Common Anions and Cations Lab

Period 3

The purpose of this lab was to identify common anions and cations in solutions using simple chemical tests, and to use the results discovered in these tests to identify ions in an unknown solution.

First we tested for anions, skipping the boiling bath described by step one; we tested for the chloride ion. To do so we added 2 mL of sodium chloride to a clean prepared test tube. To a second clean test tube we added 2 mL of the unknown substance-A102. One mL equaled about 20 drops per test tube. We then proceeded by adding 2mL of 6M nitric acid to each test tube, and flicked gently to mix them up. Both test tubes came up with a white, chunky, chalky mixture. We decided prematurely that the chloride ion was present in solution A102.

Our next test for was sulfate ions. We prepared a test tube, which had been cleaned, with 2 mL of sodium sulfate solution, and another tube with 2mL of unknown. 2mL of 6M hydrochloric acid was added to each. The sodium sulfate solution became white, and thinned. However, the unknown had very little affected-if any-and was clear.

Our next test was for bicarbonate ions. We added 2mL of sodium bicarbonate and the unknown solution to two separate test tubes. We watched very carefully, as directed, as we added the 6M hydrochloric acid. The sodium bicarbonate solution stayed clear, but became very bubbly. The unknown-A102-stayed unaffected in this test.

We then tested for phosphate ions. Once again we added 2mL of sodium phosphate and the unknown to two separate test tubes. We proceeded to add 1 mL (10 drops) of 6M nitric acid and 10 drops of ammonium molybdate to each test tube. They were placed in the boiling bath we had now prepared (day 2). The test may have been obscured, but no results came from either test.

In our next set of steps, starting at 7, we were now testing for cations. Our first test was for iron (III) ions, and to do so we added 2mL of sulfate solution, and 2mL of the unknown to two tubes. We also added 5 drops of both sulfuric acid and potassium thiocyanate to each tube. We then flame tested both tubes, and this resulted in our unknown remaining unchanged and the Iron (III) turning red.

Then we tested for potassium ions. 2mL of both the potassium chloride in one tube, and the unknown in another, were added. 3 drops of 6M hydrochloric acid were added. These solutions were flame tested with a clean wire-resulting in a purple color for the potassium chloride, and nothing for the unknown.

We finally tested for ammonium ions using some litmus paper. We added 2mL of ammonium nitrate solution to one test tube, and the unknown to another. 3 drops of 6M of sodium hydroxide were added to both tubes. Each tube was warmed separately, and the litmus paper was held closely at the top. The ammonium nitrate solution turned the litmus paper blue. The unknown had no affect.

The result from our experiments showed that the anion present in solution A-102 was in fact chloride. We, however, didn’t find our cation due to some faulty labs results incurred by more than one lab group.