Identification of Anions and Cations in Solution
Purpose:
To identify the ions in an unknown solution through the application of chemical tests.
Background:
Detectives in mystery novels often rush evidence from the crime scene to the lab for analysis. In
this experiment, you will become a chemical detective. You will conduct laboratory analysis to
determine the composition of an unknown solution. The process of determining the composition
of a sample of matter by conducting chemical tests is called qualitative analysis. Solutions of
unknown ions can be compared to the results given by known ions, in the same tests. By
conducting the appropriate tests and applying logic, the identities of the ions present in an
unknown solution can be determined.
The analyses you perform are based upon the idea that no two ions produce the same set of
chemical reactions. Each ion reacts in its own characteristic way. In this experiment, you will
observe several types of chemical reactions commonly used as tests in qualitative analysis.
These reactions include a color change, the evolution of a gas, and the formation of a precipitatea solid product. As you do this experiment, remember that careful observation and logical
reasoning are the keys to being a good detective. Who knows what ions lurk in your unknown
solutions?
Equipment:
Safety goggles
4 Medium test tubes
Test tube rack
Bunsen burner
Dropper pipets
3 Q-tips
2 Pieces Red litmus paper
Test tube holder
Hot plate
400-mL Beaker
Wash bottle
Forceps
Distilled water
Chemicals:
Part A. Anions
0.1 M Silver nitrate, AgNO3
0.1 M Sodium sulfate, Na2SO4
0.1 M Barium chloride, BaCl2
0.1 M Sodium bicarbonate, NaHCO3
0.5 M Ammonium molybdate, (NH4)2MoO4
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0.1 M Sodium chloride, NaCl
1.0 M Sodium phosphate, Na3PO4
6 M Nitric acid, HNO3
6 M Hydrochloric acid, HCl
Part B. Cations
0.1 M Iron(III) nitrate, Fe(NO3)3
0.1 M Sodium chloride, NaCl
0.1 M Potassium thiocyanate, KSCN
0.1 M Calcium nitrate, Ca(NO3)2
1.0 M Ammonium chloride, NH4Cl
0.1 M Potassium chloride, KCl
6 M Sodium hydroxide, NaOH
0.1 M Ammonium oxalate, (NH4)2C2O4
Procedure:
As you perform the experiment, record your observation in the data tables. In testing for
different ions in steps 3-13 you will always begin with two test tubes. For each step you must
add 1 mL (~20 drops) of the known solution to one test tube, and 1 mL (~20 drops) of your
unknown solution to a second test tube. The name of the known solution is given in each step.
Always rinse the test tubes with water and clean them with soap and water after each step is
performed.
Part A. Testing for Anions
1. Set up a boiling water bath for use in steps 6 and 12.
2. Thoroughly clean all the test tubes used in this experiment, rinsing them well with distilled
water. Record the number of the unknown solution you will be testing.
3. Test for chloride ion, Cl . Known solution is sodium chloride. CAUTION: Nitric acid is
corrosive. Do not put your finger over the top of the test tube to cover it. Add 10 drops of 6 M
nitric acid to each tube containing the solutions to be tested and flick the tubes to mix. Add 10
drops of silver nitrate to each tube and flick to mix. Record observations. Dispose of the waste
in the silver waste container.
4. Test for sulfate ion, SO42 . Known solution is sodium sulfate. CAUTION: Hydrochloric acid
is corrosive. Add 10 drops of 6 M hydrochloric acid to each tube and mix. Add 10 drops of
barium chloride to each tube and mix. Record observations. Dispose of the waste in the barium
waste container.
5. Test for bicarbonate ion, HCO3 . Known solution is sodium bicarbonate. Carefully observe
the test tubes as you add 20 drops of 6 M hydrochloric acid to each tube. Record observations.
6. Test for phosphate ion, PO43 . Known solution is sodium phosphate. Add 10 drops of 6 M
nitric acid and 10 drops of ammonium molybdate solution to each tube and mix. Place the tubes
in a boiling water bath and heat for five minutes. Record observations.
7. Properly dispose of all solutions.
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Part B. Testing for Cations
8. Review the general directions at the beginning of the Procedure section. Prepare your test
tubes as you did for Part A, Step 2.
9. Test for iron(III) ion, Fe3+. Known solution is iron(III) nitrate. Add 5 drops of potassium
thiocyanate solution to each tube. Flick gently to mix. Record observations.
10. Flame test for sodium ion, Na+. Known solution is sodium chloride (use the vial of NaCl.)
Place a dry Q-tip into the sodium chloride solution. Place the Q-tip directly into a Bunsen burner
flame. Record the color immediately observed when the Q-tip is placed in the flame. Repeat the
procedure using a new Q-tip placed in the unknown solution.
11. Flame test for potassium ion, K+. Known solution is potassium chloride (use the vial of
KCl.) Repeat step 10 using potassium chloride solution. You do not need to test the unknown
solution again!
12. Test for calcium ion, Ca2+. Known solution is calcium nitrate. To each tube, add 10 drops
of ammonium oxalate. Warm the tubes in a boiling water bath for a few minutes. Record your
observations.
13. Test for ammonium ion, NH4+. Known solution is ammonium chloride. Caution: Sodium
hydroxide can cause burns. To each test tube add 3 drops of 6 M sodium hydroxide. Hold the
tube containing the ammonium chloride solution with a test tube holder. Gently warm the tube
along its sides using a back-and-forth motion through a “cool” burner flame. Do not allow the
solution to boil. Caution: At all times make sure that the opening of the tube is pointed away
from other people. Hold a moistened piece of red litmus paper near the mouth of the test tube
(be careful not to touch the sides of the test tube with the litmus paper. The test will be spoiled if
the solution contacts the litmus paper.) Record the changes you observe. Carefully fan the
vapors coming out of the tube towards your nose with your hand. Cautiously sniff the vapors.
Record your observations. Repeat the procedure for your unknown solution.
14. Dispose of all solutions as directed.
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