Lab 7 report - The Separation and Identification of a Series of Cations

lab 7 report - The Separation and Identification of a Series of Cations
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Unformatted text preview: The Separation and Identification of a Series of Cations Yubo Liu Lab Partners: Leah, Dennis Due November 9 th , 2009 Yubo Liu Abstract The object of this experiment was to familiarize with cations’ reaction with 11 reagents. Some trends were found based on research and observations. The acid reagents didn’t generally form precipitates. The carbonate, phosphate, and chromate mostly formed precipitates and dissolved in nitric acid test. Hydroxides of some cations were amphoteric. Some metals formed amine complexes. Sulfides precipitated with most cations in basic solutions were black. Sulfides did not precipitate well in acidic conditions. Introduction The goal of this experiment was to identify cations, which were positively charged ions, in known samples based on their reaction in certain reagent solutions through performing qualitative analysis. Since substances and ions have their unique set chemical properties, qualitative analysis can be used to determine these properties from a known sample. Using these identified properties, chemists could run series of tests on unknown samples and figure out what the contents are in the unknown sample. In this experiment, the main concerns were to identify and familiarize with the cations’ properties. 10 cations were tested on their chemical reactions with acids, bases, and anions. Qualitative analysis can have all kinds of tests. Five different tests were performed in the experiment. They were standard anion test, ammonia test, basic sulfide test, acidic sulfide test, and confirmatory test. In addition, the nitric test would be performed on those with precipitates to test for solubility in acids. Each of the cations would react differently to the combination of all the tests and illustrated through visible evidences. Observations were made and recorded into a chart. They would be useful to identify cations from an unknown sample later on. During these tests in the experiments, the cations exhibited different behaviors. Understandings of these behaviors were crucial to identifying their chemical properties. The first was that the some cations’ hydroxides precipitates were amphoteric: A(OH) (s) + H + (aq) A + (aq) + H 2 O (l) (1) A(OH) (s) + OH- (aq) A(OH)- (aq) (2) The cations’ hydroxide could be both acids and bases. Since some metal hydroxides could dissolve in excess hydroxide and acids, this test was useful to isolate the amphoteric species from those that were not. The second were cations’ behaviors in aqueous ammonia. When ammonia reacted with water, only a small percentage reacted to form ammonia and hydroxide. Four possible outcomes were possible when some cations came in contact in the solution: a metal hydroxide precipitate could form, an amine complex (a metal with many anions bonded) could form, a metal hydroxide precipitate could first and then dissolve into an amine complex, or no reaction could happen. ...
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