Determination of the Composition of Unknown Mixtures of Metal Cations
Aidnel Geister Navarro
CHEM 203- BB6
Melissa Obert
13 October 2011
ABSTRACT
The unknown mixture, mixture 11, contained the cations Ba2+, Mn2+ and Zn2+.
RESULTS
Upon receiving unknown mixture 11, I used a Pasteur pipette to fill 1 row of wells with 2
drops (~200 µL) of the mixture per well. I added 1 drop (~100 μL) of 3 M HCl in well 1 (figure
2), 3 M H2SO4 in well 2 (figure 3), 0.1 M Na3PO4 in well 3 (figure 4), 0.1 M Na2CO3 in well 4
(figure 5), 0.1 M K2CrO4 in well 5 (figure 6), 3 M NaOH in well 6 (figure 7), 3 M NH3 in well 7
(figure 8), 0.1 M KSCN in well 8 (figure 9), 0.1 M KI in well 9 (figure 10), solid KI in well 10
(figure 11), and 0.1 M K4Fe(CN)6 in well 11 (figure 12). After dropping the 11 anion reagents
into their respective well, I added 19 M NaOH to well 6 (figure 13). In the fume hood, I then
added 15 M NH3 into well 7 (figure 13). Finally, I added 0.1 M K2S2O3 in well 9 (figure 13).
The observations and balanced net ionic equations for the reactions are listed in tables 1, 2 and 3.
DISCUSSION
The mixture of Ba2+, Mn2+ and Zn2+ was fairly easy do distinguish through the process of
elimination. The confirmation of the presence of Ba2+, Mn2+ and Zn2+ is only possible through
the process of elimination. This is because the precipitates they form are easily masked by
precipitates of other cations. Because the mixture was colorless, Cu2+ and Ni2+ were immediately
ruled out. Upon the addition of 3 M HCl into the mixture, no color change was observed and no
precipitate formed; this eliminated Ag+ which forms a white precipitate, Pb2+ which forms a
white precipitate, and Fe3+ which produces a yellow solution. With this, Cu2+, Ni2+, Ag+, Pb2+
and Fe3+ are ruled out and only Ba2+, Mn2+ and Zn2+ remain in the mixture.
APPENDIX
1. What were your initial observations of your unknown solution?
 The unknown mixture was colorless (student lab notebook page 15).
2. What was the first cation you determined not to be present in your unknown?
 Cu2+ and Ni2+ were the first cations I determined not to be in my unknown mixture
(student lab notebook page 15).
3. What was the 1st anion you added to your mixture and what were your observations of it?
 3 M HCl was the 1st anion I added to my mixture which did not result in a reaction,
leaving the mixture colorless (student lab notebook page 15).
4. What was the 4th anion you added to your mixture and what were your observations of it?
 0.1 M Na2CO3 was the 4th anion I added to my mixture, resulting in a cloudy white
precipitate (student lab notebook page 15).
5. What cations did you determine to be present in your unknown?
 I determined Ba2+, Mn2+ and Zn2+ to be present in the unknown mixture (student lab
notebook page 15).