AP Chemistry 5.11: Catalysis

Practice AP Chemistry questions on explaining how catalysts alter mechanisms and activation energy while remaining regenerated with constant net concentration.

[Maximum number: 1]

Answer the following questions about the glycolate ion, $\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{3}{ }^{-}$ , which acts as a base in

aqueous solution. A Lewis diagram for the ion is provided.

Figure for Question 5.11.A—Explain the relationship between the effect of a catalyst on a reaction and changes in the reaction mechanism question 1 — AP Chemistry

Glycolic acid can be produced from the hydrolysis of methyl glycolate, $\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}$ . A proposed

mechanism for the reaction is given.

\begin{aligned} & \text { Step 1: } \mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}+\mathrm{H}_{3} \mathrm{O}^{+} \rightleftarrows \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}_{3}{ }^{+}+\mathrm{CH}_{3} \mathrm{OH} \\ & \text { Step 2: } \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}_{3}{ }^{+}+\mathrm{H}_{2} \mathrm{O} \rightleftarrows \mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{3}+\mathrm{H}_{3} \mathrm{O}^{+} \\ & \text {Overall: } \mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}+\mathrm{H}_{2} \mathrm{O} \rightleftarrows \mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{3}+\mathrm{CH}_{3} \mathrm{OH} \end{aligned}

A student claims that $\mathrm{H}_{3} \mathrm{O}^{+}$ is a catalyst for the reaction. Do you agree or disagree? Justify

your answer based on the mechanism given.

C For the correct answer and a valid justification:

Point 04

Agree. $\mathrm{H}_{3} \mathrm{O}^{+}$ is consumed in step 1 and regenerated in step 2, which is consistent with the

behavior of a catalyst.

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5.11.A—Explain the relationship between the effect of a catalyst on a reaction and changes in the reaction mechanism question 1