52nd IChO 2020 International Chemistry Olympiad, Istanbul, TURKEY

52nd International Chemistry Olympiad, Istanbul, TURKEY

Preparatory problems: PRACTICAL

Problem P7. Determination of Rate Constants for n-Butyl Acetate Hydrolysis Hydrolysis, in other words splitting with water, is one of the most important reaction types that an ester can undergo. The hydrolysis of ester can be catalyzed either by acids or by bases and when the catalyst is a base, the reaction yields a carboxylate salt and an alcohol.

In this experiment, you are asked to determine rate constants of the alkaline hydrolysis of nbutyl acetate using sodium hydroxide, which is a typical second-order reaction.

The rate of the reaction can be calculated by the following equation: Reaction rate = k[CH3COOC4H9][OH − ] Then 1 1 – = k × 𝑡, [A] [A]0

where [A] is the concentration of reactant at time t ([A]= [B]), [A]0 is the initial concentration and k is the second-order constant, which has dimension of concentration–1 time–1 (L mol–1 s– 1). In this case, a characteristic plot that will produce a linear function is 1/ [A] vs. time t, with a slope of k.

Chemicals Substance

Name n-Butyl acetate

State Aqueous solution

GHS Hazard Statement H226, H336, P210

NaOH

Sodium hydroxide

Aqueous solution

HCl

Hydrochloric acid

Aqueous solution

H290, H314, P280, P301 + P330 + P331, P303 + P361 + P353, P305 + P351 + P338 + P310 H290, H314, H335, P260, P280, P303 + P361 + P353, P304 + P340 + P310, P305 + P351 + P338 + P310

209