CHEM 201 Lecture 27: Chem 201 General Unknown Lab Report
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Rebecca Tsarofski
Chem 201-14
4/11/19
General Unknown Lab Report
Unknown #: 43277
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Results
Ions Present Ions Absent
Cr³⁺ Al³⁺
Fe³⁺ Mn²⁺
Ni²⁺ Co²⁺
Cu²⁺ Ba²⁺
Ca²⁺
Mg²⁺
Ag⁺
Discussion
Cr³⁺
My original unknown solution was a dark gray/blue color, which could be a hint that it
contained Chromium. Starting with a light yellow solution containing smaller flakes at the
bottom, I added 3M Nitric Acid and proceeded to heat the test tubes. After adding a few drops of
cold DI water, the solution became slightly thinner. I added ten drops ether and one drop of 6%
Hydrogen Peroxide, mixed it all up, and waited a few minutes. A thin layer of blue formed on top
of the yellow solution, indicating the presence of Cr³⁺.
Cr₂O₇²⁻ (aq) + 4H₂O₂ (aq) + 2H⁺ (aq) → 2CrO(O₂)₂ (ether) + 5H₂O (l)
from HCl blue
Fe³⁺
I began with a thick brown sludge at the bottom of my test tube. Following the procedure,
I added twenty drops of 2M H₂SO₄ and heated the mixture for a few minutes. I put in another
drop of 6% Hydrogen Peroxide and five drops of DI water. I split the resulting solution into two
equal portions. To test the presence of Iron (III), I dropped 2 drops of 0.2M KSCN and a blood
red top layer formed - suggesting Fe³⁺ was present!
Fe³⁺ (aq) + 6KSCN (aq) → Fe(SCN)₆³⁻ (aq) + 6K⁺ (s)
red
Ni²⁺