 Solution

ID: past-exam-of-the-chemistry-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2021/paper-1/5/a/i/solution

For the stated single elementary step and constant reaction volume,

v = - \frac{d [ MeX ]}{d t} = - \frac{d [ O H ^{-} ]}{d t} = \frac{d [ MeOH ]}{d t} = \frac{d [ X ^{-} ]}{d t} = k [MeX] [O H^{-}] .

The equal magnitudes follow from the unit stoichiometric coefficients. In the buffered case this hydroxide consumption is balanced by buffer chemistry; the measured total hydroxide concentration can then remain constant.

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