Flashcards in Tutorial 4: Hydrolysis Of Aspirin Deck (13):

0

## What rate of reaction is aspirin hydrolysis? Why?

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

1

## Why is the solution buffered?

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

2

## 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

3

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

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Aspirin hydrolyses in acid and base

Increased pH will increase hydrolysis

4

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

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Increased temperature can increase the reaction rate

This in turn increases degradation

5

## Describe the hydrolysis and stability of aspirin at different pH values

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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

6

## What is shelf life?

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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

7

## 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

8

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

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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)

9

## 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

10

## What is the rearranged equation for activation energy?

### lnKapp = lnα-Ea/RT

11

## What is the rate constant?

###
The speed of the chemical reaction

Aka degradation rate of aspirin

Units = min-1

12