Introduction to Le Chatelier's Principle

AP Chemistry· difficulty 1/5

A student adds the following stresses one at a time to separate samples of an equilibrium mixture of [Co(H2O)6]^2+ (pink) <-> [CoCl4]^2- (blue) + 6 H2O (delta H > 0 forward) and records color change: Trial A: heat the solution -> turns blue Trial B: add concentrated HCl -> turns blue Trial C: add AgNO3 -> turns pink Trial D: add water -> turns pink

Stress Observation A: heat turns blue B: add HCl turns blue C: add AgNO3 turns pink D: add water turns pink

Which observation is best explained by Le Chatelier's principle removing Cl-?

  • A

    Trial A

  • B

    Trial B

  • C

    Trial C

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  • D

    Trial D

Explanation

AgNO3 precipitates AgCl, removing Cl-. The equilibrium shifts back toward [Co(H2O)6]^2+ (pink).

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