Stress Management Lechatelier S Principle Lab

Stress Management – LeChatelier’s Principle Lab

Name: ______Date: ______

Problem: How can Le Chatelier’s principle be used to predict the direction in which a system at equilibrium will shift when conditions are altered?

Materials: CuCl2 (s), 0.1 M AgNO3 (aq), NaCl(s), water, test tube rack, 5 test tubes, 100 ml beaker, balance, hot water bath

Prelab: The equilibrium system that we will be studying is as follows:

+2 -1 CuCl2(aq) ⇄ Cu (aq) + 2 Cl (aq) + heat (green) (blue) (colorless)

1. Write out the balanced reaction between AgNO3 (aq) and CuCl2 (aq) and identify the precipitate formed.

a) Does precipitation mean that the concentration of the compound that is the solid increases or decreases in the aqueous solution?

3. For each change listed, predict the equilibrium shift and the resulting color, using the reactions above and your knowledge of Le Chatelier’s principle:

Direction Stress of Shift Predicted Color ( ; ; or no change) Raise temperature Lower temperature

+ - Add Ag NO3 Add Na+Cl-

4. Calculate how many grams of CuCl2 are needed to make 30 ml of a 0.5 M solution: Procedure:

1. Obtain the number of grams of CuCl2 that you calculated in the prelab and add them to your beaker. 2. Add enough distilled water to the beaker to make 30 ml of solution and swirl to

completely dissolve the CuCl2.

3. Put your 5 test tubes in the test tube holder and evenly divide your CuCl2 solution among them. 4. Fill in the data table below with the observed color of the solution after each stress is added. The control group is the tube which is not stressed and the color of all stressed tubes can be compared to it.

5. Stress each test tube by doing the following: a. Place one test tube in a hot water bath for at least 5 min to raise the temp. b. Hold one test tube under running cold water from the sink for at least 1 min to lower the temp.

c. Add 5 drops of AgNO3 solution to one test tube. d. Add a scoop of NaCl to the last test tube.

Data: Stress Resulting Color Control Raise temperature Lower temperature

+ - Add Ag NO3 Add Na+Cl-

Conclusion Questions:

1. What affect did heating the test tube have on the concentration of Cu+2? Explain how you know this by using Le Chatelier’s Principle.

2. Using the reaction that you wrote in the prelab, explain what happened when you

added AgNO3 to the test tube and why that caused the equilibrium to shift in the direction that it did. 3. When you added NaCl to the solution, which ion was stressing the equilibrium, Na+ or - Cl ? How did this affect the concentration of CuCl2?

4. Here’s a biological example of an application of Le Chatelier’s principle:

Hemoglobin (Hb) reacts with oxygen to form HbO2, a substance that transfers oxygen to the tissues in the body. This is necessary for life as oxygen alone cannot

be absorbed by tissues. Carbon monoxide (CO) also reacts with HbO2 by the process below.

HbO2(aq) + 4CO(aq) < -- > Hb(CO)4(aq) + O2(aq)

a) Use LeChatelier’s Principle to explain why inhaling CO can cause death, knowing

that oxygen must be in the form HbO2(aq) in order to be used in the body.

b) Use LeChatelier’s Principle applied to this equation to suggest a treatment for a victim of CO poisoning. Explain how your treatment affects the equilibrium above.