LAB – QUALITATIVE ANALYSIS OF ANIONS
Name___________________
Chemicals:
Solutions of anions:
0.2 M solutions of sodium chloride (NaCl), potassium iodide (KI), sodium bromide (NaBr),
sodium sulfate (Na2SO4), sodium nitrate (NaNO3), sodium carbonate (Na2CO3)
Test reagents:
Silver nitrate, AgNO3, 0.1 M
Potassium permanganate, KMnO4, 0.1 M
Nitric acid, HNO3, 6 M
Acetic acid, HC2H302, 6 M
Ammonia, NH3, 6 M
Sodium hydroxide, NaOH, 6 M
Mineral oil
Barium Chloride, BaCl2, 0.1 M
Barium Hydroxide, Ba(OH)2, saturated
Aluminum granules
Iron(III) nitrate, Fe(NO3)3, 0.1M in nitric acid (0.6M)
To neutralize spills:
Baking soda, NaHCO3(s)
Equipment
Test tubes, 6, 13- x 100-mm
Beaker, 250-mL for hot water bath
Beral pipets, graduated
Centrifuge
Vinegar, HC2H3O2
Test tube rack
ceramic hot plate
pH paper
Procedure
Safety Alert
Most of the acids and bases used are very concentrated and can cause chemical bums if spilled.
Handle them with care. If you get acid or base on yourself, wash it off with lots of water. Small
spills (a few drops) can be cleaned up with paper towels. Larger acid spills can be neutralized with
baking soda, NaHCO3, and then safely cleaned up. Neutralize base spills with a vinegar solution
(dilute acetic acid). Some of the solutions are poisonous. Wash your hands when you are finished.
Solutions containing silver ions and potassium permanganate cause stains which do not appear for several
hours. If you think you spilled any of the solution containing silver ions on yourself, wash off with soap
and water. Wear Chemical Splash Goggles and a Chemical-Resistant Apron.
Proper Use of Centrifuge.
Before turning the centrifuge on, make sure the test tubes in the device are as evenly-distributed as
possible. If you have only one test tube to spin, balance it with a test tube filled with water.
Preparation of a Solution for Analysis.
Prepare a known solution by combining 1 mL of each ion to be tested. The total solution volume
will be about 6 mL.
To analyze an unknown solution, use about 1.5 mL of the solution that your teacher will give you.
1. Separation of the Halides(Cl-, Br-, and I- ) and confirmation of Chloride.
Place 10 drops of the test solution (or unknown) into a test tube. Test to see if the solution is acidic. If it is
not, add 6M acetic acid dropwise with stirring until the solution is acidic. Add 10 drops of 0.1M silver
nitrate. A precipitate of AgCl, AgBr, and AgI will form. Centrifuge and dispose of the supernatant liquid.
Wash the precipitate with ½ mL of distilled water, centrifuge, and discard the wash water.
Add 0.5 mL of 6M ammonia to the precipitate. Stir to dissolve any AgCl. Centrifuge and pour the
supernatant liquid into another test tube to confirm the chloride ion. Discard the remaining precipitate in
the appropriate container.
Add 1mL of 6M nitric acid to the solution containing the chloride ion. The solution will get hot and smoke
from the reaction with the excess ammonia whether or not there is any chloride present. Test to see if the
solution is acidic. If not, add nitric acid until the solution is acidic. The appearance of a white precipitate
(AgCl) confirms the presence of chloride.
LAB – QUALITATIVE ANALYSIS OF ANIONS
Name___________________
2. Separation and Confirmation of Bromide and Iodide.
Place 10 drops of the original test solution (or unknown) into a test tube. Add 6M nitric acid dropwise with
stirring until the solution is acidic. Add 1 mL 0.1 M iron(III) nitrate/nitric acid solution and stir. Then add
1 mL of mineral oil, stopper the test tube with a cork stopper and shake for 30 seconds. The presence of a
pale pink to purple color in the mineral oil layer (top layer) due to dissolved iodine confirms the presence
of iodide in the solution.
Draw the mineral oil layer off the solution with a pipet and discard in the organic waste container. Add
0.1M potassium permanganate solution dropwise with stirring until the solution remains pink. Again add 1
mL of mineral oil, cork, and shake the test tube for 30 seconds. The presence of a yellow to brown color in
the oil layer due to dissolved bromine confirms the presence of bromide in the solution.
