This experiment will allow you to find how surface area/volume ratio affects the rate of diffusion.

Equipment

Hydrochloric Acid solution (1 molar)

Beaker

Stopclock

Agar cubes of different sizes (three each with sides of 0.5 to 3 cm in 0.5cm intervals) made using alkali and Phenolphthalein indicator

Tweezers

White paper

Deionised water

Goggles

Method

Using the tweezers add one of the smallest cubes to the beaker. Place the beaker on the white paper so as to me able to monitor the colour change easily.

Pour the enough acid into the beaker to just cover the cube and start the stopclock. Stop the stopclock when the cube has become clear. Record the time taken.

Empty the beaker and rinse out using the deionised water.

Repeat with the remaining two 0.5cm side cubes.

Repeat the entire process using the remaining cubes.

Calculate the surface area and volume of each cube. Divide the surface area by the volume and plot a graph of this value against the time taken for the diffusion to complete.

Safety

Goggles must be worn when working with acids. Tweezers should be used when moving the cubes as the indicator used acts as a laxative. Care should also be taken to wash hands after completing the experiment.