Lab 7.2: Le Chatelier s Principle

Transcription

1 Name Block Lab 7.: Le Chatelier s Principle Instructions: Introduction: In this on-line simulation we will be examining Le Chatelier s principle as it applies to equilibrium systems. Remember some reactions do not go to completion and are reversible primarily because of the relative instability of the products formed. If the product is relatively unstable the reaction process can sometimes be reversed to cause reforming of reactants. In this simulated lab we will look at various chemical systems and look at the effect of various factors on the reversibility of the chemical system.. Read the introduction and background information on the website before proceeding to the pre-lab questions.. Complete the pre-lab questions.. Complete the online lab. 4. Complete the post-lab questions. Prelab Questions:. Choose the statement that describes a solution that contains a system at equilibrium: a. one in which the color of the solution is changing slowly b. one in which the color is not changing. Explain your answer.. The following equilibrium is established when copper ions and bromide ions are placed in solution. heat + Cu(HO) Br - 6 HO + CuBr4 - The tube on the left contains only copper sulfate dissolved in solution. The tube on the right is the result of adding some potassium bromide solution. Given that the Cu(HO)6 + ion is blue and that the CuBr4 - ion is green, answer the questions below.

2 a. What happened to the concentration of each of the ions when the KBr was added? b. Explain why the solution changed color. c. Would the tube feel hot or cold when the KBr was added? Explain.. Consider the following equilibrium. Mg(OH) (s) Mg + + OH - The tube on the left contains Mg(OH)(s) and water. A chemical has been added to cause the change shown in the tube on the right. Suggest a possibility for what chemical could have been added. 4. Methanol has the formula CHOH and can be produced by the reaction of carbon monoxide with hydrogen gas. CO + H CH OH + heat In an attempt to maximize the yield of methanol (amount of methanol produced), a chemist would try to shift the equilibrium as far to the right as possible. Which of the following would accomplish this? Explain your answer. a. heating the mixture b. adding an excess of carbon monoxide c. removing the methanol as it is formed d. adding a substance that reacts with carbon monoxide This completes the pre-lab assignment. You may begin the experiment.

3 Online Lab Simulation Unless something is done to disturb a system at equilibrium it will remain at equilibrium. Any changes that disturb a system at equilibrium are called stresses. We are often able to predict the outcome of applying a stress to an equilibrium system using LeChatelier's Principle. It states that when an equilibrium system is disturbed, the system will shift in such a way as to relieve the applied stress. The three most common ways to stress a system at equilibrium are changing the concentration of one of the reactants or products, changing the temperature of the system, or changing the pressure on the system. As the last stress applies primarily to gaseous systems, we will concern ourselves with only the first two stresses. Instructions: In this experiment you will be shown a series of equilibrium systems and asked to apply certain "stresses" to the systems. The results of applying the stress will then be shown to you. For each system, record: (a) The effect the stress has on the concentration of each reactant and product in the reaction. Indicate if the concentration increases or decreases for each reactant and product. (b) Your observations This means a color change, a precipitate formed or some like statement. For example, "the red solution turned green". Do not use this part to state what chemical change occurred. For example, you should not say "more cobalt ion was formed". (c) What you think happened chemically State what chemical reaction occurred or species was formed that resulted in your observation. For example, "by adding chloride ion to the solution it shifted the equilibrium to the left which caused more CoCl 4- ion to be formed. Since this ion is blue, the solution became more blue." Setup for Each :. The picture of the original reaction mixture (in the middle) before any stress is applied.. The stresses you can apply: means heating the solution means cooling the solution means adding a chemical (in this case KCl). When you apply the stress by clicking on the image, another picture will come up. On the left of the picture will be the original solution. On the right will be the solution after the stress has been applied. 4. Any special comments you will need.

4 I. Cobalt

5 II. Ammonium :

6 III. Iron Thiocyanate : 4 4

7 IV. Chromate : V. Nitrogen Dioxide :

8 VI. Copper Sulfate :

9 Post Lab Questions. Predict what would happen if the ammonium system described in the experiment was heated.. Consider the following equilibrium. Cu NH Cu(NH)4 + The copper ion in solution is light blue. The Cu(NH)4 + ion is a deep blue. The tube on the left contains only copper ions. Identify what chemical was added to produce the results shown in the center tube. Identify what chemical may have been added to the center tube to produce the results shown in the right tube.. The barium ion is toxic to humans. However, barium sulfate is commonly used as an image enhancer for gastrointestinal x-rays. What does this imply about the position of the equilibrium shown below. BaSO4 Ba + + SO4-4. Hemoglobin (Hb) and oxygen gas form a complex (HbO) that carries oxygen throughout the human body. Unfortunately, carbon monoxide also binds to hemoglobin so that an equilibrium is established. Carbon monoxide poisoning occurs when the concentration of HbO in the blood is reduced. HbO + CO HbCO + O The first aid for a person suffering from carbon monoxide poisoning is to () remove them to an area of fresh air, and () administer oxygen. Using the principles of equilibrium, explain how each of these helps to restore the HbO concentration. Complete the QUIZ online...include your score. / 0