Laboratory Experiments of B.Sc. II Sem BT/FS/CBZ - Experiment: 6

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

 

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

 

Experiment: 6

Objective:

Study of Ionic Equilibrium by pH Measurement

Theory / Principle:

The pH of a solution depends on the degree of ionization of the solute and the nature of its components:

• Strong acids like HCl ionize completely → low pH
• Weak acids like acetic acid ionize partially → moderate pH
• Salts of weak acids and strong bases (e.g., CH₃COONa) undergo hydrolysis, leading to a basic pH
• Buffer solutions resist changes in pH and maintain near-constant values

The pH meter is used to measure the pH values accurately.

Materials Required:

Chemicals	Apparatus
0.1 M HCl (strong acid)	pH meter with glass electrode
0.1 M CH₃COOH (weak acid)	Beakers (100 mL)
0.1 M CH₃COONa (salt)	Wash bottle with distilled water
Buffer solution (CH₃COOH + CH₃COONa)	Stirring rod
Distilled water	Measuring cylinders

 

Procedure:

1. Standardize the pH meter using buffer solutions of known pH (4, 7, and 9.2).
2. Rinse the electrode with distilled water and blot dry.
3. Pour 50 mL of each test solution (HCl, CH₃COOH, CH₃COONa, buffer) into separate beakers.
4. Dip the electrode into the first solution and note the pH after stabilization.
5. Wash the electrode and repeat for each solution.
6. Record all readings carefully.

Observation Table:

Solution	Nature	Expected pH	Observed pH
0.1 M HCl	Strong acid	~1
0.1 M CH₃COOH	Weak acid	~3
0.1 M CH₃COONa	Salt of weak acid + strong base	~8
CH₃COOH + CH₃COONa buffer	Acidic buffer	~4.5–5

 

Result:

The pH values of different types of solutions were measured and found to vary according to their ionic equilibrium and nature (acidic, basic, or buffer).

• Strong acids show low pH due to complete ionization.
• Weak acids show moderate pH due to partial ionization.
• Salts may be basic if hydrolysis occurs.
• Buffer solutions maintain nearly constant pH.

Precautions:

• Calibrate the pH meter before use.
• Rinse the electrode before each measurement.
• Avoid touching the electrode tip.
• Do not stir too vigorously; avoid bubbles.
• Handle acids and chemicals with care.