EXPERIMENT 5 Preparation and Properties of Buffer Solution

EXPERIMENT (5) Preparation and Properties of Buffer Solution

Theory: Buffer solution: A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its salt or weak base and its salt. Buffer solutions are resistant to PH changes caused by the addition of an acid or base.

Theory: Examples of buffer solutions: Weak acid & its salt: Acetic acid & sodium acetate (CH 3 COOH) & (CH 3 COONa) CH 3 COOH CH 3 COO- + H+ CH 3 COONa CH 3 COO- + Na+ HCl + (HA + A-) 2 HA + Cl. Na. OH + (HA + A-) 2 A- + Na+ + H 2 O

Theory: Examples of buffer solutions: Weak base & its salt: Ammonia & ammonium chloride (NH 3) & (NH 4 Cl) NH 3 + H 2 O NH+4 + OH NH 4 Cl NH+4 + Cl. HCl + (BOH + B+) H 2 O + 2 B+ + Cl. Na. OH + (BOH + B+) Na+ + 2 BOH

Procedure: 1. Prepare the following four solution: Solution 1 2 3 4 0. 1 M Sodium acetate 25 25 0. 1 M Acetic acid 25 75 125 175 Total volume 50 100 150 200 2. Calculate theoretical PH value for solution. 3. Measure the PH value for each solution by using PH meter and compare the results with theoretical values.

Procedure: 4. To 25 ml of one of the above buffer solutions, add 5 drops of 0. 1 M Na. OH then measure the PH of the resulting solution. 5. To 25 ml of one of the above buffer solutions, add 5 drops of 0. 1 M HCl then measure the PH of the resulting solution. 6. Measure the PH of the distilled water. 7. To 25 ml sample of water, add 5 drops of 0. 1 M Na. OH, and to another 25 ml add 5 drops of 0. 1 M HCl then – after mixingmeasure the PH of the two solutions.

Results: Tabulate your results as following: Solution 1 2 3 4 Distilled water PH Theoretical PH Practical Effect of HCl Effect of Na. OH