aiAPTER VII. 

 BUFFERS 



Each taole here given is for preparing a given volume of buffer, con- 

 taining a specified concentration of the desired buffer anion, at the various 

 pH's listed. These volumes and concentrations are given above each table. 

 For each specie of buffer, two solutions are needed; a standard stock solu- 

 tion of some salt of the buffer anion, and a solution of either standard 

 acid or alkali, usually NaOH or HCl . Instructions for making up the stock 

 solutions are given above each table of buffers. A given volume of this 

 stock is pipetted into a flask, the required amount of standard acid or 

 alkali buretted into the same flask, and this mixture then diluted to the 

 proper volume with distilled water, using a volumetric flask. This will 

 give the listed volume of buffer at the specified anion concentration and 

 at exactly the pH listed. If smaller or larger volumes are desired, the 

 amounts of stock solution and standard alkali or acid should be altered 

 proportionally. If an anion concentration other than that specified is 

 desired, one alters the amounts of stock solution and standard acid or 

 base proportionally, but does not change the total volume upon dilution. 

 This will not significantly alter the pH, provided that the anion con- 

 centration is somewhere between 1/4 X and 2X that specified in the table. 

 Within this range, the effects of dilution on the pH of buffers is negli- 

 gible. In all cases, remember that the important factor is the ratio of 

 stock anion solution to standard acid or base solution. As long as one 

 maintains the proportions of these two solutions to each other, the buffer 

 will have the proper pH. 



In making up the stock anion solutions, it is always necessary to use 

 the Merck Reagent Grade or Baker's Analyzed Grade chemical. If these 

 bottles are initially opened in the dry room and kept in that room at low 

 humidity at all times, the chemicals may generally be used directly with- 

 out drying. For high accuracy, however, (i.e. in making standard buffers), 

 the salts must be treated as directed and dried in an oven. 



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