Five Unknown Analysis Procedure
1. Test all 5 tubes with pH paper.
2. Separate the acid tubes from the basic tubes
3. To the basic tubes a copper nitrate test should be run. A pale blue solution means that
NaOH is present; if the solution turns a deep blue, then NH3; or if a black precipitate
forms then Na2S is present. With the other tubes, perform all the tests that will be
performed on the acidic tubes.
4. To the acidic tubes, test each of the tubes with a sulfate test. If a white precipitate
forms, then sulfate is present. Which means either Na2SO4 or H2SO4 is one of the
unknown.
5. To any of the acidic tubes that didn’t have sulfate, then a chloride test needs to be
performed. A white precipitate proves that chloride is present. If present, then HCl,
NaCl, BaCl2, or CuCl2 is the unknown.
6. To any of the acidic tubes that didn’t contain sulfate or chloride, then an iodine test
needs to be performed. If the hexane layer doesn’t turn violet, then no iodine is present.
If present, NaI is the unknown present.
7. If no iodine, chloride, or sulfate is present, then a nitrate test needs to be performed. A
lack of a brown ring indicates nitrate is not present. If nitrate is present, then AgNO3,
Cu(NO3)2, or Fe(NO3)3 could be one of the unknowns.
8. For the tube that contained the chloride, a barium test should be run. If a white
precipitate forms then the tube contains BaCl2.
9. If the chloride tube did not have barium, then a copper test should be run. If the solution
turns a dark blue then copper is present and the unknown is CuCl2. If neither barium
nor copper are present, then a look at the pH will tell if the solution is HCl or NaCl. A
very low pH indicates the presence of HCl.
10. To the tube that contained the nitrate, a silver test should be performed. If a white
precipitate forms that confirms the presence of AgNO3.
11. If no silver is present, then a copper test should be performed. If the solution turns a
dark blue color, then copper is present and the unknown is Cu(NO3)2.
