Experiment 10
Periodic Properties of the Elements
This experiment allows you to examine the elements and to predict periodic trends. You will first examine samples of different elements and make observations based on color, state of matter, etc. to characterize them. For your experimental section, you will do experiments and come to conclusions about elements in the groups you are examining. For the halogen part of the experiment (performed during the first day) you will determine the order of oxidizing strength of the different halogens.
The Halogens - Group VIIa
In this part of the experiment, you will use six solutions (containing either a halogen or a halide salt), and an organic solvent for this part of the experiment. You will need to acquire 5-10 mL of each solution (KCl(aq), KBr(aq), KI(aq), Cl2 water, Br2 water, and I2 water). To estimate the amount of each solution, use your graduated cylinder to measure out 10 mL of water and pour it in a large test tube. Note the amount of liquid present, and then take less than this amount of each of the solutions, putting the solutions in labelled large test tubes. You will also need about 10 mL of hexane. Take only the amount of chemical you need.
Solutions containing the halide salts (KCl, KBr, and KI) are always colorless. When the halogens (Cl2, Br2, I2) are dissolved in water, a color may be present, but it may not be the characteristic color shown below. The true color of these halogens will be evident only when viewed in the hexane phase. The color of the halogen in the hexane phase, in particular, is given in the table below. Do not pay much attention to the color of the aqueous solution.
| Halogen | Color in water | Color in hexane | List the color of the hexane layer you observe |
| Cl2 | pale, yellow green | yellow green (not orange) | |
| Br2 | reddish | reddish or yellowish orange | |
| I2 | colorless to violet | violet (pinkish) |
In order to see the colors that these halogens have when dissolved in hexane, do the following experiment. Add about 1 mL (no more) of each halogen solution (i.e., the Cl2 water, Br2 water, and I2 water) to separate small test tubes. Carefully pour about 0.5 mL of hexane to each of the test tubes containing the halogen solutions (since the hexane is less dense than water it will float on top). Mix the contents of each tube and observe the color produced in the top hexane layer. Use these tubes for color comparisons.
Please also be careful not to confuse the color of chlorine (which would be yellow, but with a greenish tinge) and the color of bromine (which might be yellowish looking, but with an orange tinge to it). Also, only pay attention to the hexane layer. Look at the hexane layer horizontally, at eye level; do not pay any attention to the lower, aqueous layer, only the top hexane layer.
Before you can interpret the results of your experiments, you need to understand the following information.
Based on the example described above, if a reaction occurred, the halogen you started with (Cl2 in this example) is the stronger oxidizing agent (I2 would be the weaker oxidizing agent). On the other hand, if no reaction occurred, then the halogen you started with (Cl2 in this example) would be the weaker oxidizing agent.
You must do the experiment yourself to determine your results. However, please remember that if there is a reaction the halogen you started with be the stronger oxidizing agent. (The oxidizing agent takes an electron from the reducing agent. The oxidizing agent gets reduced, and the reducing agent gets oxidized.) The halide (which loses an electron) becomes a halogen. The halogen you start with becomes a halide when it gains an electron. Do not confuse the terms of halogen and halide. The halogen is element (e.g., Cl2, Br2, or I2) and the halide is the ion (e.g., Cl-, Br- or I-). During a reaction, the ion gets oxidized (it loses an electron) to become element, and the element gets reduced to become an ion.
Set up your experiment as follows:
Tube number |
Potassium halide solution |
Halogen water |
Color of hexane layer after mixing |
1 |
KBr(aq) |
Cl2 water1 |
|
2 |
KI(aq) |
Cl2 water1 |
|
3 |
KCl(aq) |
Br2 water |
|
4 |
KI(aq) |
Br2 water |
|
5 |
KBr(aq) |
I2
water |
|
6 |
KCl(aq) |
I2 water |
|
| 1After you have added the Cl2 water to the first two tubes, mix them throughly. Now, observe the color of the upper hexane layer. Since you added Cl2 water, if no reaction occurred, you would expect the hexane layer to turn yellow-green, which is the color of Cl2. If there is a color change, then a reaction occurred. For example, if tube #1 has a yellow-orange hexane layer, then Br2 was produced, and the Cl2 was converted into the chloride ion (Cl-). This implies that Cl2 is a better oxidizing agent than is Br2. Use this same logic for analysis of each tube, after the addition of the Br2 and I2 water solutions. | |||
Based on the observations above, predict the order for oxidizing agent. Remember, if there is a reaction (i.e., if the final hexane color is different from the halogen you started with), then the halogen is a better oxidizing agent (it takes the electron from the halide ion), and becomes an ion itself; the original halide ion (after the loss of its electron) becomes a halogen.
Strongest Oxidizing Agent: __________ > __________ > __________ Weakest Oxidizing Agent
Now, looking for periodic trends, show where you would predict F2 would be located:
Strongest Oxidizing Agent: __________ > __________ > __________ > __________ Weakest Oxidizing Agent
Activity of metals
|
Group 1A |
Group 2A |
Transition Metals |
Group 4A |
Group 5A/6A |
Elements |
|
|
|
|
|
Reactant |
HOH |
HOH |
|
|
O2 |
Acid |
|
HCl |
HCl |
HCl |
|
Based on reaction rates, make a list for the following metal elements that ranks them based on their activity.
Rank the following elements: K, Na, Mg, Ca, Mn, Fe,cCu, Zn
Most active: _____ > _____ > _____ > _____ > _____ > _____ > _____ > _____ > Least active
Go To Experiment:
1 2 3
4 5 6
7 8 9
10 11 12
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