Flame Test Lab Report Essay

In this experiment, two qualitative analysis techniques were used to determine the identities of two unknown cations in a solution. The first technique relied on the solubility, and lack thereof, of various salts, and the second relied on the characteristic flame colors that various cations produced. First, the presence of either lead or silver was confirmed by testing a precipitate obtained through centrifugation of the unknown solution. Then, the presence of either barium or calcium was confirmed in the liquid decanted during the previous test. These first two tests were composed of various reactions that created an insoluble salt of the cation being tested, which settled down as a precipitate. Finally, cation flame tests were performed on

A centrifuge operates by rapidly spinning its contents, creating a centrifugal force that causes the denser components of a mixture, in this case various precipitates, to settle at the bottom.1 The centrifuge was balanced by placing test tubes of equal size, containing equal volumes of solution in various configurations in order to spread out the weight of the samples equally in the centrifuge. In the case of the six slot centrifuge used in the experiment, if two or four test tubes were present, they were placed in slots opposite to each other, either individually, or in pairs depending on whether there were two or four test tubes respectively. If three test tubes were present, they were placed with a slot left empty between them, in the form of an equilateral triangle. If six test tubes were present, all slots were filled. If one or five test tubes were present, a blank test tube filled with water to a volume equivalent to the solution being centrifuged was used to balance the centrifuge. Had these precautions not been taken, the centrifuge could have been permanently damaged due to an unequal amount of centrifugal force applied in different

K2CrO4 was added to the solution in order to create a solution with Ca2+ cations because CaCrO4 is completely soluble, and was dissolved in the solution, while BaCrO4 is insoluble. The resulting orange solution with possible Ca2+ ions was decanted. A yellow precipitate was observed, which could have indicated the presence of barium in the form of barium chromate, a yellow salt. However, this was proven to be a false positive, a test which incorrectly confirms the presence of a substance, when the presence of calcium ions was confirmed by the precipitation of CaC2O4, a white precipitate, in step 14. In this case, the presence of barium was incorrectly confirmed by the false positive. The observed yellow precipitate was formed due to the reaction of leftover lead ions from part A with potassium chromate, to produce lead chromate, which is also a yellow precipitate. While this observation was unusual, it was expected, especially since lead had been confirmed in part A, making the occurrence of the false positive more likely. The various chemical equations for part B were as