Prepare acetate buffer of pH 4.6 to 6.0 and measure their pH using pH meter
Requirements: Wash bottle, volumetric flask, beaker, Sodium acetate, glacial acetic acid.
Requirements: Wash bottle, volumetric flask, beaker, Sodium acetate, glacial acetic acid.
Definition of pH
The hydrogen ion concentration of most solution is extremely low. pH is strictly defined as the negative logarithm of the hydrogen ion activity, but in practice the hydrogen ions concentration is usually taken and this is virtually the same as the activity except in strongly acid solution.
Measurement of pH
pH indicator: An approximate idea of the pH of a solution can be obtained using indicators. These are organic compounds of natural or synthetic origin whose colour is dependent upon the pH of the solution. Indicators are usually weak acid which dissociate in solution.
Accurate measurement of pH: The most convenient and reliable method for measuring pH is by the use of a pH meter which measure the e.m.f of a concentration cell formed form a refrence electrode, the test solution and a glass electrode sensitive to hydrogen ions.
Glass electrode: The glass electrode consists of a very thin bulb about 0.1mm thick blown on to a hard glass tube of high resistance. Inside the bulb is a solution of hydrochloric acid (0.1 mL/litre) connected to a platinum wire via a silver chloride electrode, which is reversible to hydrogen ion. A buffer solution is one that resists pH. Change on the addition of acid or alkali such solution are used in many biochemical experiment where the pH needs to be accurately controlled.
Glass electrode: The glass electrode consists of a very thin bulb about 0.1mm thick blown on to a hard glass tube of high resistance. Inside the bulb is a solution of hydrochloric acid (0.1 mL/litre) connected to a platinum wire via a silver chloride electrode, which is reversible to hydrogen ion. A buffer solution is one that resists pH. Change on the addition of acid or alkali such solution are used in many biochemical experiment where the pH needs to be accurately controlled.
From the Henderson-Hasselbalch equation the pH of a buffer solution depends on two factors. One is the pka value and other the ratio salt and acid.
Procedure for Measurement of pH
Preparation of acetate buffer pH 4.6: 5.4 gram of sodium acetate was dissolved in sufficient amount of distilled water then 2.4 mL of glacial acetic acid was added and volume was made up to hundred mL and pH was noted down using pH meter.
Preparation of acetate buffer pH 4.7: 0.84 gram of sodium acetate was dissolved in sufficient amount of distilled water then 0.33 mL of glacial acetic acid was added and volume was made upto 100mL and pH was noted down using pH meter.
Preparation of acetate buffer pH 5.0: 1.36 gram of sodium acetate was dissolved in sufficient amount of distilled water then 0.6 mL of glacial acetic acid was added and volume wad made up to 100 mL and pH was noted down using pH meter.
Preparation of acetate buffer pH 5.5: 27.2 gram of sodium acetate was dissolved in sufficient amount of distilled water then 50 mL of glacial acetic acid was added and volume was made upto 100mL and pH was noted down using pH meter.
Result: Acetate buffer solutions are prepared and submitted.
Preparation of acetate buffer pH 4.7: 0.84 gram of sodium acetate was dissolved in sufficient amount of distilled water then 0.33 mL of glacial acetic acid was added and volume was made upto 100mL and pH was noted down using pH meter.
Preparation of acetate buffer pH 5.0: 1.36 gram of sodium acetate was dissolved in sufficient amount of distilled water then 0.6 mL of glacial acetic acid was added and volume wad made up to 100 mL and pH was noted down using pH meter.
Preparation of acetate buffer pH 5.5: 27.2 gram of sodium acetate was dissolved in sufficient amount of distilled water then 50 mL of glacial acetic acid was added and volume was made upto 100mL and pH was noted down using pH meter.
Result: Acetate buffer solutions are prepared and submitted.
Prepare phosphate buffer of pH 5 and pH 7and measure their pH using pH meter
Requirement: Wash bottle, volumetric flask, and beaker, potassium dihydrogen phosphate, potassium hydroxide, Disodium hydrogen phosphate.
Phosphate
This is probably most popular buffer but phosphate readily forms complexes with heavy metal. Phosphate is also inconvenient as it plays an active part in a no. of biochemical reaction where it can act as an activator, inhibitor or metabolite. The buffering capacity above pH 7.5 is poor.
Procedure for Measurement of pH for Phosphate
Preparation of phosphate buffer (pH 5): 0.68 gram of potassium dihydrogen phosphate was dissolved in sufficient amount of distilled water and volume was made up to 100 mL then adjusts the pH to 5 with 10 M potassium hydroxide.
Preparation of phosphate buffer (pH 7): 0.050 gram of anhydrous disodium hydrogen phosphate and 0.030 gram of potassium dihydrogen phosphate was dissolved in sufficient amount of distilled water and volume was made up to 100 mL.
Result: Phosphate buffer solutions are prepared and submitted
Preparation of phosphate buffer (pH 7): 0.050 gram of anhydrous disodium hydrogen phosphate and 0.030 gram of potassium dihydrogen phosphate was dissolved in sufficient amount of distilled water and volume was made up to 100 mL.
Result: Phosphate buffer solutions are prepared and submitted
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