Equilibrium
Le Châtelier’s Principle Labs
Name_________________________
Per_____Date__________________
In your lab notebook, record the materials and procedure on the left half of the page, and your
analysis, discussion and conclusions on the right hand side.
Blue Bottle Lab: Disruption of Equilibrium.
Concepts to investigate: Reactions, oxidation, reduction, equilibrium
Materials: Flask, stopper, potassium hydroxide (KOH), methylene blue, glucose (dextrose), 100 mL graduated
cylinder, scoop, balance
In this activity, when a bottle containing a colorless solution is shaken, the solution turns blue, but when allowed
to stand, it becomes colorless. At equilibrium the solution is colorless, but when equilibrium is disrupted by the
addition of oxygen with shaking, it departs from equilibrium and becomes blue.
Note: Methylene blue is blue when it is oxidized, colorless when reduced.
Procedure: Prepare the solution by adding 2 grams of potassium hydroxide (KOH) to 100 mL of distilled water
in a bottle. Allow to sit for one minute and then dissolve 2.5g of glucose (dextrose). Use a dropper bottle and
add 2-3 drops of methylene blue indicator. Close the bottle, shake and swirl, and the solution should turn blue.
After standing, the solution should turn colorless. After it has turned colorless, remove the stopper, pick it up
and shake it. Note the color of the solution.
Explain in your own words what is happening to the equilibrium in this reaction.
a) adding oxygen  what happens, and b) allowing bottle to sit
Cobalt(II) chloride and the effect of temperature on equilibrium
Concepts to investigate: equilibrium constant Keq, temperature, dynamic equilibrium
Materials: Cobalt(II) chloride prepared for you, test tubes, hot water bath, ice bath
For each chemical system there is a relationship among the concentrations of reactants and products that
describes the relative proportions of each at equilibrium. A balanced chemical equation for the system is
necessary when determining this relationship. Cobalt(II) forms a complex ion with water.
Rxn (I)
Heat + Co(H2O)62+ (aq) + 4 Cl- (aq)  CoCl4-2 (aq) + 6 H2O(l)
pink
blue/purple
Procedure: The solution has been prepared for you. Divide the solution into 3 test tubes with approximately 5-6
mL in each. Keep 1 test tube at room temperature to serve as a control, TT2 in an ice bath, and TT3 in a hot
water bath at about 60˚C. After ten minutes, switch the TT2 and TT3 to see if you can reverse the shift in
equilibrium.
Explain in your own words what happens when the solution is cooled and what happens to the equilibrium when
the solution is heated. What happens to the color?
Write the Kc expression for the above Reaction (I). Explain how changing the numerator or denominator
changes the value of Kc for Reaction (I).
Kc =
1
Equilibrium
Le Châtelier’s Principle Labs
Name_________________________
Per_____Date__________________
Ammonia + phenolphthalein
Materials: HH ammonia in dropper bottle, phenolphthalein in dropper bottle, test tube, test tube rack, hotplate,
beaker with tap water, thermometer
Reaction (II)
NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
Procedure: Dilute household ammonia 1 to 20 with water - put 2 to 3 drops into a test tube, then add enough
distilled water to fill the test tube halfway. Add a drop of phenolphthalein and note that the solution turns pink.
Place the TT with this solution into a hot water bath at a temperature above 60˚C. Observe the color change over
time.
Write the Kc for this reaction: Kc =
Phenolphthalein turns _______________ when in the presence of a base (OH-).
Explain in your own words what happened to the equilibrium when placed in the hot water bath for 5-10 min.
What is the evidence for this shift? What does this change mean to the Kc value?
Is Kc for this reaction temperature dependent? Justify your answer.
Chromate-Dichromate Equilibrium
Materials: 5 mL 0.1 M K2CrO4, 5 mL 0.1 M K2Cr2O7, 1 M HCl, 1 M NaOH, 2 test tubes, test tube rack
Procedure:
1. Fill a test tube approximately half-full with potassium chromate, K2CrO4 (Tube 1).
2. Fill another test tube approximately half-full with potassium dichromate (Tube 2).
3. To Test Tube 1 add several drops of HCl. HCl is an acid; adding HCl increases the concentration of
H3O+ ions in the equilibrium system. Note the color change.
4. After recording the color change in Test Tube 1, add several drops of NaOH. NaOH is a base; adding a
base decreases the concentration of H3O+ ions in the equilibrium system. Record the color change.
5. To Test Tube 2 add several drops of NaOH until a color change is observed.
6. After recording the color change, add several drops of HCl to Test Tube 2. Again note the change in
color.
Use Le Châtelier’s Principle to explain the color changes observed in both test tubes with the addition of both
HCl and NaOH. Write your answer as a clear, descriptive paragraph.
Reaction (III)
2 CrO42-(aq) + 2 H3O+ Cr2O72-(aq) + 3 H2O(l)
yellow
orange
2