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+) Sodiumhydroxide (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 ofNaBiO3 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+.

Results

Cation / Reagent Added / Observation after first 1 drop/ / Observation after 20 drops / Solution added / Observations
After addition of H2O2 / Solution added / Observations
Mn2+ / NaOH / Light brown and cloudy / Same / H2O2 / Brown with precipitate / NH4OH/
Cr3+ / NaOH / Cloudy greenish blue / Clear green / H2O2 / Clear yellow / NH4OH
Ni2+ / NaOH / Light green Precipitate / same / H2O2 / same / NH4OH/ dimethylglyoxime
(DMG) / Strawberry-red precipitate
Co2+ / NaOH / Precipitate with blue / same / H2O2 / Dirty brown / NH4OH/ H2SO4 / Light Pink Color
Fe3+ / NaOH / Deep orange / Precipitate present / H2O2 / same / 1. NH4OH/ KSCN
2. NH4OH/ K4Fe(CN)6 / 1.Red color
2. Blue precipitate
Cu2+ / NaOH / Precipitate, light blue / Deep blue / H2O2 / Clear in the middle and blue at the top bottom / NH4OH/ Acetic acid
K4Fe(CN)6 / Blue color disappeared
Red precipitate
Zn2+ / NaOH / White Precipitate / Precipitate dissolved and clear / H2O2 / clear / NH4OH/ HCl / K4Fe(CN)6 / Zn3K2 [Fe(CN)6]2 Gray-blue precipitate

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
Zn2+ / Zn3K2 [Fe(CN)6]
Cu2+ / Cu2Fe(CN)6
Fe3+ / K4Fe(CN)6
Ni2+
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

Fe3+ +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% H2O2and 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+.

1