MCHS Chemistry
Laboratory Notes
Ms. Robinson Date:_______ Class: ____ Name:____________________
Lab: Periodic trends of halogens
Objectives: explore similarities and differences in chemical
properties and reactivity of halogens and their halide ions.
Halogen element loses an electron Æ Halide ion – (stable full octet)
Safety:
Bromine water and chlorine water are toxic by ingestion and inhalation. Do
not breathe bromine and chlorine vapors. Bromine and iodine water are skin
and eye irritants. Avoid contact of all chemicals with eyes and skin. Hexane
is a flammable organic liquid. Do not allow hexane to come into contact with
heat, flames or other sources of ignition. Wear chemical splash goggles and
chemical-resistant gloves and apron.
Write your lab responsibility here: ____________________________
(safety officer, equipment manager, data collector, research organizer).
Pre-lab questions:
1. Read the entire lab handout and recommended safety precautions.
What hazards are associated with the use of halogens in the lab? How
can these hazards be avoided?
2. Chlorine (Cl2) is used in water treatment plants and in swimming pools.
Why is chlorine added to drinking water and swimming pool water?
(You may want to do the lab before answering this question)
Follow safety procedures!
MCHS Chemistry
Laboratory Notes
Ms. Robinson Date:_______ Class: ____ Name:____________________
3. The following table shows the boiling points of the halogens. Boiling
points depend on the bonding between molecules or ions, with high
bonding forces producing higher boiling points than weak forces.
Describe in words the periodic trend that is observed in the table
below. How can you explain the trend in relation to bonding and the
trend in number of electrons of each element?
Halogen
Boiling point
F2
-188 oC
Cl2
-34oC
Br2
58oC
I2
184oC
Lab activity:
Part A Color and appearance of the halogens
Hexane is an organic solvent that does not dissolve in water. Chlorine,
bromine and iodine will be identified by their color and appearance in both
water and hexane. The halogen elements (uncharged) dissolve better in the
non-polar (uncharged) hexane. The halogen ions (charged) dissolve better in
polar (charged) water.
1. Place six clean test tubes in a test tube rack. Label the tubes 1-6
using tape and a sharpie marker.
2. Use a pipet to add 10 drops of chorine water (Cl2 ) to tubes 1 and 2.
3. Use a different pipet to add 10 drops of bromine water (Br2) to tubes
3 and 4. Place the pipets you are using on a clean paper towel.
4. Use a third pipet to add 10 drops of iodine solution (I2) to tubes 5 and
6.
5. Record the color of each aqueous (water) halogen solution in the Data
Table under column “no halide ion, before addition of halide ion.”
6. Add approximately 10 drops of hexane to each tube 1-6.
Follow safety procedures!
MCHS Chemistry
Laboratory Notes
Ms. Robinson Date:_______ Class: ____ Name:____________________
7. Place a stopper on each tube. Hold the stopper in place with a finger
and carefully invert each tube several times to mix the liquids.
8. Use the Data Table under column “none, before addition of halide ion”
to record your observations of each halogen mixture after hexane has
been added. Which layer is which? What colors are they?
Part B: Reactions of halogens with sodium halides.
9. Add 10 drops of sodium bromine (NaBr) solution to the chlorine
solution in tube 1. Replace the stopper on the tube and carefully invert
the tube several times to mix the liquids. Observe if any reaction
occurs—look for changes in color to either layer. Record all
observations in the Data Table. If no changes are apparent, write NR
for no reaction in the table.
10. Add 10 drops of the other sodium halide solutions according to the
following chart to complete the set of reactions in the tubes 2-6.
Record detailed observations after mixing the solutions in the tubes.
Complete the Data Table.
11. Dispose of the solutions in the labeled waste container in the fume
hood. Rinse the tubes in water and drain in a rack.
Post-lab questions:
A. Based on your observations, are the halogens more soluble in
hexane or water?
B. Did chlorine react with sodium bromide? With sodium iodide?
What evidence do you have for any reaction that occurred?
C. Did bromine react with sodium chloride? With sodium iodide?
What evidence do you have for any reaction that occurred?
Follow safety procedures!
MCHS Chemistry
Laboratory Notes
Ms. Robinson Date:_______ Class: ____ Name:____________________
D. Did iodine react with sodium chloride? With sodium bromide?
What evidence do you have for any reaction that occurred?
E. Write a balanced equation for each reaction using the example
below:
X2 + 2 NaY Æ 2 NaX + Y2
Where X2 and Y2 are halogens (elements). NaX and NaY are sodium
halides (ions).
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•
•
F. Based on your results, which halogen is more reactive? Least
reactive? Intermediate? Explain why this is so using the words
atomic size, electron shielding, electron affinity, nucleus, octet.
G. Assuming other nonmetals behave the same as halogens, write a
general statement about the periodic trend in the reactivity of
nonmetals as you go down a column in the periodic table.
HalogenLab.htm
Follow safety procedures!