Agar blocks

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                                                        Experiment showing rate of diffusion in agar blocks

Factors: Size of agar block

               Concentration of hydrochloric acid (Hcl)

Hypothesis: I predict that the bigger the Agar blocks the more time it will take for it to completely diffuse due to the fact that the surface area to volume ratio decreases with size. As for the concentration of the acid I feel that the greater the amount of moles in the acid the quicker the rate of diffusion as the phenolphthalein indicator will diffuse from an area of high concentration to an area of low concentration.

Materials and equipment:

Beaker

Measuring cylinder

Knife

Agar blocks containing phenolphthalein indicator

Ruler

Hydrochloric acid

Tweezers

Stop watch

Effect of size on rate of diffusion

Procedure #1

  1. Cut a pair of agar blocks with a knife to a size 0.5×0.5×0.5 repeat the same for sizes’ of 1.0×1.0×1.0 and 1.5×1.5×1.5
  2. Using a measuring cylinder measure 40ml of hydrochloric acid (1mol)
  3. Using tweezers put all of the cubes in a beaker containing 40ml (1 mol) of hydrochloric acid
  4. Measure length of time for agar blocks to go from pink to white using stop watch.
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Effect of concentration on rate of diffusion

Procedure #2

  1. Six agar blocks are cut into size 1.5cm³ using knife
  2. 40ml cube of hydrochloric acid (0.75, 0.5 and 0.25 moles each separate) are put into a beaker, different beaker for each concentration.
  3. 2 of the 6 agar blocks are put into the beaker containing 0.75 moles of Hcl. 2 blocks are put into beaker containing 0.5 and 2 blocks in beaker containing 0.25 moles of Hcl.
  4. Time taken for agar blocks to go from pink to white is recorded using stopwatch.

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*** A reasonably well conducted experiment but a lack of specific detail and scientific terms in the method together with incorrect graph plotting are major shortfalls.