CH 204 – Introduction to Chemical Practice Experiment #1 – (Qualitative Analysis of Cations) Valerie Tran* Kendrex White TA: Peiyu Tu June 08, 2016 RESULTS & DISCUSSION The purpose of this experiment was to identify the unknown cations in solutions in three different parts (A, B, C) using two types of qualitative analysis schemes. The first type of qualitative analysis scheme was utilized in Parts A & B. The qualitative scheme in Part A was primarily concerned with identifying lead or silver by analyzing the unknown metal nitrate solution. Part B’s focus was identifying barium or calcium in the unknown metal nitrate solution. The qualitative analysis scheme Part C utilized a different qualitative analysis scheme, the cation ion flame …show more content…
Through this experiment, the identities of the cations will be acquired and the types of qualitative schemes and proper use of lab equipment will become more familiar. The skill construction of a formula unit, total ionic, net ionic equations were acquired through the experiment. The results from Parts A & B were reasonable and expected. For Part A, the 6M HCl was added to the unknown metal nitrate (unknown number: 1) in Step 3 and immediately yielded solid white precipitate. The majority of the precipitate was at the bottom of the test tube, but there were bits of the precipitate in suspension. It looked similar to snow and was flaky. It was necessary to add HCl to the unknown because the cations must be completely precipitated in order for identification to be possible in this experiment. Cl- is soluble until it is combined to either lead, silver, or mercury. The addition of HCl can either yield lead chloride (PbCl2) which is slightly soluble or silver chloride (AgCl) which is insoluble . HCl also neutralizes any ions that contributed to the basicity of the solution, and in this case it was NO3- . In addition to neutralizing ions, HCl also affects Ba2+ or Ca2+to …show more content…
After (NH4)2CO3 was added to the basic solution, heat is applied to the test tube. It was then centrifuged and the liquid was discarded into a waste beaker. The precipitate was then washed with deionized water and centrifuged once again. Acetic acid was then added to the solid precipitate to dissolve it, resulting in a clear solution. Potassium chromate (K2CrO4) was added in step 12 because the chromate (CrO42-) ion and the unknown cation. This is vital in confirming the identity of the unknown cation in the metal nitrate solutions. Upon this addition of K2CrO4, the precipitate can turn yellow which presents the possibility of barium’s (Ba2+) presence. However, yellow precipitate was not a reliable confirmation of barium in solution. Assuming that barium ion was present could’ve led to a false positive. A false positive is when the test in an experiment resulted in an false, but seemingly correct