Lab 6: CHEMICAL EQUILIBRIUM LAB
Introduction: In this experiment you will start with a reaction that is at
equilibrium. You will then change the concentrations of various ions that are
present and note the effect on the state of equilibrium. The equilibrium
reaction chosen has a colored product, so changes in its concentration can be
readily detected by a corresponding change in color intensity.
Procedure:
1. Pour about 25 mL of 0.0020 M potassium thiocyanate solution, KSCN,
and 25 mL of distilled water into a beaker.
a. What is the color of this solution? ____________________
b. What are the 2 ions in this solution? __________________
2. Look at the bottle of 0.20M iron (III)nitrate solution, Fe(NO3)3 at
your lab station.
a. What is the color of this solution? _____________________
b. What are the 2 ions in this solution? ___________________
3. Add 5 drops of the Fe(NO3)3 solution to the beaker containing the
potassium thiocyanate solution, KSCN. Gently swirl the mixture.
What is the color of this solution? _____________________
4. There are now 4 ions in this solution. What are the two combinations
of ions that could account for the color in step three?
___________________________________________
5. At your lab station there is a solution of potassium nitrate KNO3.
What is the color of this solution? _______________
What are the two ions in this solution? ______________
6. Based on your observations in step 5 and your answer to question 4,
what are the two ions that must be responsible for the color you
observed in step 5?
_________________________.
7. Pour equal amounts of the solution (from your beaker) into 4 test
tubes. Place a piece of white paper behind the test tubes to help you
determine color changes. The first test tube will serve as your
reference (control).
8. To the second test tube add 2 or 3 crystals of KSCN. Compare the
color of this test tube to the reference test tube.
__________________________
What ions are you adding when you add KSCN to test tube 2?
________________
Other experiments have shown that the ion responsible for the
color is the complex ion FeSCN2+. What can you say about the
concentration of FeSCN 2+ in test tube 2 compared to the
reference? ______________________
9. To the third test tube add 3 drops of Fe(NO3)3 solution. Compare the
color of this test tube to the reference tube.
__________________________
What ions are you adding when you added Fe(NO3)3 ?______________
What can you say about the concentration of FeSCN 2+ in test tube 3
compared to the reference? __________________?
10. To the fourth test tube add, a few at a time, 5 to 10 small crystals
of Na2HPO4. Compare the color of this test tube to the reference
tube. __________________________ What can you say about the
concentration of FeSCN 2+ in test tube 4 compared to the reference?
__________________?
What ions are you adding when you added Na2HPO4?
____________________________
Other experiments have shown that the HPO42- ion combines readily
with Fe3+ ion to produce a milky solution. What effect does adding
Na2HPO4 have on the concentration of Fe3+?___________________
What effect does adding Na2HPO4 have on the concentration of
FeSCN2+?_________________________.
11. The reaction that took place to produce the colored complex is
Fe3+ + SCN- ----> FeSCN2+
Explain the results (color changes) you observed in test tubes 2-4 using
LeChatelier’s Principle. Be specific!