14 GENERAL METHODS 



To determine the exact value of the solution it is only necessary 

 to find out how much of it is required for the neutralization of a 

 known volume of the .5 N oxalic acid solution. With a dry and 

 clean pipette transfer 25 c.c. of the oxalic acid into a beaker or 

 flask. Dilute it by adding 100 to 150 c.c. of water, and add two 

 drops of the indicator (1 per cent alcoholic solution of phenol- 

 phthalein). 



Fill a dry, clean burette with the alkali and cover with a 

 test-tube. After adjusting the solution in the burette to the zero 

 mark, run it into the diluted oxalic acid, more and more cautiously 

 toward the end until finally one single drop produces a deep red 

 coloration. Note the volume of alkali required (to within .05 

 c.c.). Repeat the titration until two successive ones give exactly 

 the same figure. 



In titrating acids and alkalies the alkali must always be run into 

 the acid solution, not vice versa. 



From the result obtained calculate how much of the alkali 

 would be required to neutralize 1 liter of the oxalic acid solution. 

 By means of a 100 c.c. pipette and a burette, transfer the required 

 amount of the alkali to the liter measuring flask, and fill up to the 

 mark with water. Mix, transfer to a dry bottle, label, and stopper 

 with a rubber stopper. 



As a check on the work determine the concentration of an 

 unknown hydrochloric acid solution (furnished), using as indicator 

 (a) phenolphthalein, (6) alizarin red (2 drops 1 per cent aqueous 

 solution). 



3. Half Normal Hydrochloric Acid. Concentrated hydro- 

 chloric acid is approximately 10 N solution of HC1. From it 

 prepare 1000 c.c., .5 N solution, using the half normal sodium 

 hydroxide as a standard and alizarin red as indicator. The 

 most convenient way is first to prepare 1200 to 1300 c.c. of a 

 solution somewhat stronger than half normal, and then, on the 

 basis of titrations with the standard alkali, to dilute the required 

 amount with water to 1 liter. One liter of half normal hydrochloric 

 acid is enough for all the analytical work described in this manual. 



Those who have had experience in volumetric analysis may use 

 simply standardized solutions instead of the half normal in the 

 case of hydrochloric acid and in the case of all other standard 

 solutions, but beginners should not omit the preparation of a 

 strictly half normal acid. 



