The following article will guide you about how to prepare buffers.
Substances diminishing the change in pH, which would otherwise occur in the solution, are known as buffers. Chemical reactions are almost always associated with a change in pH in a solution. Variation in pH causes change in the reaction rate or velocity of reaction. The change in pH is greatly reduced, within a range, by the addition of a given amount of an acid or base in the solution.
Buffers consist of weak acids together with their conjugate bases, that is of a solution of a weak acid with one of its salts. Examples: carbonic acid bicarbonate; di-hydrogen phosphate mono-hydrogen phosphate; acetic acid-acetate; citric acid-citrate, etc.
The acid is only slightly dissociated; in each case there is an excess of anions (base) which can accept hydrogen ions, when added. With the addition of base the un-dissociated acid can dissociate and donate hydrogen ions to the added base. The added acid or base is thus neutralized with a much small change in [H++] and pH, than would result if the same amount added to water.
Phosphate Buffer:
Prepare solutions A and B in separate volumetric flasks with double distilled water and mix them as indicated in the table to obtain desired pH.
Stock solution A:
0.2 M solution of monobasic Na-phosphate (31.2 g NaH2PO4, 2H2O in 1000 ml).
Stock solution B:
0.2 M solution of dibasic Na-phosphate (53.65 g Na2HPO4, 7H2O or 71.7 g of Na2HPO4, 12H2O in 1000 ml).
Mix x ml A + y ml B = 100 ml.
Acetic Acid-Sodium Acetate Buffer 0.2 M at 37°C :
Solution A:
0.2 M Acetic acid. Prepared by adding double-distilled water to 11.5 ml glacial acetic acid to make 1000 ml.
Solution B:
0.2 M Sodium acetate. Dissolve 16.41 g anhydrous sodium acetate (CH3COONa) or 27.22gm hydrate salt (CH3COONa, 3H2O) in double-distilled water and make to 1000 ml.
Mix x ml A + y ml B = 100 ml.
