Equilibrium Lab
Equilibrium System #1
1. Half fill a test tube with 1.5 M copper(II) chloride, CuCl2 solution.
2. Divide so five tubes contain approximately equal volumes. Equilibrium has
already been established in the solution.
Chemical Equation for the Equilibrium
CuCl42-(aq) + 4 H2O(l)
Green soln Colorless
Cu(H2O)42+(aq) + 4 Cl-(aq) + heat
Light blue soln Colorless
Disturbing the Equilibrium
1. To Tube 2 add a small quantity (the size of a rice grain) of solid calcium
chloride, CaCl2. Mix to dissolve the solid. Repeat the addition and
dissolving of solid CaCl2 until no more solid will dissolve. Record results.
2. To Tube 3 add enough ethyl alcohol, C2H5OH, to triple the volume of the
solution. Mix, observe, and record.
3. Place Tube 4 in a hot-water bath. Observe and record.
4. Place Tube 5 in an ice-water bath. Observe and record.
Observations:
Test Tube #
1
Contents
Addition of
Observation
2
3
4
5
Discussion points: What is happening to equilibrium during these changes?
Which way does it shift and why, how do you know?
Are the reactions reversible and why?
What equilibrium expressions are involved?
How do you know where the equilibrium is shifting upon additions?
Equilibrium System #2
Many reactions either consume or produce heat. Complex ion formation is an
example of such a process. In this experiment you will determine if a specific
complex ion formation if endothermic or exothermic.
In aqueous solution, cobalt ions are solvated by six water molecules making a
complex ion [Co(H2O)6]2+. If excess chloride is added, a blue chloride complex
forms [CoCl4]2[Co(H2O)6]2+ + 4Cl- ⇋
[CoCl4]2- + 6H2O
You will determine whether this reaction is exothermic or endothermic.
Procedure:
1. Add 3 mL of 1.5 M CoCl2 in a test tube
2. In a fumehood, add conc. HCl dropwise until the solution turns a purpleviolet colour (this indicates both complexes are present)
3. To each of three test tubes, add 1 mL of the solution
4. Place one in a hot water bath, describe the change
5. Place one in an ice bath, describe the change
6. Keep the last as a control
7. Switch the test tubes in the hot water bath and cold water bath and
observe
Observations:
Test tube
#
1
Contents Change
Induced
Observations
2
3
Discussion Points: Is the equilibrium endothermic or exothermic, how do you
know?
Show the equilibrium expression including heat and write the Kc expression
If we diluted the system (i.e. increased the volume) explain the shift that would
result. How would you prove this is correct?
How will K change if increase the temperature? Explain.
Equilibrium System #3
Bromothymol blue is a weak organic acid with a complex formula. For our
purpose, its formula can be abbreviated to HBb.
1. Half-fill three test tubes with distilled water.
2. Add three drops of bromothymol blue indicator to each tube. Mix
thoroughly.
HBb(aq)
Yellow
H+(aq)
+ Bb-(aq)
Colorless
Blue
(Green can be observed if approximately equal amounts of yellow and blue forms
are present.)
Disturbing the Equilibrium
1. To Tube 2 add two drops of 0.1 M hydrochloric acid, HCl, and mix.
Observe and record.
2. To Tube 3 add two drops of 0.1 M sodium hydroxide, NaOH, and mix.
Observe and record.
3. Explore what happens when you now add NaOH to Tube 2 or HCl to Tube
3. See whether your observations are in agreement with observations you
have already recorded.
Observations:
Test tube
#
1
Contents
Addition of:
Observations
2
3
Discussion points: Where does the equilibrium shift on each addition? How do
you know?
What happens to K if you add acid? Base? Explain.
What colours did you observe? What pH are these representative of?