EXPERIMENT 29: ANION TESTS ADVANCE STUDY ASSIGNMENT Refer to the directions for

Question

EXPERIMENT 29: ANION TESTS ADVANCE STUDY ASSIGNMENT Refer to the directions for Experiment 29 when answering the following questions: 1. Each of the following tests was run on a different unknown solution. State which ion is indicated by the observation. Assume no interfering ions are present to complicate the test for each ion. a) Addition of 6 M NaOH and Al to the solution produces a gas which turns moistened red litmus paper blue. b) Addition of 6 M nitric acid makes a yellow solution turn orange. c) Addition of any strong acid produces an effervescence. d) Addition of silver nitrate produces a white precipitate. e) Addition of barium chloride produces a white precipitate. f) Addition of 6 M nitric acid plus 0.5 M ammonium molybdate produces a yellow precipitate 2. You are given an unknown which contains one or more of the 7 ions listed in this Experiment. You conduct the following tests, each on separate portions of the unknown. After each test, list the conclusion(s) drawn from that test. After the tests, tabulate the 7 possible ions as present, absent, or in doubt. a) Addition of 6M nitric acid causes no effect. b) Adding nitric acid and silver nitrate causes no effect. c) Adding nitric acid and 1 M barium chloride produces a white precipitate. d) Nitric acid plus ammonium molybdate produces a yellow precipitate. lons present lons absent lons in doubt

Explanation / Answer

1)

a) The anion present is nitrate ion (NO3-). Nitrate ions gets reduced to ammonia on reacting with NaOH and Al foil. This ammonia has pungent smell and changes red litmus blue because of basic nature.

b) Yellow solution is chromate ion (CrO42-). When it is reacted with nitric acid, it changes into dichromate ion (Cr2O42-), which is orange in colour.

c) The anion is carbonate ion (CO32-). This ion reacts with HCl to give CO2, which gives effervescence.

d) It is due to the presence of Cl- ion. It reacts with AgNO3 to form AgCl, which gives white precipitate.

e) Sulphate ion (SO42-) reacts with barium chloride to form barium sulfate which is insoluble white precipitate.

f) Presence of phosphate ions (PO43-) produces yellow precipitates on reacting with HNO3 and ammonium molybdate.

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