General unknown lab report PDF

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] Emily Tafoya Chem 201, Section 12 4/12/18 General Unknown Lab Report Unknown Number: #44280 Results: Ions Present: Fe3+, Co2+, Ni2+, Cr3+ Ions Absent: Al3+, Ba2+, Mg2+, Mn2+, Ca2+, Cu2+, Ag+

Discussion: Fe3+ -

For the detection of iron, I started with the precipitate from step 2h which was a light brown color. I then added 20 drops of 2 M sulfuric acid and boiled gently, which turned the solution a green color. Then, I added a drop of 6% H 2O2 and the precipitate dissolved. Then I added one drop of 0.2 M potassium thiocyanate turning the solution blood red instantly, proving the presence of iron.

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Fe3+ (aq) + KSCN (aq) → Fe(SCN)63- (aq) + K+(aq)

Co2+ -

Originally in the experiment, I detected no presence of the cobalt ion. However, the spot test proved the presence of cobalt. I added 15 drops of NH 4SCN in 50% alcohol to the solution. The solution turned purple showing both cobalt and iron were present. To further determine if cobalt was present, I added NaF(s) until the red color of iron disappeared leaving a teal blue solution proving the presence of the cobalt ion.

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Co2+(aq) + 4SCN-(aq) →Co(SCN)42- (aq)

Ni2+ -

With my unknown sample, I added 6 M NH 3 (aq) until the solution was alkaline. The solution then turned blue and no precipitate formed for me to decant. Then I added 4 drops of dimethylglyoxime. Upon addition, a strawberry red precipitate formed proving the presence of Ni2+.

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2(CH3)2C2N2O2H2 (aq) + Ni2+(aq) → H2O (l) + Ni[(CH3)2C2N2O2H]2 (s)

Cr3+ -

To the supernatant of step 3c of the experiment, I added 7 drops of 0.2 M barium chloride. No precipitate formed at this step, remaining a white cloudy mixture. Since no precipitate formed, I skipped to step 3g. I added 3 drops of 3 M nitric acid to the solution and heated it while stirring. No yellow or orange color formed in the solution. I then proceeded to add 10 drops of cold DI water then 10 drops of ether after letting it cool. I also added 1 drop of 6% H 2O2 . After mixing and allowing to settle, a blue color formed in the upper layer of the solution, proving the presence of chromium.

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Cr2O72- (aq) + 4H2O2 (aq) + 2H+(aq) → 2CrO(O2)2 + 5 H2O (l)...