BACKGROUND
Buffer Solutions
Buffer solution is a type of solution which is used for keeping the pH at approximately constant value for using it in a number of chemical reactions.
So, the basic objective of this test is to prepare buffer solutions and measuring the pH of this buffer solutions.
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REQUIREMENTS
Reagents:
- Acetic Acid 0.2 M: Glacial acetic acid 1.5 ml is made upto 100 ml by using distilled water.
- Sodium Acetate Solution: 0.64 gm of sodium acetate + 100 ml distilled water
- Diethyl barbituric acid
- Sodium diethyl barbititrate
- Citric acid: citric acid 2.10 gm +100 ml distilled water.
- Sodium citrate solution 0.1 M: sodium citrate 2.94 gm +100ml distilled water.
- Sodium carbonate solution 0.2 M:2.12 gm anhydrous sodium carbonate +distilled water (100 ml).
- Sodium bicarbonate solution: Sodium bicarbonate 1.68 gm + 100 ml distilled water.
- Monobasic sodium phosphate: 2.78 gm sodium dihydrogen phosphate + 100 ml distilled water.
- Dibasic sodium phosphate: 5.3 gm of disodium hydrogen phosphate +100 ml distilled water.
Apparatus:
- Conical flask
- Pipette
- pH meter
PROCEDURE
Acetic acid-sodium acetate buffer1
Take a 100 ml flask and to it 36.2 ml of sodium acetate solution through a pipette and then to it add 14.8 ml glacial acetic acid. With the help of distilled water make the total volume 100 ml. The resultant is 0.2 M of acetic acid-sodium acetate buffer. The pH is measured with the help of a pH meter. The electrode is washed with distilled water and then it is dipped in the prepared buffer solution. The resultant pH is 4.6.
Barbitone buffer
Mix 2.85 gm of diethyl barbituric acid and 14.2 gm of sodium diethyl barbititrate in distilled water and then make the final volume 1000 ml. This is Barbitone buffer. The pH is measured with the help of pH meter and the final pH comes out as 6.8.
Citrate buffer1
Mix 46.5 ml of citric acid with 3.5 ml of sodium citrate solution and make the final volume 100 ml with the help of distilled water. This is 0.1 M citrate buffer. The pH of this buffer is measured with the help of a pH meter and the pH is 2.5.
Carbonate-Bicarbonate buffer
In a flask take 27.5 ml of sodium carbonate solution and to it add 22.5 ml sodium bicarbonate solution. Then make the total volume 100 ml with the help of distilled water. This is 0.2 M carbonate-Bicarbonate buffer. The pH meter is standardized and the pH of the prepared buffer solution is measured. The pH is 10.2
Phosphate buffer
Dihydrogen sodium phosphate (39 ml) is mixed with disodium hydrogen phosphate (61 ml) and the final volume is made to 200ml with distilled water.2 This solution results in 0.2 M of phosphate buffer. The pH of phosphate buffer is measured with the help of pH meter and it comes out 6.8.
CONCLUSION
Correctly prepared buffer solution is highly used during various chemical reactions.
REFERENCES
- Crisostomo, A. C., et al. (2010). Laboratory Manual in General Biochemistry. Quezon City: Philippines.
- Rabara, B. P. (2012). pH Measurement and Buffer Preparation.
Also read:
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- Test for Proteins
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- Estimation of protein by Folin Lowry method
- Determination of saponification value of the given oil/fat
- Determination of saponification value of fat (coconut oil)
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