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Qualitative Anion Tests Essay

Procedure

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(PO43-): 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 (SO4 2-): 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 sulfate.

● Sulfide (S2-):Acidify 10 drops of the test solution with HCl. The odor of hydrogen sulfide (H2S) should be apparent (it smells like rotten eggs!). Warm the solution moderately and then hold a small piece of moist lead acetate paper at the mouth of the test tube. If the paper turns black (caused by PbS) this indicates the presence of sulfide. Thoroughly clean and dry the test tubes before beginning tests on the next solution. Cleanup: Tightly cap the bottle of silver nitrate solution and put it in the Experiment 11 bag so it will be easy to find when you need it for the next experiment. Flush any other remaining solutions down the drain with lots of water. Properly rinse all equipment used, then dry and store for future use.

Data and Observation

Data Table: Qualitative Anion Tests Name
Test tube 1
w/HCI
Test tube 2
w/AgNO3
w/HNO3
Test tube 3
Confirmation
Bromide
Gas and no smell
Precipitate, didn’t dissolve
Didn’t dissolve
Iodine separated from Bromide
Carbonate
Gas and no smell
Cloudy Precipitate
Clear gas present
Clear and no smell
Chloride
Gas and no smell,
No precipitate

Cloudy precipitate present
Didn’t dissolve
Dissolve with precipitate present
Iodine
Gas and no smell
Precipitate, didn’t dissolve
Didn’t dissolve
Iodine separated from Bromide
Phosphate
Gas and no smell
Cloudy and yellow precipitate present
Dissolve
Yellow with precipitate present
Sulfate
Gas and no smell
Precipitate present
Didn’t dissolve
White precipitate present
Sulfide
Gas and clear
Precipitate present
Didn’t dissolve
Had an odor with precipitate present.
Turned Black
Unknown
No change
No change
White precipitate present
Sulfate didn’t dissolve

Questions:
Group 1: Anions that WILL NOTPRECIPITATE in the presence of silver nitrate.

Sulfate

Group 2: Anions that WILL PRECIPITATE in the presence of silver nitrate and the resulting precipitates WILL DISSOLVE upon acidification with nitric acid.

Carbonate, Phosphate

Group 3: Anions that WILL PRECIPITATE in the presence of silver nitrate and the resulting precipitates WILL NOT DISSOLVE upon acidification with nitric acid.

Bromide, Chloride, Iodide, Sulfide

A. Write a net ionic equation for any reaction that produces a precipitate.

Sodium Bromide:
Ag+(aq) + Br-(aq) ( AgBr(s)
Sodium Carbonate:
2Ag+(aq) + CO32-(aq) ( Ag2CO3(s)
Sodium Chloride:
Ag+(aq) + Cl-(aq) ( AgCl(s)
Sodium Iodide:
Ag+(aq) + I-(aq) ( AgI(s)
Sodium Phosphate:
Ag+(aq) + PO4-(aq) ( Ag3PO4(s)
Sodium Sulfide:
2Ag+(aq) & S-2(aq) ( Ag2S(s)

B. Identify the anions that produce gas upon addition of HCl.

Carbonate, Sulfide

C. Identify the anions that do not precipitate with silver nitrate.

Sulfate

D. Identify the anions that react with silver nitrate to form precipitates that dissolve when acidified with nitric acid.

Carbonate, Phosphate
E. Identify the anions that react with silver nitrate to form precipitates that do not dissolve when acidified with nitric acid.

Bromide, Chloride, Iodide, Sulfide

F. What simple test (other than a specific confirmation test) would distinguish between CO3 2-and NO- ?

Add Barium Chloride. If there is CO32- a white precipitate of BaCO3 will appear.

Conclusions:

Through this experiment, I learned how to identify commonly occurring anions. I also learned how to use the characteristics of their reactions with HCl and AgNO3 to identify an unknown solution. Using my observations with the different anion mixtures, I was able to identify the Unknown anion to be Sodium Sulfate. I figured this out because when HCl was added, no gas was formed. This ruled out Sodium Carbonate and Sodium Sulfide. The gas I observed for the Sodium Carbonate & Sulfide was very subtle. Even then I was not 100% sure. This is where I think there could have been room for error because I did not read the results correctly, therefore possibly interfering with my unknown. However, the unknown did not form a precipitate and there was only one other anion that did this.


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