An Improved QualitativeAnalysis Procedure for Aluminum Subgroup Cations C. R. Kisiner and Patricia J. Robinson University of Wisconsin-La Crosse, La Crosse. WI 54601 The traditional procedures for the analyses of Al" and CCP+ in inoreanic aualitative analvsis schemes have frustrated hoth the sludent nnd teachw since in(oncluaive and or false test result.. art. d i m ohrer\ed. \Vhm ('r3- is rrrezent. it trru~~entlv fails to give a confirming test, while ~1:': may be inco&ect& reported as being present. Most qualitative analysis schemes (1-4) include APC and Cr:If, which are separated into the same suhgroup with Zn2+ by dissolving, in a nitric acid solution, a precipitate of insoluble sulfides and ammonia-insoluble hydroxides. With the addition of solutions of NaOH and Ha02, C r o p - , Al(OHL-, and Zn(0H)i'- are separated from other metal ions that form insoluble hydroxides.
solution obtained from this separation, and it may he separated from the C r 0 2 and confirmed using any of the previously reported procedures (1-4). Flow Diagram- Aluminum Subgroup
Cr,O,'-, All*, Zn"
CrO., AI3+,Zn" blue
T h e solution containing these aluminum subgroup ions is acidified to yield Al:'+, Cr20i2-, and Zn'+ in solution, and, on adding NH:j until basic, AKOH):] is separated from Cr0i2- and Zn(NH:i)iHf. At this point, if chromium(II1) was present in the original solution but not completely oxidized to Cr0i'-, the precipitate, which is expected to he the clear gelatinous AI(0Hh. mav aooear .. dark due to the oresence of C r ( O H L The discoloration is not removed by suc~essivewashings, and the student is inclined to reoort incorrect results for an Al:'+
I
