Qualitative Analysis Lab

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Qualitative analysis, an analysis to determine the identity of a compound, was done on an unknown solution 4, passed by the Teaching Assistant at the beginning of the lab, to identify the cations contained. This unknown solution was known to contain two of four possible ions. The first section or Part A was to determine the existence of either lead ion or silver ion and the second section or Part B to determine the presence of barium ions or calcium ions. In addition, the cation flame test was used as another method of qualitative analysis of cations. HCl was added to the unknown solution 4 to separate out the cations in the first section and the second section. As expected, white precipitate formed. The test tube was centrifuged and the white…show more content…
Yellow precipitate formed after the addition of K2CrO4. The precipitate confirmed the presence of lead chromate, which has a vivid yellow color. Equation 1 showed the process and the result of the…show more content…
Barium chromate form yellow precipitate while calcium chromate stayed in aqueous form. After the addition, yellow precipitate formed which might indicate the presence of barium. The test tube was centrifuged and the resulting orange liquid was decanted into a new test tube. The formation of barium chromate may be a false positive. False positive imply the existence of a substance that is not present in a sample. In Part B, the formation of yellow precipitate could be a false positive for the presence of barium. HCl was added to the precipitate in order to dissolve barium chromate into barium chloride, an aqueous solution. H2SO4 was added next and white precipitate formed on the bottom of the test tube, confirming the existence of barium. Barium sulfate is a white precipitate. Equation 2 showed the process of the formation of barium sulfate and the result of the addition of H2SO4. The analysis for the presence of calcium was done to further refute the false positive of barium ions. NH4OH and K2C2O4 were added to the test tube that contained the orange liquid. White precipitate which would indicate the presence of calcium did not form. Calcium oxalate is a white solid. It was confirmed that unknown solution 4 contained lead ions and barium

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