Establishing Equilibrium
Objective: Students will establish a system at equilibrium.
Materials: (2) 25 mL graduated cylinders, 2 straws w/different diameters,
food coloring, safety glasses
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 cylinder with water to the 25.0 mL mark.
3) Place the forward straw into the reactant cylinder so that it
touches the bottom. Place the reverse straw in the empty product
cylinder.
4) Put your finger over the top of the forward straw so that the liquid
is trapped in the 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 on the next
page. 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 25.0 mL of
colored water in the product cylinder and nothing in the reactant
cylinder. Use the same straws for the forward and reverse
reactions.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Data Table
Trial 1
Transfer
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Reactant mL
Product mL
Trial 2
Transfer
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Reactant mL
Product mL
Analysis and Conclusion
1) Did you use the large straw for the forward or reverse reaction?
2) At equilibrium, was there a greater volume of products or reactants?
3) What was the effect on equilibrium volumes when you started with no
reactants and 25.0 mL of products?
4) Using Excel prepare a graph for that shows your results for both trials by
plotting the transfer number on the x-axis and the volumes for both
reactants and products on the y-axis.
This lab is a modification from Prentice Hall’s Connections to Our Changing World.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright