the larger the blocks , the slower the rate of diffusion as
the larger the surface area the faster the rate
method step 1
Coloured agar is made up and cut into cubes of the required dimensions (eg. 0.5cm x 0.5cm x 0.5cm, 1cm x 1cm x 1cm and 2cm x 2cm x 2cm)
what is purple agar made of
with very dilute sodium hydroxide solution and Universal Indicator
Alternatively, the agar can be made up with Universal Indicator only
step 2
the cubes are then placed into boiling tubes containing a diffusion solution (such as dilute hydrochloric acid)
cv for solution
same volume of diffusion concentration (dilute hydrochloric acid )
The acid should have higher molarity than the sodium hydroxide so that its diffusion can be monitored by a change in colour of the indicator in the agar blocks
measurements taken as
The time taken for the acid to completely change the colour of the indicator in the agar blocks
you can also measure
The distance travelled into the block by the acid (shown by the change in colour of the indicator) in a given time (eg. 5 minutes)
