EXPERIMENT 5
Qualitative Analysis: Unknown Anions
First Practical Exam
Outcomes
After completing this experiment, the student should be able to:
1. Demonstrate their understanding of qualitative analysis.
2. Determine anion in an unknown using chemical methods.
3. Confirm their results with confirmatory qualitative tests.
Introduction
Students will use qualitative methods learned in previous experiment to determine anions in
two unknowns. Teaching Assistant/Instructor will provide two unknowns. Each will contain
one unknown anion.
Safety Precautions
Handle all the chemicals in this experiment with care. Avoid getting AgNO3 on skin or clothing; it
will stain dark-brown or black. Be especially careful when handling concentrated sulfuric acid,
H2SO4. It is one of the strongest and most corrosive concentrated acids. If any skin contact occurs,
wash with large amounts of water. If instructed to sample odors, do not inhale deeply, gently waft the
fumes toward your nose. Wear your safety glasses at all times which is required for all
experiments in which you use chemicals.
Materials and Equipment
Dropping bottles of 2 unknowns, conc. H2SO4, 6 M H2SO4, 6 M HNO3, 6 M HCl , 0.1 M Fe(NO3)3,
chlorine water,1 M BaCl2, 0.2 M FeSO4, AgNO3 solution, saturated KNO2, hexane, copper wool or
fine Cu wire, and 10 mL graduated cylinder.
Apparatus
Test tubes, test tube rack, test tube holder, stirring rods, pH paper, Bunsen burner, lead acetate paper,
centrifuge, 10-mL graduated cylinder, ring stand and clamp, boiling water bath, ice water bath and
spatula.
Hazardous Waste Disposal
All of the aqueous solutions may be washed down the drain with a large volume of water. The
hexanes or other organic solvents should be collected in a container for organic wastes.
Experimental Procedure
You may use flowchart on next page or procedure used in previous experiment to determine
anion in your unknown.
63
Flow sheet for the identification of unknown anions
CO32−
SO42−
PO43−
SCN–
Cl−
Br−
I−
NO3− CH3COO−
In test tube: 10 drops
unknown
add 6M H2SO4
dropwise
Gas evolution
(bubbles):
unknown is CO32−
No gas: negative test
Groups 2, 3 or 4
present
In new test tube, 10
drops unknown, add
10 drops BaCl2
White precipitate:
positive
PO43− or SO42−
Confirming test:
add 6 drops 6M HCl
Precipitate
dissolves:
PO43−
No precipitate:
negative
Groups 3 or 4
present
In new test tube: 10
drops unknown, add
10 drops AgNO3
Precipitate does
not dissolve:
SO42−
Positive: white or
yellow(ish)
precipitate
Negative (no ppt)
Unknown is NO3− or
CH3COO−
White ppt:
Unknown is SCN− or
Cl−
Yellow(ish) ppt:
Unknown is Br− or I−
Confirming test for
NO3− (brown ring)
New test tube: 10 drops
unknown+1 mL DW
add 2 drops Fe(NO3)3
Do confirmatory test
as given in previous
experiment for I− and
Br−
Confirming test for
Ac− (ester smell)
Dark red solution:
unknown is SCN−
Violet hexane layer:
I−
confirming test I−
No colour:
unknown is Cl−
confirming test for
Cl-
Brown hexane layer:
Br−
confirming test Br−
63
FIRST PRACTICAL EXAM
Identification of Unknown anions
Name:___________________________________________________
REPORT:
UNKNOWN 1
ID ___________________
Unknown Code: ____________
Write down your observations in the boxes given in the following table. You must submit this sheet to your instructor before leaving the lab.
CO32−
SO42−
PO43− SCN–
Cl−
Br−
I−
NO3−
CH3COO−
Group Test
Group
Test
Observation
Confirmatory Test (if any)
Conclusion
Test
Observation
Conclusion
Anion
Present
1
Acid-volatile
2
Barium
precipitate
3
Silver
precipitate
group
4
Soluble
group
Unknown anion is: _____________________________
63
FIRST PRACTICAL EXAM
Identification of Unknown anions
Name:___________________________________________________
REPORT:
UNKNOWN 2
ID ___________________
Unknown Code: ____________
Write down your observations in the boxes given in the following table. You must submit this sheet to your instructor before leaving the lab.
CO32−
SO42−
PO43− SCN–
Cl−
Br−
I−
NO3−
CH3COO−
Group Test
Confirmatory Test (if any)
Group
Test
Observation
Conclusion
Test
Observation
Conclusion
Anion
Present
1
Acid-volatile
2
Barium
precipitate
3
Silver
precipitate
group
4
Soluble
group
Unknown anion is: _____________________________
63