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Hour:
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ESTABLISHING EQUILIBRIUM
Problem: How can you determine when a system is at equilibrium?
Materials: 2 10 mL graduated cylinders
food coloring
2 drinking straws with different diameters
graph paper
paper and pencil
Procedure:
1) Label one graduated cylinder “Reactants” and the other “Products”. Label one
straw “Forward” and the other “Reverse”.
2) Add a few drops of food coloring to the REACTANT cylinder. Then fill the
REACTANT cylinder with water to the 10.0 mL mark.
3) Place the forward straw into the reactant cylinder. Place the reverse straw in the
empty product cylinder.
4) Put your finger over the top of the forward straw. Transfer the colored water in
the straw to the product cylinder.
5) Now put your finger over the reverse straw and transfer colored liquid from the
product cylinder to the reactant cylinder.
6) Record the volume of each cylinder in the data table. Each time you transfer
liquid from the reactant cylinder to the product cylinder and back from the
product cylinder to the reactant cylinder constitutes one transfer.
7) Repeat steps 4,5, and 6 until the volumes in the cylinders remain constant for at
least 5 readings.
8) Repeat the entire experiment, but this time begin with 10.0 mL of colored water in
the product cylinder and nothing in the reactant cylinder. Use the same straws for
the forward and reverse reactions.
Data Table:
Experiment #1
Transfer
1
2
3
4
5
6
7
8
9
10
Reactant Cylinder (mL)
Experiment #2
Transfer
1
2
3
4
5
6
7
8
9
10
Volume
Product Cylinder (mL)
Volume
Reactant Cylinder (mL)
Product Cylinder (mL)
Observations:
1) Did you use the larger straw for the forward or reverse reaction? Circle
2) At equilibrium, was there a greater volume of products or reactants? Circle
3) What was the effect on equilibrium volumes when you started with no reactants
and 10.0 mL of products?
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4) Graph your results on the graph paper for both experiments by plotting the
transfer number on the x-axis and the volumes for both reactants and products on
the y-axis.
Analysis:
1) Was equilibrium established in both experiments? Circle
YES or NO
2) What can you conclude from your answer in #1?
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3) What variable determined whether there was a greater volume of reactants or products
at equilibrium? _____________________________________________
4) Repeat this experiment starting with a portion of the 6.0 mL of colored water in one
cylinder and the remaining 4.0 mL amount in the other cylinder.
Experiment #3
Transfer
1
2
3
4
5
6
7
8
9
10
Volume
Reactant Cylinder (mL)
Product Cylinder (mL)
What did you learn about the equilibrium in the third experiment?
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