Answer Happy

(b) Carrying out the hydrolysis with different concentrations of the buffer components gives the following kinetic data (where kobs is the observed pseudo-first-order rate constant for hydrolysis). /mol dm- [BH] /mol dm3 kobs / s-1 1 3.5 x 10-2 1.0 x 10-2 1.50 x 10-3 2 7.0 x 10-2 2.0 x 10-2 2.30 x 10-3 3 7.0 x 10-2 4.0 x 10-2 4.56 x 10-3 4 14.0 x 10-2 4.0 x 10-2 3.82 x 10-3 X (i) ( [2] [4] (ii) (iii) Given the pKa of BHis 6.40, calculate the pH of the buffer in table entry 1. I Explain why the data in the table suggest general acid catalysis. Use a graphical method to determine the values of key, the rate constant for catalysis by BH*, and kh, the rate constant for catalysis by H3O*. Include the graph in your answer. If the analysis is repeated using D20 in place of H2O, KBH is found to be 3.75 x 10-2 mol-1 dms-1. Determine the solvent kinetic isotope effect and explain the significance of the value obtained. [6] (iv) [3]