Understanding Of Basic Solubility Principles And Precipitation Reactions

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The purpose of this experiment was to apply the understanding of basic solubility principles and precipitation reactions to identify two unknown cations in a given solution. The first two processes involved adding various acids and basis to the unknown solution to observe different precipitation reactions. The unknown solution contained either silver or lead and either barium or calcium. For unknown solution one, adding a sample of hydrochloric acid to the unknown solution started the experiment. This was imperative because it triggered a precipitation reaction, creating PbCl2 or AgCl. HCl was an ideal acid that was used because it was soluble to Calcium or Barium but atleast partially insoluble to Ag and Pb, allowing for the Calcium or Barium to have remained in solution, become isolated in a new test tube, and set aside for later use.1 The chloride ions are much more attractive to the silver and lead ions compared to the calcium or barium, which allowed some to precipitate while others to have remained in solution.2

After the initial decanter, deionized water was added to the precipitate and the tube was placed in boiling water. This is an essential step, because this allows for the dissolution of any PbCl that might have precipitated. Since PbCl is slightly insoluble, if there was Pb in the unknown solution, the heating process would have caused it to become mostly soluble in the water. The addition of heat as a source of energy was enough to break the attractive forces

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