for part 1 of this experiment, explain what you will actually observe (see) in the laboratory that will let you know to which side the equilibrium has shifted when it is stressed.
Added by Jennifer M.
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This may involve observing the concentrations of reactants and products, as well as any physical changes such as color, temperature, or gas production. Show more…
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- Describe how the equilibrium was established. - Then explain what occurred when each stress was applied in terms of Le Chatelier's principle. To do so, you must 1. identify the specific stress, 2. use Le Chatelier Principle to predict a "shift left" or "shift right" 3. use your experimental observations to support each prediction. - Balanced equations must be presented. The questions below are meant to guide your discussion of each part: Part A: Acetic Acid/Acetate Equilibrium a) Explain the significance of the first pH measurement. b) Explain what happened when the sodium acetate was added. Part B: Chromate/Dichromate Equilibrium a) Identify which ion is orange and which ion is yellow. b) Explain why the original solution has the color that it does. c) Explain what happened when acid and base were added. Part C: Bismuth Trichloride Equilibrium a) Explain what happened when the solid BiCl3 was added to water. b) Explain what happened when the acid was added. c) Repeat part b above for water. Be careful! This is tricky. Part D: Cobalt/Cobalt Chloride Equilibrium a) What color is the [Co(H2O)6]2+ ion? What color is the [CoCl4]2- ion? b) Explain the color change that occurs when the HCl is added. c) Explain the color changes that occurred when heat was added or removed. d) Is the reaction exothermic or endothermic? Explain. Part E: Iron/Iron Thiocyanate Equilibrium a) What color is the Fe3+ ion? What color is the SCN- ion? What color is the [Fe(SCN)]2+ ion? b) Explain the color change that occurred when KSCN and Fe(NO3)3 were mixed. c) Explain the color changes that occurred when heat was added. d) Is the reaction exothermic or endothermic? Explain. e) Explain the color changes that occurred when excess reactants were added. f) What precipitate formed when AgNO3 was added? Explain the equilibrium shift that occurred when AgNO3 was added. You might find it helpful to consult a solubility table. Part F: Bicarbonate/Carbon Dioxide Equilibrium a) What product was removed by aspiration? b) Explain the indicator color change.
Sri K.
Prelab Assignment: Chemical Equilibrium and Le Chatelier's Principle 1. Consider the reversible reaction: A + B ⇌ C + D a. What happens to the forward and reverse reaction rates when equilibrium is achieved? b. What happens to the reactant (A and B) and product (C and D) concentrations when equilibrium is achieved? 2. Le Chatelier's Principle states that if a stress is applied to a reversible reaction at equilibrium, the reaction will undergo a shift in order to re-establish its equilibrium. Consider the following exothermic reversible reaction at equilibrium: 2 A ⇌ B + C In which direction (left or right) would the following stresses cause the system to shift? a. decrease the concentration of A b. increase the concentration of B c. lower the temperature 3. In this lab you will explore the effect of Le Chatelier's Principle on several chemical systems at equilibrium. These are supplied on page 2 of the Theory Section. Consider the third system you will study: the Aqueous Ammonia Solution. a. Write the balanced equation for this reversible reaction. b. Suppose you added some excess ammonium ions to this system at equilibrium. -- In which direction would a shift occur? -- What color change might you expect to observe? 4. List all the equipment you will use in this lab.
Adi S.
Consider the reversible reaction: A + B ⇌ C + D What happens to the forward and reverse reaction rates when equilibrium is achieved? What happens to the reactant (A and B) and product (C and D) concentrations when equilibrium is achieved? LeCh"atelier’s Principle states that if a stress is applied to a reversible reaction at equilibrium, the reaction will undergo a shift in order to re-establish its equilibrium. Consider the following exothermic reversible reaction at equilibrium: 2 A ⇌ B + C In which direction (left or right) would the following stresses cause the system to shift? The concentration of A is decreased. The concentration of B is increased. The temperature of the system is lowered. In this lab you will explore the effect of LeCh"atelier's Principle on two different systems at equilibrium. Part I: Cobalt Complex Co(H2O)6^2+(aq) + 4 Cl— (aq) ⇌ CoCl4^2—(aq) + 6 H2O (l) pink blue Part II: Aqueous Ammonia (phenolphthalein indicator) NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH—(aq) Suppose you added excess ammonium ion to the aqueous ammonia equilibrium above. In which direction would a shift occur? What color change might you expect to observe?
Nicole S.
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