ALL IN THE FAMILY
A Study of the Halogens
The purpose of this lab is to investigate the “reactivity” of three elements in the halogen family; chlorine,
bromine and iodine. The “reactivity”, for the halogens, refers to their ability for the neutral atom to yank an
electron off of another atom. You will be pairing up three of the halogens, and determining which halogen is the
strongest at pulling an electron off of the others.
To do this you will be using chemicals that must be handled with great care. Solutions of Cl2, Br2 and I2 are
quite toxic and caustic. Any horse play during this lab will be dealt with accordingly.
The three halogens we will be working with are in two different “forms”. Either they are in their neutral
“diatomic” state (Cl2, Br2 and I2 ), or they are in the form of ions (Cl-1, Br-1 and I-1 ). The ionic forms will be
supplied by the solutions of KCl, KBr and KI. The potassium (K) does not take part in any of the reactions in
this lab.
Prelab Questions: (You may need to read through the lab to answer all of these. So get to it!)
1) Why are the halogens more stable in their ionic form?
2) Why are the halogens so reactive in their neutral state?
3) Which layer do ions prefer?
4) Which layer do the neutral, diatomic atoms prefer?
5) If the following substances had a choice, which layer would they go to, water or hexane?
K+1, Br-1, Cl2, I2, Cl-1, I-1, Br2
6) Fill in the top row of the third chart: What is present in each mixture at the start?
PART 1 - DETERMINING THE COLORS
The purpose of this part of the lab is to see what colors the three halogens, in both their neutral and ionic
forms, are when they are in water, as well as in hexane. It is important for you to understand at this point, that a
solution of “KCl” is really a solution of K+1 ions and Cl-1 ions. Solutions of KBr and KI are split up in the same
manner.
1) To determine the colors of the halogens when they are in water, all you have to do is look at the solutions!
Since the solutions are made with water, they are already in water! Observe and record the colors of the
solutions KCl, KBr, KI, Cl2, Br2, I2. Fill in the top row of the first chart.
2) Put 3 drops of each of the solutions in a separate test tube along with 6-8 drops of hexane. Hexane is a
different kind of molecule than water, and will not mix with water. Much like oil and water. So you will see two
separate layers of liquid, one on top of the other. (It helps to tilt the test tube to see the two layers.)
To determine which layer is which, take one of the tubes and add a bit of tap water and observe which layer
increases. Once you have determined which layer is on top, this is how it will always occur.
You will find that a few of the tubes will have a colored hexane layer. This is because the neutral forms of the
halogens, when exposed to both water and hexane, will go to the hexane layer. On the other hand, the ionic
forms will go to the water layer. Observe and record the color that each species (Cl2, Br2, I2, Cl-1, Br-1, I-1)
make in the hexane layer.
3) Empty the tubes down the sink with a lot of water, and rinse them.
PART 2 - STUDY OF THE HALOGENS
4) REACTIONS WITH IODINE
Take three test tubes and add 8-10 drops of hexane and 5 drops of iodine water to each.
Now add 5 drops of KCl to one, 5 drops of KBr to another, and 5 drops of KI to the last.
Cork the three tubes and mix them. Record the colors of each layer.
Empty the tubes down the sink with a lot of water, and rinse them.
5) REACTIONS WITH BROMINE
Take three test tubes and add 8-10 drops of hexane and 5 drops of bromine water to each.
Now add 5 drops of KCl to one, 5 drops of KBr to another, and 5 drops of KI to the last.
Cork the three tubes and mix them. Record the colors of each layer.
Empty the tubes down the sink with a lot of water, and rinse them.
6) REACTIONS WITH CHLORINE
Take three test tubes and add 8-10 drops of hexane and 5 drops of chlorine water to each.
Now add 5 drops of KCl to one, 5 drops of KBr to another, and 5 drops of KI to the last.
Cork the three tubes and mix them. Record the colors of each layer.
Empty the tubes down the sink with a lot of water, and rinse them.
7) Clean your area and return the materials as directed.
PART 1 - DETERMINING THE COLORS
KCl
KBr
KI
Cl2
Br2
I2
color in hexane
color in water
PART 2 - STUDY OF THE HALOGENS
I2 + KCl
I2 + KBr
I2 + KI
Br2 + KCl
Br2 + KBr
Br2 + KI
Cl2 + KCl
Cl2 + KBr
Cl2 + KI
I2 + KBr
I2 + KI
Br2 + KCl
Br2 + KBr
Br2 + KI
Cl2 + KCl
Cl2 + KBr
Cl2 + KI
hexane
water
halogen
in hexane
Summary Chart:
I2 + KCl
before
reaction
after
reaction
QUESTIONS / CONCLUSIONS
1) What color is each of the halogens (Cl2 , Br2 , I2 ) responsible for in the hexane layer? (Use
the first chart.) Use this information to determine the halogen that is in each of the hexane
layers in part 2. Write the answers on the lines below the second chart. (Either Cl2, Br2, or I2)
2) Consider your observations, and fill in the bottom of the “Summary Chart”.
3) List the three halogens in order of most forceful at taking electrons to least forceful. Explain
how the lab shows this. (Where do you think the other two halogens fit in with this order?)
4) Explain how and why the shielding effect accounts for the order in number 4.
5) Explain how and why the size of the atom accounts for the order in number 4.
6) How does the shielding effect, and the size of the atom account for the reactive trend of the
alkali metals? (That is, the fact that they get more reactive as you go down the group, as
opposed to the halogens which get more reactive as you go up the group.)