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    Le Chateliers Principle

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    I already know what Le Chatliers Principle is, but I need help describing what is going on in specific in the following reactions. For example, how is the chemical equation changing to minimize change.

    1. Bromine water is initially yellow/brown but changes to yellow when sodium hydroxide is added. Then when sulfuric acid is added the solution turns yellow/brown again.
    What is happening? Note: Br2(aq) + H2O(l) <----> HOBr2(aq) + Br2 -(aq) + H+

    2. Potassium chromate is initially yellow. When sulfuric acid is added the solution turns orange. Then when sodium hydroxide is added the solution turned back yellow.
    What is happening? Note: CrO4 2-(aq) + 2H+(aq) <-----> Cr2O7 2-(aq) + H2O(aq)

    3. Ethyl acetoacetate and water are clear initially, then when iron(III) chloride is added the solution turned deep purple. Then when bromine water was added the solution turned clear. Over time the deep purple color reappeared in the solution.
    What is happening? Note: Ethyl acetate exists as an equilibrium mixture of two forms(called tautomers) -when iron(III) chloride is added to ethylaccetoacetate the solution becomes coloured because of a reaction between the enol form and the iron(III) chloride. The enol form of ethylacetoacetate also reacts with bromine water.

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    Solution Preview

    For questions 1 and 2 you need to know that sodium hydroxide (NaOH) is a strong base (produced OH- ions) while sulfuric acid is a strong acid (produces H+ ions).
    Q1) When NaOH is added, the OH- derived from this base reacts with the H+ that already exist in the equation to form water (H2O). Therefore, all of a sudden it is as if you are adding more water to the reaction and according to Le Chatelier's principle the reaction is shifted to the right, which results in production of more aqueous bromine and hence the yellow color. On the other hand when a strong acid is added it is as if you are ...

    Solution Summary

    The solution discusses Le Chateliers Principle.