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Unit 4 of 4 · B.Sc MLS Sem 1

Unit 4: Volumetric analysis

Basics of Biochemistry notes · PTU syllabus (BMLS103-18)

3 min read4 topics9 exam questions
On this page
  1. Unit summary
  2. Normal and molar solutions
  3. Standard solutions and titration
  4. Preparation of reagents
  5. Storage of chemicals
  6. Key terms
  7. Quick revision
  8. Important questions

Unit summary

Volumetric analysis determines concentrations by titrating against standard solutions. This unit covers normal and molar solutions, standard solutions, preparation of reagents and storage of chemicals.

After this unit you can

  • Prepare normal and molar solutions
  • Distinguish primary and secondary standards
  • Prepare and label reagents correctly
  • Store chemicals safely

PTU syllabus topics

  • Normal and molar solutions
  • standard solutions
  • preparation of reagents
  • storage of chemicals
ProcessPreparing a standard solution
  1. 1

    Calculate the mass needed

  2. 2

    Weigh accurately

    Analytical balance

  3. 3

    Dissolve in a little distilled water

  4. 4

    Transfer to a volumetric flask

  5. 5

    Make up to the mark

  6. 6

    Mix, label and store

1

Topic 1

Normal and molar solutions

  • A 1 N solution has one gram equivalent per litre; a 1 M solution has one mole per litre.
ProcessPreparing a solution
  1. 1

    Calculate the mass (grams = N × equivalent weight × volume in litres)

  2. 2

    Weigh accurately on the analytical balance

  3. 3

    Dissolve in a little distilled water in a beaker

  4. 4

    Transfer quantitatively to a volumetric flask with rinsings

  5. 5

    Make up to the mark, stopper and mix

  6. 6

    Label and store

Example

0.2 N HCl from concentrated HCl (about 11.6 N, 36% w/w, density 1.18): V1N1 = V2N2 → V1 = (1,000 × 0.2) ÷ 11.6 ≈ 17.2 mL diluted to 1 litre.

Key formulasDilution

  • Dilution formula

    N1V1 = N2V2 (or M1V1 = M2V2)

  • Normality of concentrated acid

    N = (density × % w/w × 10) ÷ equivalent weight

2

Topic 2

Standard solutions and titration

ComparisonPrimary and secondary standards
Primary standard
Secondary standard

Definition

Pure, stable substance whose solution is made by direct weighing

Solution whose strength is found by titrating against a primary standard

Properties

High purity, non-hygroscopic, stable, high equivalent weight

May absorb moisture or CO₂

Examples

Anhydrous sodium carbonate, oxalic acid, potassium dichromate, potassium hydrogen phthalate

NaOH, HCl, KMnO₄

ProcessStandardising NaOH
  1. 1Prepare approximate 0.1 N NaOH
  2. 2Titrate against 0.1 N oxalic acid (primary standard) with phenolphthalein
  3. 3End point: faint permanent pink
  4. 4Calculate N(NaOH) = N(oxalic) × V(oxalic) ÷ V(NaOH)
  5. 5Record the factor on the label
  • Indicators: phenolphthalein (8.3–10, colourless to pink) for strong base titrations; methyl orange (3.1–4.4, red to yellow) for strong acid with weak base.
3

Topic 3

Preparation of reagents

Key termsGood practice
Grade
Use analytical reagent (AR) grade chemicals
Water
Distilled or deionised water
Accuracy
Calibrated balance and volumetric glassware
Labelling
Name, concentration, date of preparation, expiry, preparer's initials, hazard symbols
Records
Reagent register with lot numbers
Verification
Check new reagents with controls before use
4

Topic 4

Storage of chemicals

ComparisonStorage rules
Requirement
Examples

Flammables

Fire-proof cabinet, away from heat and oxidisers

Ether, alcohol, acetone

Corrosives

Low shelves, secondary containers; acids apart from bases

HCl, H₂SO₄, NaOH

Oxidisers

Away from organics and flammables

Potassium permanganate, nitric acid

Light-sensitive

Amber bottles

Silver nitrate, hydrogen peroxide

Hygroscopic

Tightly closed, desiccator

NaOH pellets, calcium chloride

Toxic

Locked cabinet; register

Cyanides, mercury salts

Temperature-sensitive

Refrigerator (2–8 °C)

Enzymes, kits, standards

  • Store alphabetically only within compatible groups; keep MSDS available; first-in, first-out; discard expired chemicals as hazardous waste.

Key terms

Standard solution
Solution of accurately known concentration
Primary standard
Pure substance used to prepare a standard by direct weighing
Titration
Adding a solution of known strength to find another's concentration
End point
Point where the indicator changes colour
Hygroscopic
Absorbing moisture from air

Quick revision

  • Grams = N × eq. wt × litres; preparation steps; N1V1 = N2V2.
  • Primary vs secondary standards; standardising NaOH with oxalic acid.
  • Indicators: phenolphthalein, methyl orange.
  • Reagent preparation and labelling.
  • Storage of flammable, corrosive, oxidising, light-sensitive, hygroscopic and toxic chemicals.

Important exam questions

Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).

Short-answer questions

  1. Q1.How much Na₂CO₃ is needed for 250 mL of 0.1 N solution?
  2. Q2.What is a primary standard?
  3. Q3.Why can NaOH not be a primary standard?
  4. Q4.State the dilution formula.
  5. Q5.What should a reagent label contain?
  6. Q6.How should flammable chemicals be stored?

Long-answer questions

  1. Q1.Describe the preparation of normal and molar solutions with examples.
  2. Q2.Explain primary and secondary standards and standardisation by titration.
  3. Q3.Describe the preparation of reagents and storage of chemicals.

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