PRACTICE I. 

 PREPARATION OF A STANDARD HYDROCHLORIC ACID SOLUTION.* 



By the use of a hydrometer and specific gravity tables prepare five 

 liters or more of approximately one-half normal hydrochloric acid, using 

 chemically pure concentrated acid and ammonia-free water. 



Standardize by the silver nitrate method : Place exactly 25 cc. (note 

 temperature of stock solution when measured out) of the acid solution, 

 measured with a pipette, in a 300 cc. Erlenmeyer flask, dilute to 75 cc., add 

 at once from a burette sufficient $% silver nitrate solution to nearly, but 

 not quite, precipitate all the chlorin. Close the flask with a clean rubber 

 stopper and shake till the precipitate will settle nearly completely in a short 

 time. Then add the silver nitrate in i cc. portions, shaking after each 

 addition, until the precipitation is complete, avoiding more than I cc. ex- 

 cess of silver nitrate solution. 



Shake until the silver chlorid settles well, wash three times by decanta- 

 tion (after shaking each time) using about 100 cc. of water containing I cc. 

 concentrated nitric acid per liter and decanting the liquid through a 9 cm. 

 filter. Transfer the precipitate to the filter, dry, transfer the bulk of the 

 precipitate to a watch-glass or crucible, and burn the paper in a weighed 

 crucible. Add 2 to 5 drops of concentrated nitric acid to dissolve reduced 

 silver and then 2 to 5 drops of concentrated hydrochloric acid. Evaporate 

 to dryness without spattering, add the main precipitate, dry to con- 

 stant weight at I20 9 to 130, cool in a desiccator, and weigh. 



Record the weights of silver chlorid from duplicate 25 cc. portions of 

 the standard hydrochloric acid. 



*To be done by the instructor. 



