Reaction Rate Constant Determination by Titration

In a reaction, if one of the reactant is the solvent, then this reactant is present in large excess, such as for instance in a hydrolysis reaction.So its concentration can be considered as constant. Thus a bimolecular hydrolysis follows a pseudo-first order kinetics, i.e.  the reaction rate is mainly determined by the concentration of the reactant times the rate constant.
One such example is represented by the hydrolysis of acetic acid anhydride in which the reaction rate follows a pseudo first-order kinetics.

Reaction:

Hydrolysis         (CH₃CO)₂O + H₂O → 2 CH₃COOH

To monitor the reaction as a function of time, acetic acid is neutralized with sodium hydroxide to a predefined pH value during time, i.e. by using a pH-Stat titration:

Neutralization     NaOH + CH₃COOH → CH₃COONa + H₂O

In this application, the system under study is the hydrolysis reaction of acetic acid anhydride.
The value for the rate constant is obtained from the slope of the line obtained by plotting the concentration of unreacted acetic anhydride  as a function of time.

Also it is known that change in the temperature affects the rate constant, therefore temperature variations studies have also been carried out  to study the temperature dependence  of the reaction rate constant.