into the rose tint. Calculate the ml.'s of the acid equivalent to 100 ml. 

 of the NaOH, 



4) IN Citric Acid. (H3CgH507* H2O) ... Dissolve 35 g. of the Merck reagent 

 crystals in enough distilled water to make 500 ml. Standardize against the 

 l.OOON NaOH exactly as with the phosphoric acid, taking the same end-point. 

 Store in the refrigerator. 



5) Boric Acid Crystals. (H3BO3 ) . . . Dry Merck's reagent grade in thin 

 layers over CaCl 2 in a desiccator. 



Stock Solution: 



Using a burette, measure into a 1 liter volumetric flask the volumes 

 of phosphoric acid solution (3) and citric acid solution (4) equivalent 

 to 100.0 ml. of the IN NaOH, as determined by the titrations. Add 343.0 

 ml. of IN NaOH and 3.54 g. of the Boric Acid and dilute to the mark with 

 distilled water. 



Buffers : 



To make 100 ml. of buffer at the ionic concentrations given above, pi- 

 pette 20 ml. of stock solution into a 100 ml. volumetric flask, add the 

 specified volume of O.IOOON HCl as given in the table below, and dilute 

 to the mark with distilled water. 



ml. of O.IOOON HCl 

 pH 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 



2 73.30 70.35 67.85 65.70 63.85 62.25 60.80 59.55 58.45 57.40 



3 56.50 55.70 54.95 54.30 53.70 53.20 52.65 52.10 51.55 51.02 



4 50.50 49.97 49.45 48.91 48.35 47.80 47.26 46.75 46.22 45.68 



5 45.18 44.60 44.05 43.50 42.94 42.36 41.80 41.23 40.61 40.00 



6 39.42 38.94 38.09 37.45 36.74 36.06 35.36 34.65 33.92 33.25 



7 32.65 31.98 31.45 30.83 30.35 29.87 29.43 29.05 28.68 28.33 



8 28.02 27.69 27.45 27.25 26.90 26.60 26.10 25.63 24.90 24.33 



9 23.75 23.05 22.38 21.72 21.12 20.52 19.94 19.37 18.81 18.35 



10 17.92 17.43 16.97 16.64 16.36 16.15 15.95 15.70 15.40 15.02 



11 14.52 13.93 13.20 12.30 11.23 10.00 8.40 6.60 4.70 2.06 



12 0.40 



•49- 



