Chemistry Unit 5 Topic 1 Nomenclature
LAB-CORE Formation and Decomposition of Zinc Iodide
TEKS
C.7 A
C.7 B
Name ionic compounds containing main group or transition metals, covalent compounds, acids, and bases,
using International Union of Pure and Applied Chemistry (IUPAC) nomenclature rules.
Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or
transition metals, covalent compounds, acids, and bases
KUD
Determine the oxidation number for an ion, including transition metals.
Name ionic and covalent compounds using the PT and Polyatomic Ions Chart.
Write chemical formulas for ionic and covalent compounds.
Chemistry uses formulas to express and moles to quantify matter and its interactions.
Materials
Formation and Decomposition of Zinc Iodide Lab Student Pages (1 copy per student)
Formation and Decomposition of Zinc Iodide Lab Quiz (1 copy per student)
Zinc (dust)
Iodine (crystals)
Distilled water
Weigh dishes or weigh paper (2 for each lab group throughout the day)
Balances (2)
Scoopulas (2)
Test Tubes (1 per lab group)
Stir Rods (1 per lab group)
9V Batteries (1 per lab group)
Wires with alligator clips (2 per lab group)
Nails (2 per lab group)
Petri dishes (1 per lab group)
Test Tube Racks (1 per lab group)
Test Tube Tongs (1 per lab group)
Teacher Procedure (Expected students answers are shown in italics.)
Pre-lab Activities
1. Distribute Formation and Decomposition of Zinc Iodide Lab Pages to each student at least one day in
advance.
2. Instruct students to complete the Prelab Assignment in their lab book before coming to class on lab day.
Prelab Assignment includes:
 Background Questions
 Safety
 Chemical Inventory
 Purpose
 Procedure
 Data and Observations Table
Teacher Lab Setup
1. Set up two balances in the room. One balance is for measuring zinc. One balance is for measuring iodine.
Put the chemicals by the balances with scoopulas and weigh dishes, but do not remove the lids until you
are beginning the lab.
2. Each lab group needs the following at their station:
a.
Test Tube (1)
b.
Test Tube Rack (1)
c.
Test Tube Tongs (1)
d.
A sample of distilled water
e.
Stir Rod (1)
f.
9V Battery (1)
Chemistry Unit 5 Topic 1 Nomenclature
g.
h.
i.
Wires with alligator clips (2)
Nails (2)
Petri Dish (1)
Warm-up
1. Utilize a relevant question or suitable warm-up activity to allow time for you to check the Pre-Lab
assignment.
2. Use this time to also convey to students any changes to the lab, or special instructions necessary to
facilitate student time in the lab. Special instructions should include information on carefully weighing out
zinc and iodine and the importance of not spilling them and replacing the lids when finished.
3. Ask some students these questions: (student answers will vary. Encourage some class discussion at this
point)
a. What do you think will happen when you mix zinc and iodine together? They will react. They will form
a compound. They will release energy.
b. What kind of elements are zinc and iodine? Zinc is a metal and iodine is a nonmetal.
c. What kind of compound do you think they will form and why? They will form an ionic compound
because they are a metal and a nonmetal.
d. How will the formula for the compound containing zinc and iodine be written. The formula for the
ionic compound containing zinc and iodine is ZnI2.
Lab
1. After you have asked these questions and checked student Prelab Assignments, send student groups to
assigned lab station to start the activity.
2. The teacher should carefully monitor the balances during the first 5-10 minutes of class as students are
measuring out zinc and iodine. Ensure that students do not spill the substances and that they replace the
lids when they are done measuring.
3. As students are working the teacher should be circulating the room to ensure that students are on task and
following the lab procedure. Ask the following questions.
a. What happened when you mixed the two elements together? They reacted. They released heat, the
color changed.
b. After they reacted, did you have some leftover elements? Which one was left over? The zinc.
c. If the elements reacted what did they form? A compound: zinc iodide. Where is the compound? Some
students will think it is the stuff settled at the bottom, but that is zinc. The zinc iodide is dissolved in
the solution.
d. When you put the nails in the solution, what are you seeing? Notice which nail is hooked up to the
positive end of the battery and which one is on the negative end of the battery. The nails get “dirty.”
One nail is collecting zinc and one is collecting iodine. They are separating from a compound back into
the elements.
4. At the end of the lab, give instructions to students regarding final clean-up of the lab tables. Remind
students to wash their hands before leaving the lab area. Briefly check each station to ensure students
have not removed equipment or chemicals from the lab area.
5. Instruct students to return to their seats. Lead a classroom discussion on their observations.
a. What kind of changes did you see in today’s lab? Two chemical changes, one when the elements
b.
c.
combined and one when they were separated.
Do you think the elements or the compound is more stable? The compound because it was favored by
nature. The compound took energy to separate, so the elements are more unstable.
What substances were forming on the two nails? Why do you think they separated the way they did?
The positive zinc ions were attracted to the negative nail, and the negative iodide ions were attracted
to the positive nail.
6. Explain to students that they will complete the lab for homework, including Calculations, Conclusion & Error
Analysis.
7. The Lab Quiz will be administered the day the lab is turned in. You should include the lab quiz as 30% of
the final lab grade.