3. Confirmation of Carbonate.
If any bubbles were formed when acid was added to the original solution, carbonate is probably present and
CO2 is being formed. A confirmation of the presence of carbonate involves reacting evolving CO 2 with
barium hydroxide to form barium carbonate, an insoluble, white precipitate.
Place 2 mL of clear, saturated barium hydroxide solution in a test tube to be available for the test with CO 2.
Place 1 mL of the original test solution (or unknown) in a different test tube. Acidify this solution by
adding 0.5 mL of 6 M nitric acid. Take a wide-stem pipet and cut off the tip so that the opening is the same
size as the barrel of the pipet. Place the tube in a hot water bath and observe to see if any gas bubbles form.
Take the pipet and squeeze the bulb closed. Place the tip of the pipet close to, but not touching, the surface
of the liquid in the test tube and slowly release the bulb to draw escaping CO 2 into the pipet. Put the pipet
into the barium hydroxide solution. This procedure may be repeated if necessary. The formation of a
cloudy, white precipitate (BaCO3) confirms the presence of the carbonate ion.
4. Confirmation of Sulfate.
Place 0.5 mL of the original test solution (or unknown) in a test tube. Add 6M nitric acid dropwise until
the solution is acidic. Then add 0.5 mL of 0.1 M barium chloride solution. The formation of a white
precipitate (BaSO4) confirms the presence of sulfate.
5. Confirmation of Nitrate.
Place 1 mL of the original test solution (or unknown) in a test tube. Add 6M NaOH dropwise until the
solution is basic, and then add another 6 drops of NaOH. Use a pipet to transfer the solution to the bottom
of a dry, LARGE test tube without getting the walls of the test tube wet with solution. Obtain some
aluminum granules on the tip of a microspatula and add them to the solution in the test tube. Place a small
cotton wad loosely about halfway down the test tube, but not touching the solution. This is to prevent
spattering of the solution onto the pH test strip. Hang a piece of moist pH paper in the tube so the bottom
of the paper is close to (but not touching) the cotton. Now warm the solution in a hot water bath until it
starts to bubble strongly. Be sure that the solution and the cotton do not touch the litmus paper, or the
litmus paper will turn blue, giving a false positive test. If the moist paper turns blue, starting at the bottom
and spreading to the top, this indicates the evolution of ammonia and confirms the presence of nitrate in the
original solution.
Discussion
Your laboratory report should contain all of your data from the analysis of the known solution as well as
your unknown solution. State clearly which ions were shown to be present and which ions were proven
absent. ,
In your report also include answers to the following questions:
1. The confirmatory test for the chloride ion with silver is the same chemical reaction used to confirm silver
in the cation analysis scheme. Explain what the reaction is and how the initial precipitate is dissolved and
reprecipitated. Use equations in your answer.
2. The procedure for chloride analysis makes use of the fact that AgCl can be dissolved in ammonia, but
neither AgBr nor AgI will dissolve in ammonia. Look up the solubility products (K sp) of AgCl, AgBr, and
AgI and show how their relative solubilities agree with this fact.
LAB – QUALITATIVE ANALYSIS OF ANIONS
Name___________________
Qualitative Analysis of Anions
Flow Chart
Cl- Br- I- SO4-2 CO3-2 NO3-
AgNO3
1
SO4-2 CO3-2 NO3-
AgCl(s) AgBr(s) AgI(s)
1
NH3
Ag(NH3)2+
AgBr(s) AgI(s)
HNO3
Cl-
1
AgCl(s)
Cl- Br- I- SO4-2 CO3-2 NO3-
Fe(NO3)3
2
Cl- Br- SO4-2 CO3-2 NO3-
I2(s)
2
Br2(s)
Fe(NO3)3
Cl- SO4-2 CO3-2 NO3-
LAB – QUALITATIVE ANALYSIS OF ANIONS
Name___________________
Qualitative Analysis of Anions
Flow Chart (con’t)
Cl- Br- I- SO4-2 CO3-2 NO3-
HNO3
3
Cl- Br- I- SO4-2 NO3-
CO2(g)
Ba(OH)2
Cl- Br- I- SO4-2 CO3-2 NO3BaCO3(s)
4
BaSO4(s)
Cl- Br- I- SO4-2 CO3-2 NO3-
5
NH3(g)
NaOH
Al
Cl- Br- I- SO4-2 CO3-2
BaCl2
Cl- Br- I- CO3-2 NO3-