PRACTICE I 



PREPARATION OF STANDARD HYDROCHLORIC ACID 



SOLUTION i 



By th'e use of a hydrometer and the specific-gravity table prepare 

 5 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., and add at once from a burette sufficient 5 per cent 

 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 almost completely in a short time. Then 

 add the silver nitrate in 1-cc. portions, shaking after each addition, 

 until the precipitation is complete, avoiding more than 1 cc. excess 

 of silver nitrate solution. 



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

 decantation (after shaking each time), using about 100 cc. of water 

 containing 1 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 add 2 to 

 5 drops of concentrated hydrochloric acid. Evaporate to dryness 

 without spattering, add the main precipitate, dry to constant weight 

 at 120 to 130, cool in a desiccator, and weigh. 



Kecord the weights of silver chlorid from duplicate 25-cc. portions 

 of the standard hydrochloric acid. 



1 To be done by the instructor. 



