Aim of Experiment: To systematically analyze cations in a known sample.
Materials Used:
Beaker, test tubes, flask, centrifuge, dropper, water bath, spatula
Chemical Used: copper ions (Cu2+), nickel ion(Ni2+) , cobalt ion (Co2+), zinc ion (Zn2+),
iron ion (Fe3+), chromium ion (Cr3+) and manganese ion (Mn2+) Sodium hydroxide
(NaOH), hydrogen peroxide (H2O2), ammonium hydroxide (NH4OH), barium chloride
(BaCl2), sodium bismuthate (NaBiO3), nitric acid (HNO3), hydrochloric acid (HCl),
dimethylglyoxime (DMG), sulfuric acid (H2SO4), ammonium thiocyanate (NH4SCN),
potassium cyanate( KSCN), potassium ferrocyanide (K4Fe(CN)6) and distilled water.
Formula Used:
1mL = 20drops
Procedure:
Reactions with NaOH: Seven test tubes were cleaned and rinsed. The test tubes were then
labeled with the cation names listed above. 1mL of 0.1M of the cation solutions were
measured into their corresponding test tubes. Each color change was observed and
recorded. About 10mL of 6M NaOH was poured into a clean beaker. One drop of this
solution was added to the first test tube. The test tube was shaken and the color was
observed and recorded. A few drops of NaOH was added again and observed for changes.
Drops of NaOH were continuously added until about 20 drops and the final observation
was recorded. Then 6M of NaOH was added in a dropwise fashion to the other six cation
samples. The observations were recorded and all test tubes were retained for further use.
Oxidation with H2O2:
A 250mL was half filled with water and then heated to boiling point was used as a
boiling water bath. Meanwhile about 10 drops of 3% H2O2, an oxidizing agent, was
added to each of the seven tubes from part A, mixed thoroughly and the observations
were recorded. Out of the seven cations, only Cr3+ and Mn2+ were saved, the rest were
emptied and their test tubes were cleaned.
Test for Manganese:
10 more drops of H2O2 were added to the manganese test tube. Then it was gently and
frequently shaken. After signs of fizzing have stopped, the test tube was centrifuged to
separate the dark precipitate from the clear liquid. The clear portion of the centrifuged
solution was decanted and discarded as much as possible. The precipitate was then
washed by adding 3-5 ml of distilled water with shaking and then centrifuged again.
Without disturbing the liquid or solid contents of the test tube, several pepper granule
size grains of NaBiO3 was gently added using a tip of a spatula. The solution was
observed for signs of small pink- red ”streamers” of color near the NaBiO3 particles in
the undisturbed test tube. The presence of this color small pink- red streamer” indicated
the presence of Mn2+.
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Results
Catio Reage Observati
n
nt
on after
Added first 1
drop/
Observati
on after
20 drops
Soluti
on
added
Mn2+
NaOH
Same
H2O2
Cr3+
NaOH
Clear
green
H2O2
Clear
yellow
NH4OH
Ni2+
NaOH
same
H2O2
same
NaOH
same
H2O2
Dirty
brown
NH4OH/
dimethylglyox
ime
(DMG)
NH4OH/
H2SO4
Strawberr
y-red
precipitate
Co2+
Fe3+
NaOH
Light
brown
and
cloudy
Cloudy
greenish
blue
Light
green
Precipitat
e
Precipitat
e with
blue
Deep
orange
Precipitat
e present
H2O2
same
Cu2+
NaOH
Precipitat
e, light
blue
Deep
blue
H2O2
1. NH4OH/
KSCN
2. NH4OH/
K4Fe(CN)6
NH4OH/
Acetic acid
Zn2+
NaOH
White
Precipitat
e
Precipitat
e
dissolved
and clear
H2O2
Clear in
the middle
and blue at
the top
K4Fe(CN)6
bottom
clear
NH4OH/ HCl /
K4Fe(CN)6
1.Red
color
2. Blue
precipitate
Blue color
disappeare
d
Red
precipitate
Zn3K2
[Fe(CN)6]
2 Grayblue
precipitate
Observati Solution added Observati
ons
ons
After
addition of
H2O2
Brown
NH4OH/
with
precipitate
Light Pink
Color
Conclusion:
The experiment was performed meticulously and the final observation corresponded with
the desired observation. There was no errors noted and the experiment was a success. A
real life application will be to differentiate the chemical composition in table salt.
Post Lab Questions:
2.
Cation
Oxidation Formula
Reduction Formula
3
Zn2+
Zn3K2 [Fe(CN)6]
2+
Cu
Cu2Fe(CN)6
Fe3+
K4Fe(CN)6
2+
Ni
Mn2+
Co2+
Zn2+ + K4Fe(CN)6  Zn3K2 [Fe(CN)6] (Reduction Reaction)
Zn2+ + 2e  Zn Zinc ion was reduced to Zinc element
Cu2+ + K4Fe(CN)6  Cu2Fe(CN)6 (Reduction Reaction)
Cu2+ + 2e  Cu
Copper ion was reduced to copper element
3+
Fe + K4Fe(CN)6 K4Fe(CN)6 (Reduction Reaction)
2. If my original cation solution is colorless, I will conclude that my cation is zinc
because it the only ion among the seven that will be colorless when NaOH and NH4OH
are present.
3. If an unknown solution was treated with excess NaOH and then with 3% H2O2 and
then that cation was centrifuged, the cation that may be present in the precipitate are Fe3+,
Co2+, Mn2+ and Ni2+. The decanted portion may contain Zn2+ and Cr3+.
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