Laboratory Experiments of B.Sc. II Sem BT/FS/CBZ - Experiment: 4

  Laboratory Experiments of B.Sc. II Sem BT/FS/CBZ

 

Dr. Navdeep Sharma
Institute of Sciences
SAGE University, Indore (M.P.)

 

Experiment: 4


Objective:

    To prepare an acidic buffer and a basic buffer solution and to study their ability to resist changes in pH upon addition of small amounts of acid or base.

Materials Required:

For Acidic Buffer (Acetic Acid + Sodium Acetate):

  • Glacial acetic acid (CH₃COOH) – 5 mL
  • Sodium acetate (CH₃COONa) – 4 g
  • Distilled water – up to 100 mL

For Basic Buffer (Ammonium Hydroxide + Ammonium Chloride):

  • Ammonium hydroxide (NH₄OH) – 5 mL
  • Ammonium chloride (NH₄Cl) – 5 g
  • Distilled water – up to 100 mL

General Apparatus:

  • Measuring cylinder
  • Beakers (100 mL)
  • Volumetric flask (100 mL)
  • Glass rod
  • Dropper
  • pH meter or universal pH paper

Theory:

A buffer solution is one that resists changes in pH when small quantities of acid or base are added.

  • An acidic buffer contains a weak acid and its salt with a strong base.
  • A basic buffer contains a weak base and its salt with a strong acid.

Procedure:

A. Preparation of Acidic Buffer (pH ≈ 4.75)

  1. Take 5 mL of glacial acetic acid in a beaker.
  2. Add 4 g of sodium acetate to the solution.
  3. Mix well using a glass rod until the salt dissolves.
  4. Transfer the solution to a 100 mL volumetric flask.
  5. Make up the volume to 100 mL with distilled water.
  6. Measure the pH using a pH meter or pH paper (should be around 4.7–5.0).

B. Preparation of Basic Buffer (pH ≈ 9.25)

  1. Take 5 mL of ammonium hydroxide in a beaker.
  2. Add 5 g of ammonium chloride to it.
  3. Stir well until the salt dissolves completely.
  4. Transfer the solution to a 100 mL volumetric flask.
  5. Make up the volume to 100 mL with distilled water.
  6. Measure the pH using a pH meter or pH paper (should be around 9–9.5).

Observation:

  • The acidic buffer shows little change in pH on adding a small amount of HCl or NaOH.
  • The basic buffer similarly resists change in pH upon addition of a small amount of acid or base.

Result:

  • Both acidic and basic buffer solutions were successfully prepared.
  • They demonstrated buffering capacity by resisting change in pH upon addition of acid/base.

Precautions:

  • Use freshly prepared reagents and clean glassware.
  • Measure liquids carefully using a measuring cylinder or pipette.
  • Stir solutions thoroughly for proper mixing.
  • Calibrate the pH meter before use if available.

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