Chemistry Unit 5 Topic 1 Nomenclature
LAB-CORE Formation and Decomposition of Zinc Iodide– Student Page
Name _______________________
Background:
Compounds are chemical combinations of elements. Many chemical reactions of elements to form
compounds are spectacular but must be run under special lab conditions because they are dangerous. The
reaction of sodium and chlorine to form salt is a good example. It is violently explosive! If elements react
spontaneously to form compounds, this is a good indication that the compound state is more stable than
the free element state. To break a stable compound down into its component elements, energy must be
put into the compound. Electricity is often used as this energy source, and the process is called electrolysis.
Background Questions
1. Based on their positions on the periodic table, predict and explain the reactivity of zinc and iodine. Give at
least 2 supporting facts (Clues – think about what types of elements they are and their number of valence
electrons).
2. Read the procedure and then predict how you will know a chemical change has occurred in this lab.
Provide at least 3 clues you expect to see.
Purpose: To compare a compound with its component elements; to observe and monitor a chemical reaction; to
observe the decomposition of the compound back into its elements
Safety: Wear goggles and apron. Iodine crystals are toxic and will stain skin. Reaction between zinc and iodine
releases heat; use a test tube holder.
Chemical Inventory
Chemical
Hazard
Zinc
Dust is extremely flammable.
Iodine Crystals
Toxic and will stain skin and other surfaces. Avoid contact with skin.
Procedure
1. Obtain a medium-sized test tube and Petri dish. Place the test tube upright in a test tube rack.
2. Obtain approximately 1 g of zinc dust and approximately 1 g of iodine from the weigh stations.
3. Carefully add the 1 g of zinc dust and about 10 mL of distilled water to the test tube.
4. Carefully add about 1 g of iodine to the test tube. Record your observations in your table.
5. Stir the contents of the test tube thoroughly with a stirring rod until there is no more evidence of a
reaction. Record any observations of physical or chemical change.
6. Allow the reaction mixture to settle. Using the test tube tongs, carefully pick up the test tube and pour off
the solution phase (liquid only) into the Petri dish.
7. Add about 15 mL of water to the Petri dish.
8. Obtain a 9-V battery, two wires with alligator clips, and two nails. Attach one nail to one clip of each wire
and attach the other end of the wires to the two prongs of the battery. Make sure the wires and nails do
not touch each other.
9. Dip the wires into opposite sides of the Petri dish and observe what takes place. Record your
observations.
10. After two minutes, remove the wires from the solution and examine the wires. Again, record your
observations.
11. Disconnect the battery, wires, and nails. Rinse the nails with water and pat them dry. Clean your lab
station.
Chemistry Unit 5 Topic 1 Nomenclature
Data and Observations: Copy this table into the Data and Observations section of your lab report.
Step of the Procedure
4
Observations
5
9
10
Calculations & Analysis: None
Conclusion
Your conclusion should discuss the points of the purpose. Compare the elements zinc and iodide with the
compound that formed. How did you know a chemical reaction was happening? When was the compound forming
and when was the compound decomposing? Why did you have to use the battery?
Sources of Error: What could have led to incorrect or unclear observations?
Chemistry Unit 5 Topic 1 Nomenclature
LAB-CORE Formation and Decomposition of Zinc Iodide– Teacher Page
Student responses in red.
Background Questions
1. Based on their positions on the periodic table, predict and explain the reactivity of zinc and iodine. Give at
least 2 supporting facts (Clues – Think about what types of elements they are and their number of valence
electrons). Zinc is a metal and iodine is a nonmetal, so they should form an ionic compound. Zinc has two
valence electrons and iodine has 7, so zinc wants to lose electrons, and iodine wants to gain electrons.
2. Read the procedure, and then predict how you will know a chemical change has occurred in this lab.
Provide at least 3 clues you expect to see. The reaction will give off heat. The reaction will change colors.
Electricity is necessary to separate the compound.
Data and Observations:
Step of the Procedure
4
5
9
10
Observations
Iodine turns water brownish, but then it begins to react with zinc. Begins to give off
heat and change colors.
When stirred, the elements react more fully, and the brownish color fades completely
as the iodine reacts. The excess zinc falls to the bottom.
The nails begin to change in appearance. One seems to grow, and one has small
bubbles forming or a brownish cloudy liquid forming around it.
One nail is “larger” since it has been coated with zinc. The other appears the same.
Calculations & Analysis: None
Conclusion
Student answers will vary. Check that students have answered all the questions posed in the prompt.
Sources of Error
Student answers will vary. Check that students have answered all the questions posed in the prompt.
Chemistry Unit 5 Topic 1 Nomenclature
LAB-CORE Formation and Decomposition of Zinc Iodide Quiz
Name ________________________
1. Why do you think the reaction between zinc and iodine stopped?
2. Was the reaction between zinc and iodine endothermic or exothermic?
3. What evidence do you have that the compound was decomposed back to its elements by electrolysis?
4. Is zinc iodide an ionic or covalent compound? How do you know?
5. What would be different in this reaction if water was not used?
6. Write the formula for zinc iodide.