Tutorial 4: Hydrolysis Of Aspirin

Question 0

Why is the solution buffered?

Answer 0

So that the hydroxyl ion concentration remains constant. We can then rewrite the rate constant as -dA/dt = KappA

Question 1

What rate of reaction is aspirin hydrolysis? Why?

Answer 1

The reaction is second order because it is dependent on the concentration and the solution pH

Question 2

What will the degradation of aspirin buffered at pH7 ([OH] constant) then follow?

Answer 2

First order kinetics, where the rate of reaction, k is only dependent on the concentration of one reactant

Question 3

What is the effect of pH on the hydrolysis of aspirin?

Answer 3

Aspirin hydrolyses in acid and base

Increased pH will increase hydrolysis

Question 4

What is the effect of temperature on the hydrolysis of aspirin?

Answer 4

Increased temperature can increase the reaction rate

This in turn increases degradation

Question 5

Describe the hydrolysis and stability of aspirin at different pH values

Answer 5

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

Question 6

What is shelf life?

Answer 6

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

Question 7

Why is shelf life important?

Answer 7

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

Question 8

What are the components and their units of the Arrhenius equation?

Answer 8

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)

Question 9

What is the activation energy?

Answer 9

The minimum energy required for a chemical reaction to proceed

There must be sufficient number of molecules with energy equal or higher than Ea

Question 10

What is the rearranged equation for activation energy?

Answer 10

lnKapp = lnα-Ea/RT

Question 11

What is the rate constant?

Answer 11

The speed of the chemical reaction

Aka degradation rate of aspirin

Units = min-1

Question 12

In the y=mx+c type equation what is the rate constant?

Answer 12

The m value i.e, the gradient