Chemistry 10
Brakke
ECA – Topic D
TDD02 – Periodicity in Group 7A: The Halogens
Name………………………………………………..
9
PRE-LAB DISCUSSION:
The elements in group 7A of the Periodic Table are called the halogen family. Like the elements in groups 1A (Alkali Metals)
and 2A (Alkaline Earths), the members of the halogen family are too reactive to be found in nature as free elements to any
great extent. In elemental form, halogens exist as covalently bonded diatomic (two-atom) molecules such as F2, Cl2, Br2 and
I2. During chemical reaction, halogens ionize to form ions. These ions are known as halide ions, or simply halides.
Unlike the elements in groups 1A and 2A, the halogens are active nonmetals. That is, they show a strong tendency to accept
electrons during chemical reactions. This chemical activity decreases as you move down in the group. This trend may be
seen in reactions between halogens and halides. A more active halogen will “take away” electrons from the halide of a less
active member of the group, as illustrated in the following “equation”:
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
In this reaction, elemental chlorine forms halide (chlorine) ions by taking electrons away from the ions of less active halogen
iodide. The iodine atoms thus produced combine to form diatomic iodine molecules. This shows that Chlorine is more
reactive than Iodine. The general formula for such reactions is,
A2 + 2B  2A + B2
(where A is always a more active halogen than B.)
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-
-
F
17
Cl
35
Br
53
I
85
At
117
-
Halides in solution can be separated by differences in solubility of certain metallic salts. If the ions F , Cl , Br , and I are all present in
an aqueous solution, they can be separated by adding metallic ions to form an insoluble salt (CaF2) which will precipitate out of
+
solution. The other three halides will not. However, Cl , Br , and I will all react with Ag ions to form salts that are insoluble in water.
These salts may be distinguished from one another by differences in their solubility in ammonia water, NH3 (aq).
In this experiment you will observe some reactions of the halogens and will verify some of the properties of these substances
discussed above.
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.
EQUIPMENT
Test Tubes (4)
Test Tube Rack
Stoppers, for test tubes
pipet dropper
safety glasses
MATERIALS
0.1M solutions of : NaF, NaCl, NaBr, NaI Ca(NO3)2 AgNO3
Cyclohexane
chlorine water
3.0M NH3 (aq)
PROCEDURE
Record all observations and results in the Observations and Data section.
Part I:
1. Using a clean micro wellplate and a piece of paper to label add a few mL of one of the following solutions, adding a different
solution to each of four different wells:
Tube 1: 0.1M NaF
Tube 2: 0.1M NaCl
Tube 3: 0.1M NaBr
Tube 4: 0.1M NaI.
2. Add 2-3 drops (with a pipet) of 0.1M Ca(NO3)2 to each solution. Record your observations.
Chemistry 10
Brakke
ECA – Topic D
3. Add a few mL of one of the following solutions to a new set of wells, adding a different solution to each of four wells again.
Tube 1: 0.1M NaF
Tube 2: 0.1M NaCl
Tube 3: 0.1M NaBr
Tube 4: 0.1M NaI
4. Add 2-3 drops (with a pipet) of 0.1M AgNO3 to each solution. Note the formation of precipitates.
5. Only to each solution in which precipitates form add about 10 drops (with a pipet) of 3.0M NH3 (aq). Record your observations.
Part II:
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. Obtain a letter-coded “unknown” solution. Note the letter of your “unknown” in your observations
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-
- -
10. The “unknown” solution contains the sodium salt of one of the halide ions (F ,Cl ,Br ,I ).
Using what you learned in Parts 1 and II, write out a sequence of steps needed to identify your “unknown” halide. Use quantities
indicated in previous parts of in previous parts of this experiment. Check your proposed sequence with Mr. Brakke before proceeding.
Make all suggested corrections.
11. Using your corrected sequence of steps, identify the “unknown” halide ion. Remember to follow the CAUTION instruction listed
in Part II. Record your results.
12. Trade your unknown with another student in the class. Repeat steps 9-11 for that solution. Do this until you have a total of 4
different unknown numbers tested.
PRELAB:
Write your predicted balanced chemical equation for the reaction of each sodium halide (F, Cl, Br, I) reacting with both calcium
nitrate and silver nitrate.
Write your predicted balanced chemical equation for the reaction of each sodium halide (F, Cl, Br, I) with chlorine (Cl2). If no reaction
should occur, simply write NVR (No Visible Reaction) on the products side of the reaction.
Based on your knowledge of the periodic trend in reactivity of non-metals, rank the four halides (F, Cl, Br, I) in order of reactivity.
Make a statement in terms of which halides will be replaced by each halogen. Support using equations for each.
OBSERVATIONS AND DATA
Using excel or a word document, create a data table that will allow to collect and organize the proper data for your laboratory
experiment. Once you have collected and organized data from Part I & II, you can develop a method for collecting data. Finally you
can conclude and present your report – typed and organized in a word document (10pt Font, single spaced).
Recording Raw Data
C P N n/a • Table 2 given values/ formulas/ Unk’s/
C P N n/a • Prelab
C P N n/a • Table 3 containing raw quantitative data
C P N n/a • Table 4 qualitative observations
C or Zero • All data is collected individually (nonnegotiable)
C P N n/a • Tables contain
•
Title
•
Headings
•
explanations
C P N n/a • Units are present and correct throughout
C P N n/a • Tables are organized and easy to follow
Concluding (in words)
C P N n/a • Results are repeated at
beginning
C P N n/a • Response to research question
C P N n/a • Literature values are referenced
•
using MLA for source
C P N n/a • Describe the chemistry
C P N n/a • JUSTIFICATION of results
C P N n/a • Conclusion is based on your
results
Developing a Method for Collecting Data
C P N n/a • Procedure is detailed, easy to
repeat
C P N n/a • Materials list is complete
C P N n/a • ID Independent Variables
C P N n/a • ID Dependent Variables
C P N n/a • Picture (or drawing) of
apparatus – Diagram of well plate
C P N n/a • Collection of Data (explanation
or table)
Chemistry 10
Brakke
ECA – Topic D