Reactivity of Halide Ions
Observe the reactions of the halide ions with different reagents
Analyze data to determine characteristic reactions of each halide ion
Infer the identity of unknown solutions
Introductions: The four halide salts used in this experiment are found in your body. Although sodium
fluoride is poisonous, trace amounts seem to be beneficial to humans in the prevention of tooth decay.
Sodium chloride is added to most of our food to increase flavor while masking sourness and bitterness.
Sodium chloride is essential for many life processes, but excessive intake appears to be linked to high blood
pressure. Sodium bromide is distributed throughout body tissues, and in the past it has been used as a
sedative. Sodium iodide is necessary for the proper operation of the thyroid gland, which controls cell
growth. The concentration of sodium iodide is almost 20 times greater in the thyroid than in blood. The need
for this halide salt is the reason that about 10 ppm of NaI is added to packages of table salt labeled “iodized.”
The principal oxidation state of the halogens is –1. However, all halogens except fluorine may exist in other
oxidation states. The specific tests you will develop in this experiment involve the production of recognizable
precipitates and complex ions. You will use your observations to determine the halide ion present in an
unknown solution.
Objectives
Safety: For this experiment, wear safety goggles, gloves, and a lab apron to protect your eyes, hands,
and clothing. If you get a chemical in your eyes, immediately flush the chemical out at the eyewash station
while calling to your teacher. Know the location of the emergency lab shower and eyewash station and the
procedure for using them. Do not touch or taste any chemicals. If you get a chemical on your skin or
clothing, wash the chemical off at the sink while calling to your teacher. Follow all instructions, do not mix
chemicals randomly. Call your teacher in the event of a spill. Spills should be cleaned up promptly,
according to your teacher’s directions. Never put broken glass into a regular waste container. Broken glass
should be disposed of properly in the broken-glass waste container.
Materials
Procedure
0.1 M AgNO3
3% starch solution
0.1 M NaCl
4 M NH3 (aq)
0.2 M KBr
5% NaOCl (commercial bleach)
0.2 M Kl
24-well micro plate
0.2 M Na2S2O3
Toothpicks to stir reaction.
1. Put 5 drops of 0.1 M NaCl into the first four wells in row 1, as shown in the Figure below.
Put 5 drops of 0.1 M KBr into the first four wells in row 2. Put 5 drops of 0.2 M KI into the
first four wells in row 3 and Leave Row 4 empty. Reserve rows 5 and 6 for unknown solutions.
2. Add 2 drops of 0.1 M AgNO3 solution to each of the halides in columns A, B, and C. Record
in your data table (first column) the colors of the precipitates formed.
3. Add 5+ drops of 4 M NH3 (aq) to the precipitates in column B. PLEASE BE CAREFUL,
DO NOT ADD NH3 TO BLEACH. Stir carefully and record your observations in the data
table (second column).
Column A
a. AgNO3
Column B
a. AgNO3
b. NH3
Column C Column D
a. AgNO3
Starch +Bleach
b. Na2S2O3
1. NaCl
1. NaCl
2. KBr
2. KBr
3. KI
3. KI
4. EMPTY
4. EMPTY
5. Unk #1
5. Unk #1
6. Unk #2
6. Unk #2
4. Add 5+ drops of 0.2 M Na2S2O3 solutions to the precipitates in column C. Record your
observations in the data table.
5. To the halides in column D, add 5 drops of starch solution and 1 drop of 5% bleach solution.
Record your observations. Save the results of testing the four known solutions for comparison
with the tests of the unknown solutions.
6. Obtain the single unknown solution. Put 5 drops of the unknown in each of the four wells in
row 5. Add the reagents to each well as you did in steps 2-5. Compare the results with those
of the known halides in row 1-3. Record your finding in the data table, and identify the
unknown.
7. Obtain the double unknown solution containing a mixture of two halide ions. Place 5 drops
of the unknown mixture in each of the four wells in row 6. Add the reagents to each well as
you did in steps 2-5. Record your results. Compare the results with known halides in rows 13. Identify the unknowns.
Cleanup and Disposal
Rinse the microplate as instructed by your teacher. Wash your hands thoroughly before you leave the
lab and after all work is finished.
DATA TABLE
Halide
Salt
AgNO3
AgNO3 +
NH3
AgNO3 +
Na2S2O3
NaOCl +
Starch
NaCl
KBr
KI
Single
Unknown
Double
Unknown
Calculations
1) Indicate the single unknown number.
2) Determine the identity of the single unknown.
3) Include a few statements justifying your decision in # 2 above.
4) Indicate the double unknown number.
5) Determine the identity of the double unknown.
6) Include a few statements justifying your decision in #5 above.
Questions
1) Which procedure(s)confirm(s) the presence of (a) Cl- ions, (b) Br- ions, and (c) I- ions.
a _______________________________________________________________________
b _______________________________________________________________________
c _______________________________________________________________________