Le Châtelier\'s Principle 110 4. Le Chatelier\'s Principle can be used to predic

Question

Le Châtelier's Principle

110 4. Le Chatelier's Principle can be used to predict the effect on the concentra tion of one component in an equilibrium when the concentration of another com- ponent Is changed. In answering these questions do not say "shifts right" or "shifts left"; rather say "toward" or "away from" something. a) Use Le Châtelier's Principle to predict the effect on [FeNCS] of usinga larger initial concentration of SCN. (View this as an equilibrium which is then disturbed by adding more SCN.) State how you arrived at your prediction. b) Does the change in absorbance between Tubes 2 and 3 confirm what you have pre- dicted using Le Châtelier's Principle? Discuss how it agrees/disagrees. Does your prediction agree for Tubes 4 and 5 (--/N)? c) Use Le Chateller's Principle to predict the effect on [FeNCs*1 of using a smaller initial concentration of Fe. State how you arrived at your predic tion. (Viex this as an equilibrium from which you remove some Fe) d) Does the change in absorbance between Tubes 1 and 2 confirm what you have pre- dicted using Le Châteller's Principle? Discuss how it agrees/disagrees. Does your prediction agree for Tubes 3 and 4 Y/N)

Explanation / Answer

LeChatellier's principle

Fe3+ + SCN- <==> FeNCS^2+

a) A large concentration of SCN- would shift the equilibrium towards right handside, that is more FeNCS^2+ would be formed until all of SCN- is consumed and equilibrium is re-established.

b) Yes, the absorbance of test tube 2 and 3 confirm the change seen in a), the color of solution becomes darker in excess of SCN-.

c) With smaller initial concentration of Fe3+, [FeNCS]^2+ concentration would reduce, more of complex would dissolve to form free Fe3+in solution. The reaction shifts to the left, more reactants are formed until equilibrium is reestablished. the color of solution becomes lighter.

d) Test tubes 1 ands 2, confirm this change by absorbance, the color becomes lighter over time.

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