Flashcards in Tutorial 4: Hydrolysis Of Aspirin Deck (13):
What rate of reaction is aspirin hydrolysis? Why?
The reaction is second order because it is dependent on the concentration and the solution pH
Why is the solution buffered?
So that the hydroxyl ion concentration remains constant. We can then rewrite the rate constant as -dA/dt = KappA
What will the degradation of aspirin buffered at pH7 ([OH] constant) then follow?
First order kinetics, where the rate of reaction, k is only dependent on the concentration of one reactant
What is the effect of pH on the hydrolysis of aspirin?
Aspirin hydrolyses in acid and base
Increased pH will increase hydrolysis
What is the effect of temperature on the hydrolysis of aspirin?
Increased temperature can increase the reaction rate
This in turn increases degradation
Describe the hydrolysis and stability of aspirin at different pH values
At pH 4 aspirin is most stable
Between pH 5-7: its decomposition is independent of pH
Above pH 10: the decomposition rate rapidly increases
What is shelf life?
The length of time required for the product potency to be reduced to some percentage of its original value
The time at which the product content is reducated to 90% of its original potency
Why is shelf life important?
It is desirable to determine the stability of the active ingredient in the drug so that a shelf life or expiration date may be assigned to the product
What are the components and their units of the Arrhenius equation?
Kapp: this is the apparent rate constant.
0 order (mol/L/min)
1st order: min-1
2nd order: L/mol/min
α = frequency constant
Ea= activation energy (kj/mol)
R = gas constant (1.987cal/mol/K or 8.314J/mol/K)
T = temperature (K)
What is the activation energy?
The minimum energy required for a chemical reaction to proceed
There must be sufficient number of molecules with energy equal or higher than Ea
What is the rearranged equation for activation energy?
lnKapp = lnα-Ea/RT
What is the rate constant?
The speed of the chemical reaction
Aka degradation rate of aspirin
Units = min-1