The alkaline hydrolysis of ethyl ethanoate follows rate = k[ester][OH-]. When the reaction is run with a very large excess of NaOH, the observed kinetic order is

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The alkaline hydrolysis of ethyl ethanoate follows rate $= k [ester] [OH X^{-}]$ . When the reaction is run with a very large excess of NaOH, the observed kinetic order is

With

[OH X^{-}]

essentially constant, rate

= k^{'} [ester]

with

k^{'} = k [OH X^{-}]

. The reaction is overall second order but appears first order in the ester, i.e. pseudo-first order.