The hydrolysis of bromoethane in basic solution produces ethanol by the overall…

CHEMISTRY · Multi-part · AP · Chemistry · Kinetics · Kinetics

Problem

The hydrolysis of bromoethane in basic solution produces ethanol by the overall stoichiometry C2H5Br+OH−→C2H5OH+Br−\mathrm{C_2H_5Br} + \mathrm{OH}^{-} \rightarrow \mathrm{C_2H_5OH} + \mathrm{Br}^{-} Experimental kinetics at 298 K298\,\text{K} give the rate law rate=k[C2H5Br][OH−]0.5\text{rate} = k[\mathrm{C_2H_5Br}][\mathrm{OH}^{-}]^{0.5} Two proposed mechanisms are under consideration: Mechanism A 1. C2H5Br⇌C2H5++Br−\mathrm{C_2H_5Br} \rightleftharpoons \mathrm{C_2H_5^+} + \mathrm{Br}^{-} (fast equilibrium) 2. C2H5++OH−→C2H5OH\mathrm{C_2H_5^+} + \mathrm{OH}^{-} \rightarrow \mathrm{C_2H_5OH} (slow) Mechanism B (1) Part 1: For each mechanism, write the rate law that would be expected if the step identified as slow controls the overall rate. Clearly state any approximations or substitutions made. (2) Part 2: Identify which mechanism, if any, is consistent with the experimentally determined rate law, and justify your choice with quantitative or qualitative reasoning. (3) Part 3: Explain the chemical meaning of the fractional order (0.50.5) in OH−\mathrm{OH}^{-} concentration, and discuss one experimental observation that could confirm the presence of such a non-integer order.

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