Weigh out 105.055 g. of dry, crystalline Citric Acid (CoHgCU»H20) 

 and dissolve in enough water to make 1 liter. Merck Reagent grade should 

 be used, and it is satisfactory to use a bottle opened and kept in the 

 dry room. To be sure of the molarity, titrate with l.OOOM NaOH. The 

 end-point is a distinct red color of the phenolphthalein indicator. 



Bu f f e r s : 



To make 250 ml. of . I M Citrate Buffer, pipette 50 ml. of the 

 0.500M stock into a 250 ml. volumetric flask. Add the number of ml. of 

 l.OOON NaOH indicated below and dilute to the mark with distilled water, 



pH ml. l.OOONaOH 



2.2 2.23 



2.4 4.63 



2.6 7.13 



2.8 10.10 



3.0 13.40 



3.2 17.10 



3.4 20,50 



3.6 23.93 



3.8 26.00 



4.0 29.50 



■41- 



