Finding The Presence Of Cations In An Unknown Solution Using Qualitative Analysis

The purpose of the experiment was to use two methods to find the presence of cations in an unknown solution using qualitative analysis. Qualitative analysis was used to identify a substance, not measure its amount. The first method used multiple solutions such as HCl, HNO3, H2SO4, NH4OH, acetic acid, K2CrO4, and K2C2O4 to conduct two tests. The first tested the presence of either Lead (Pb2+) or Silver (Ag+) while the second tested the presence of Calcium (Ca2+) or Barium (Ba2+). The second method used flames to burn metal ions in solution and observe the colors shown to identify the ion present in solution.

The purpose of Part A of the experiment was to test an unknown solution for the presence of either Pb2+ or Ag+. Unknown solution #3 was

This was done by first adding HCl to the solution. HCl was the acidic solution used as the reagent to make the precipitate. The attraction between the HCl and the unknown solution #3 was strong enough to create a solid. HCl acted as the anion and the unknown solution contained the cation. This formed an extra proton, or the hydrogen ion, and the precipitate. A centrifuge was used to separate the solid from the liquid solution. It worked by spinning the contents at a high speed, which creates a centrifugal force. 1 The denser solid moved towards the bottom of the test tube resulting in the separation. The centrifuge was balanced by placing another test tube, with the same volume, opposite to the test tube with the solution. The centrifuge needed to be balanced because if there were not equal volume in the test tubes, then there would be instability in the centrifuge causing it to be damaged. The liquid was decanted and set aside for later use. After the tube was centrifuged, HCl was added along with deionized water. It was then heated in boiling water. The tube was heated because it allowed the insoluble solid to be broken down since it was

The liquid that was set aside from Part A was used during this test. The solution turned out to be positive for calcium. This was done by first adding NH4OH to the solution. PH paper was used to verify that the solution was basic. The solution turned the paper blue verifying it was basic. (NH4)2CO3 was added to the solution. Then the tube was placed into warm water. Once the tube was cooled, the tube was centrifuged and 0.5 mL of 6M acetic acid was added to the precipitate. This was done to see if the precipitate turned cloudy. The solution was clear and not cloudy. The next instruction was to proceed to step 12 where two drops of 6M NH4OH and 0.5 mL of 1M K2CrO4 was added which caused the solution to turn orange. After the tube was centrifuged, a precipitate was not present. This step had chances of error due to a false positive. A false positive was described as a result that would indicate the presence of a substance that was not really in solution. Barium would be the cation that would be the false positive. The K2CrO4 was added because it acted as a reagent, which aided in identifying the presence of Barium or Calcium. K2CrO4 was the basic chemical that acted as the anion to find the unknown cation.2 The attractive forces between these substances was strong enough to form a precipitate. 0.5 mL of 6M HCl and 0.5 mL of 6M H2SO4 were added to see if the solution