Equilibrium
Le Chatelier’s Principle Labs
Name_________________________
Per_____Date__________________
Blue Bottle Lab: Disruption of Equilibrium.
Concepts to investigate: Reactions, oxidation, reduction, equilibrium
Materials: Flask, stopper, potassium hydroxide (KOH), methylene blue, glucose (dextrose)
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 equilibrum
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(H
2
O)
6
2+
(aq)
+ 4 Cl
pink
-
(aq)
 CoCl
4
-2
(aq)
+ 6 H
2
O
(l)
blue/purple
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Equilibrium
Le Chatelier’s Principle Labs
Name_________________________
Per_____Date__________________
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 K c
expression for the above Reaction (I). Explain how changing the numerator or denominator changes the value of K c
for Reaction (I).
K c
=
Ammonia + phenolphthalein
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.
Reaction (II) NH
3 (aq)
+ H
2
O
(l)
 NH
4
+
(aq)
+ OH -
(aq)
Write the K c
for this reaction: K c
=
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 K c
value?
Is K c
for this reaction temperature dependent? Justify your answer.
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