Consider the following reaction involving bromophenol blue (BPB) and OH: 

HBPB(aq) + OH^– (aq) → BPB^–(aq) H₂O(l)

The concentration of HBPB can be monitored by following the absorption of this species and using the

Beer–Lambert Law. In this law, absorption, A, and concentration are linearly related.

a. Express the reaction rate in terms of the change in absorbance as a function of time.

b. Let A0 be the absorbance due to BPB at the beginning of the reaction. Assuming that the reaction is first order with respect to both reactants, how is the absorbance of BPB expected to change with time?

c. Given your answer to part (b), what plot would you construct to determine the rate constant for the reaction?