Diffusion Through Dialysis Tubing

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The effect of size on the effectiveness of diffusion

To use agar blocks infused with 0.1 Molar sodium hydroxide (NaOH) and phenolphthalein to investigate the relationship between shape and surface area: volume ratio on the effectiveness of diffusion.

That for a cube of agar, the time taken for complete colourisation due to diffusion of HCl is directly proportional to the cubes volume.

|A block of agar (10cm x 5cm x 3cm) with 0.1M NaOH and |1x 250mL beaker | |phenolphthalein to give a pink colour. |1x 100mL beaker | |Cutting board and knife |1M HCl | |Ruler with mm scale |1 x Timer |

1. From a prepared block of agar cut 5 cubes each at the following dimensions: -Side lengths of 10mm, 8mm, 6mm, 4mm, and 2mm.
2. Pour the 1M HCl solution into each of the beakers to a depth of 1.5 cm. 3. Place all pieces of agar into the solution at the same time and gently agitate while recording the time each takes to decolourise completely. 4. Record all raw data in the table you have prepared.


All organisms need to exchange substances such as food, waste, gases and heat with their surroundings. These substances must diffuse between the organism and the surroundings. The rate at which a substance can diffuse is given by Fick's law: |Rate of Diffusion α |surface area  x concentration difference | | |distance |

The rate of exchange of substances therefore depends on the organism's surface area that is in contact with the surroundings. The requirements for materials depends on...
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