CHEM 10
Brakke
ECA – Topic 03
T03D04 – Periodicity in Group 7A: The Halogens
Name………………………………………………..
9
PRE-LAB DISCUSSION:
How are non-metals reactive?
What direction does their trend go? Why?
When a non-metal reacts, what does it do? What form will it then be in (element, compound, ion, etc)?
If two halogens are competing to become negatively charged, who will win?
In the following equation, only one halogen can be in solution (aqueous – aq) at any given time, the other must be a gas,
liquid or solid precipitate. The most reactive will become an ion in solution.
Cl2 (g) + 2I (aq)  2Cl (aq) + I2 (s)
Before the reaction:
• Each Cl has 7 electrons of its own, and sharing one more
• Each I has a total of 8 electrons as they are I
After the reaction:
• Each Cl has 8 electrons as they are now Cl
• Each I has 7 electrons of its own, and sharing one more
Research Question / Purpose
How can unknown solutions of sodium halides be identified based on their known (and tested) reactivity? To be able to
develop a set of procedures that will allow you to address this question. Justify your work using chemical explanations and
your data.
F
17
Cl
35
Br
53
I
85
At
117
EQUIPMENT
Well plate, safety glasses, pipet dropper, test tube rack, test tubes
MATERIALS
0.1M solutions of : NaF, NaCl, NaBr, NaI Ca(NO3)2 AgNO3
Cyclohexane
chlorine water
3.0M NH3 (aq)
PROCEDURE
Part I:
1. Using a clean well plate (and a piece of paper to label) add 1-2 drops of one of the halide solutions, adding a different solution to
each of four different wells:
2. Add 2-3 drops (with a pipet) of 0.1M Ca(NO3)2 to each solution. Record your observations.
3. To a new set of wells, add a 1-2 drops of one of the halide solutions to a new set of wells, adding a different solution to each of
four wells again.
4. Add 2-3 drops (with a pipet) of 0.1M AgNO3 to each solution.
5. Only to each solution in which precipitate form (from Part 4) add about 2-3 drops (with a pipet) of 3.0M NH3 (aq). Record your
observations.
Part II: Complete in the fume hood with group
6. Add about a mL each of the following solutions to 3 clean test tubes (NOT IN YOUR WELL PLATE)
Tube 1: 0.1M NaF
Tube 2: 0.1M NaBr
Tube 3: 0.1M NaI
7. To each solution, add 1mL of cyclohexane. Record your observations.
8. Add 5 drops of chlorine water to each test tube of step 6&7. Stopper, AND cover with a paper towel and shake each tube gently.
Record your observations.
CAUTION:
*After putting the stopper on your tube, cover with a piece of paper towel*
Part III:
9. Clean your well plate
10. Have a partner place 2-3 drops of the same solution (of their choice – they should not tell you as it’s an unknown) to three wells
in your plate
11. Determine the identity of your unknowns.