Experiment 19
Qualitative Cation Analysis

1. A Groups III, IV, and V unknown is a pale yellow solution.

2. One drop of the unknown is added to 50% NaOH in a casserole dish. The moist red litmus suspended above the casserole turns blue immediately. (The mixture in the casserole looked like red mud.)

3. When a sample of the unknown is made basic with a NH₃/NH₄Cl buffer, a brown precipitate forms leaving a colorless decantate.

4. The precipitate from 3 is dissolved in HCl and HNO3. Addition of NaOH and H₂O₂ and heating results in the formation of a brown precipitate and colorless decantate.

5. The decantate from 4 gives a white precipitate when acidified with acetic acid and treated with lead(II) acetate.

6. When ammonium carbonate is added to the decantate from 3, a white precipitate forms. The decantate is colorless. Dissolving of the precipitate in acetic acid followed by addition of potassium chromate gives a yellow precipitate.

7. Addition of ammonium oxalate to the yellow decantate from 6 gives no precipitate.

8. Cation(s) present in the unknown: