Aim: To study the equilibrium system and their responses to stress as described by Le Chatelier’s
principle.
Procedure:
1. Using a marking pencil, number four test tubes 1 through 4 and stand them on a test tube rack.
2. Measure out 5ml of 0.1M FeCl3 and pour it into a 100-ml beaker. Add 5ml of 0.1M KSCN to the
same beaker. Dilute the content of the beaker w/ distilled water until the solution is a light
reddish-orange color. Divide the solution equally among the four test tubes. Set test tube 1 at
one end of the rack to be used for color comparison.
3. Using a dropper pipette, add 0,1M FeCl3 drop by drop into the solution in test tube2 until a
color change occurs. Record your observation in part A of “Observations and Data.” Rinse the
pipette.
4. Repeat step 3, but instead of FeCl3, add the following solutions drop by drop to the test tube
indicated. Rinse the pipette after each use. Test tube 3
0.1M KSCN. Test tube 4 0.1M
KCl
5. Discard the solutions. Wash and rinse the test tubes and invert them in the rack to drain
6. Using a marking pencil, number four test tubes 5 through 8. Stand them on the rack.
7. Measure out 5 ml of 0.1M K2CrO4 into test tubes 5 and 6. Rinse the graduates cylinder and
measure out 5 ml of 0.1M K2Cr2O7. Divide this equally between test tube 7 and 8.
8. Using a dropper pipette, add 0.1M HCl drop by drop to test tube 5 until the color changes.
9. Repeat step 8 with test tube 6. As soon as the color changes, rinse the pipette and use it to
add 1.0M NaoH drop by drop until the color changes again.
10. Using the pipette, add 1.0 M NaOH to test tube 7 until color changes.
11. Repeat step 10 with test tube 8, As soon as the color changes, Rinse pipette and use it to add
1.0 M HCl to the solution until the color changes again.
Observations and Data:
Part A
Test Tube Number
#1
#2
#3
#4
Color
Orange color
Dark orange color
Red-orange color
Light orange color
Part B
Test Tube Number
#5
#6
#7
#8
Color
Orange color
Darker yellow color
Yellow color
Darker orange color
Conclusions and Questions:
1. Write equilibrium equations for the reversible reactions that take place in Part A and Part B.
a) FeCl3 + 3KSCN
Fe(SCN)3 + 3KCl
b) FeCl3 + 3KSCN
Fe(SCN)3 + 3KCl
c) FeCl3 + 3KSCN
Fe(SCN)3 + 3KCl
d) K2CrO4 + 2HCl
H2CrO4 + 2KCl
e) K2CrO4 + 2NaOH
Na2CrO4 + 2KOH
f) K2Cr2O7 + 2HCl
H2Cr2O7 + 2KCl
g) K2Cr2O7 + 2NaOH
Na2Cr2O7 + 2KOH
2. Using Le Chatelier’s principle, explain how the addition of FeCl3 to the solution in test tube 2(step3)
affected the equilibrium that existed in the solution. Give similar explanations for the addition of
each of the other substances (step4).
The addition of FeCl3 to the equilibrium system caused an increase of the concentration of
FeCl3 thus causing the rate of the forward reaction to increase.
3. Using the equailibrium equations for the reaction and Le Chatelier;s principle, explain the color
change noted in part B.
The color changes in part B was due to and increase of concentration to one side of the
reaction causing an increase in the stress. To relieve the stress the reaction shifted from one side
to the other.