Exercise 14: Qualitative Anion Tests
The purpose of this experiment is to identify some commonly occurring anions & to study some of the reactions used for their identification.
You must first determine to which of the three groups the various anions belong. Since no two people observe the same event in exactly the same way it is important to also conduct specific confirmation tests on the known samples of each anion. This information will help identify the anion present in the unknown solution. After determining to which group the unknown solution belongs the specific confirmation test will enable you to conclusively identify which anion is present in the unknown solution.
1. Before beginning, set up a data table similar to the Data Table: Qualitative Anion Tests in the Lab Report Assistant section.
2. Each anion tested will require the use of three separate test tubes. Complete all of the following tests on one solution, record your observations, and then thoroughly clean and dry the test tubes before beginning tests on the next solution.
3. After consecutively testing the identified anions, perform the same tests on the unknown solution to conclusively determine its identity.
4. First test tube:
a. Put 8 drops of the anion to be tested in a clean small test tube.
b. Add 8 drops of hydrochloric acid to the anion solution. Note the appearance of the
solution plus any evolution of gas and odors of gas.
5. Second test tube:
a. Put 8 drops of the anion solution in a second test tube.
b. Add 3 drops of silver nitrate solution.
c. Note the colors of any precipitates formed.
d. Write a net ionic equation for any reaction that produces a precipitate.
e. Acidify the test tube by adding a few drops of nitric acid.
f. Mix well and note if the precipitate dissolves or remains.
6. Third test tube: Per the following, perform the appropriate confirmation test for this anion. NOTE: Where the following instructions call for “gently warming” a chemical place the test tube containing the chemical into a 50-mL beaker of hot tap water for a few minutes.
-- Bromide (Br-) and Iodide (I-): (First make fresh chlorine water by combining in a
graduated cylinder approximately 1ml of bleach, 5ml of tap water, and 6 drops of HCl;
stir or shake. Then label an empty pipet and suck up this chlorine solution for use here.)
To 10 drops of the test solution add 2 to 3 drops of the organic reagent (hexanes or
similar) and several drops of chlorine water. Shake well and allow the lower layer to
settle out. Note the color in the organic reagent layer. A brown or gold color indicates
bromine and a reddish-violet or pink color indicates iodine.
-- Carbonate (CO32-): Acidify 20 drops of the solution with 2 drops of HCl. Carbonates
produce an odorless gas (CO2) which should produce a precipitate when bubbled through
a saturated calcium hydroxide solution. For the purpose of this experiment you may
distinguish this gas from hydrogen sulfide by its lack of odor (See sulfide test, S2-).
-- Chloride (Cl-): To 6 drops of the test solution add 2 drops of AgN03, silver nitrate
solution. A white precipitate that dissolves readily when the solution is made definitely
basic with aqueous ammonium indicates the presence of the chloride ion.
-- Phosphate (PO4 3-): Acidify 10 drops of the test solution with 1 drop of HNO3, nitric
acid, and add 7 drops of ammonium molybdate solution (shake it well before using). Wait
30 seconds. The phosphate should produce a yellow precipitate. Gentle warming may be
necessary to obtain the precipitate.
-- Sulfate (SO42-): To 10 drops of the test solution add 5 drops of the BaCl2, barium
chloride solution. A white precipitate that is insoluble in HCl indicates the presence of
-- Sulfide (S2-): Acidify 10 drops of the test solution with HCl. The odor of hydrogen
sulfide (H2S) should be apparent (it smells like rotten...
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