[Janhaa]

A drug, AS, is converted to an inactive form, IF:
Given reaction:
 AS → IF
The stability of AS depends on pH. The initial rates, v0, have been measured at 25 °C.
Where [AS]o = 10.0 mM.

The rates were:
pH |4 | 5| 6 | 7 | 8 | 9 | 10 |
v0 (mM/s)| 0.02| 0.021| 0.025| 0.070| 0.52| 5.0| 50|

These data suggests that the observed pseudo first-order rate constant, k(obs), is given by:

k(obs) = k(0) + k(1)*[OH^-] and

v = rate = k(obs)*[AS]
finally:

determine k(0) and k(1)
*****************
Is a pseudo first-order meaning a second order kinetics?

Can anyone give me a hand

[mjc123]

Pseudo first order means the reaction is first order in [AS] when conditions are chosen so that it is effectively zero-order in any other reagent. This can be done by having the other reagents in large excess, so that their concentrations don't change significantly during the reaction. In this case, since at these pH values [OH^-] is not in excess over [AS], the solution must be buffered, so that the pH doesn't change.