Post-Lab Questions: 1. If you had a solution which contained only chloride, bromide, or iodide ion, which of the three tests would most clearly tell you which anion was in the solution? Explain. 2. Suppose that you were quite sure that your unknown contained only sulfate ion. Which test would most quickly (that is, in the fewest steps) confirm your hypothesis? Explain. 3. Consider each set of results below which were carried out on a solution containing either (1)one of the six anions studied in this experiment, or (2) none of these six ions (although other ions may be present). Give the formula of the ion present. (a) Silver Nitrate Test: A yellow precipitate forms. It dissolves when nitric acid is added. Barium Chloride Test: A white precipitate forms. It dissolves when hydrochloric acid is added. Chlorine Water Test: The hexane layer is nearly colorless after adding chlorine water. Anion: (b) Silver Nitrate Test: A yellow precipitate forms. It does not dissolve when nitric acid is added. Barium Chloride Test: A precipitate does not form. Chlorine Water Test: The hexane layer turns red-orange. Anion:
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If you had a solution containing only chloride, bromide, or iodide ions, the silver nitrate test would most clearly tell you which anion was in the solution. This is because each of these ions forms a different colored precipitate with silver nitrate: chloride Show more…
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A student performing this lab experiment receives his unknown solution, may contain ( SO4 2-, PO4 3-, Cl-, and NO3- ), and begins to conduct the following tests to identify the anions present 1) When the unknown solution was treated with Ba(NO3)2 and few drops of 5 M aqueous NH3, a white precipitate formed. 2) The white precipitate from 1 dissolves partially when few drops of 6 M HCl is added. Then no precipitate was formed when ammonium molybdate was added to the solution. 3) The resulting solution from step 1 was acidified with 6M HCl before the addition of aqueous silver nitrate which forms a white precipitate. 4) Another unknown solution was acidified with 6M H2SO4. No observation occurred after the addition of excess FeSO4 solution and conc. H2SO4. Which anions were present in the student's unknown solution? Select one or more: SO4 2- PO4 3- Cl- NO3-
Adi S.
3. For an unknown solution that contains at least one of the Group I cations, answer the following questions. (a) Upon adding 6 M HCl to the unknown solution, a white precipitate forms. What cation(s) may be present in the unknown? (b) When the white precipitate from (a) is treated with hot water, the white precipitate remains and a colorless supernatant is observed. The supernatant is pour into a new test tube. Adding K2Cr2O4(aq) to the colorless supernatant results in no reaction. What conclusion can be made about the presence or absence of Group I cations in the unknown? (c) When the precipitate from (b) is treated with 6 M NH3(aq), it dissolves. If HNO3 were then added to the resulting solution, what would you expect to observe? Give the balanced net ionic equation, including phase symbols, for the reaction that occurs upon addition of the HNO3. 4. A solution may contain Ag+, Pb2+, and/or Hg22+. A white precipitate forms when 6 M HCl is added. The precipitate is partially soluble in hot water. The supernatant and the precipitate are places into two separate test tubes. The solid remaining after treatment with hot water turns black on addition of 6 M NH3. The supernatant is tested with K2CrO4 and a yellow precipitate forms. No other precipitates are observed while preforming the procedure. Which of the ions are present and which are absent? State your reasoning.
Which ion is present in each of the following samples? The sample gives white precipitate when treated with AgNO3 (silver nitrate). Cl- The sample gives white precipitate when treated with Na2CO3 (sodium carbonate). Cu+2 The sample gives off bubbles when treated with acid. CO2 Which ion or ions are shown to be absent from the following samples? The solution does not turn red when treated with KSCN (potassium thiocyanate). Fe+3 The solution does not turn dark blue when treated with ammonia (NH3) solution. Cu2+ If an unknown sample yielded the following results, then what is the formula for the unknown compound? Observation Ion Tested Result (+ or -) Reagent Added HNO3 No bubbles CO2 CO2 Remains clear Ca2+ AgNO3 White precipitate C Blood red Fe+3 KSCN Remains clear Cu2+ NH3 or NH4OH Cu2+ Symbol for anion present CO3^2- Symbol for cation present CuCO3 Formula for compound CuCO3 Sample of tap water with some silver nitrate (AgNO3)? What do you think would happen if you treated it with chloride form & cloudy solution? It would form silver chloride.
Sri K.
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