
N = M × n-factor
N = 0.25 × 2
N = 0.50 N
Fig. 9 – Numerical Problem Solving Flow
10. Common Mistakes to Avoid
- Confusing molarity with molality.
- Using molar mass where equivalent weight is required.
- Forgetting that n-factor can depend on the reaction.
- Mixing mL and L without conversion in molarity or normality formulas.
- Using an unbalanced redox equation to determine electron change.
- Confusing end point with the exact theoretical equivalence point.
- Reading a burette scale in the wrong direction.
- Using a single rough titre instead of concordant titration readings.
11. Quick Revision & Exam Points
- Define gravimetric analysis and volumetric analysis.
- Define equivalent weight and derive its relation with atomic weight and valency.
- Calculate equivalent weight of acids, bases, salts and redox agents.
- Define molarity, molality, normality, formality, ppm and ppb.
- Differentiate molarity and molality.
- State the relationship between molarity and normality.
- Define primary and secondary standard substances.
- State and explain the law of equivalence.
- Derive or apply the normality equation N₁V₁ = N₂V₂.
- Define titration, titrant, analyte, equivalence point and end point.
- Explain acid–base titration.
- Explain redox titration.
- Solve numerical problems involving concentration, equivalent weight and titration.
One-Minute Revision
- Volumetric analysis uses reacting solution volume.
- Element Eq. wt. = atomic weight / valency.
- Acid Eq. wt. = molar mass / basicity.
- Base Eq. wt. = molar mass / acidity.
- Redox Eq. wt. = molar mass / n-factor.
- M = moles / litre of solution.
- m = moles / kg of solvent.
- N = equivalents / litre of solution.
- N = M × n-factor.
- Primary standard can prepare an accurately known solution directly.
- Secondary standard must be standardized.
- At equivalence: N₁V₁ = N₂V₂.
- Acid–base titration is based on neutralization.
- Redox titration is based on electron transfer.
Source handling: The original Nepal eNotes Volumetric Analysis PDF is embedded at the top using the exact Google Drive file linked by the Nepal eNotes chapter page. The typed notes follow the verified NEB Grade 12 Chemistry Unit 1 scope and are written as a searchable, responsive study companion. Because the Drive viewer does not expose the handwritten page text as readable document text here, the typed section is not presented as a word-for-word transcription.
Discussion
Share a helpful question, idea, or explanation with other students.