Does the size affect the rate of diffusion.

Hypothesis: the rate of diffusion is not affected.

Tols: 3 beakers, a scalpel, a sufficient amount of Sodium Hydroxide (more or less 150ml), a block of agar, a lab "spoon", a watch, paper towels, a centimeter ruler, and the top of a cover slip box.

Procedure:

We pressed the cover slip box against the block of agar, and cut all sides of the cover slip box so as to keep the agar contained inside the box, stopping us from using extra agar. The agar was then softly taken out of the cover slip box. This was repeated until we had several equal sized cubes. The dimensions of the agar cubes were not equal so we had to trim them as well, using the scalpel and the centimeter ruler. We wanted three sides, 2.0cm, 1.5cm, and 1cm cubes. The blocks were then submerged in to NaOH for five minutes, in such a way that the agar block was covered completely. After the five minutes the blocks were taken out, dried, and cut. With a ruler then the area and volume that was left uncolored (unaffected by the NaOH). The total volume that was not affected was subtracted from the total volume to find out the volume that was diffused. The percentage was then found of the agar that was not affected. This was then repeated again to obtain an average.

Data collection:

st set of data

Size of agar

Volume of agar

Area non-diffused

Volume non-diffused

Volume diffused

Percentage diffused

2cm

8

.4

2.7

5.3

66%

.5 cm

3.4

.9

.7

2.7

79%

cm

.4

.06

.94

94%

2nd set of collection

Size of agar

Volume of agar

Area non-diffused

Volume non-diffused

Volume diffused

Percentage diffused

2cm

8

.5

3.4

4.6

49%

.5cm

3.4

2.4

62%

cm

.6

.2

.8

80%

Average:

Size of agar

Volume of agar

Area non-diffused

Volume non diffused

Volume diffused

Percentage diffused

2cm

8

.5

3.4

4.6

57.5%

.5

3.4

2.4

70.50%

cm

.5

.13

.87

87%

Variables that could have had affected the rate of diffusion:

. concentration of sodium hydroxide

2. the texture of agar

3. temperature, the hotter the agar the more readily can the reaction take place between agar and NaOH.

The first time we conducted the experiment, the agar was harder than it was the second time. The agar was much softer the second time, as if we poked the agar the agar would give way to our finger. This could be the reason for which our results were different than the first time we conducted the experiment.

From the results we see that the smaller the agar block, the greater the diffusion. This is because of surface area to volume ratio. Thus the smaller the cube the faster the diffusion.

What we notice thus is that the rate of diffusion doesn't change, as long as the variables stay the same. The reason for which the smaller cube had a greater diffusion than the other cubes, is because of its surface area. Although the volume changed only superficially the surface area changed dramatically. This explains the reason for which the cells are microscopic. They need to be so as to be able to get their nutrients in them fast enough, had they been any bigger the diffusion wouldn't be fast enough thus killing the cell.

This experiment was done in a rather efficient way as it was finished in a short amount of time. The only problem is that we used 2 different blocks of agar. Next time it would be much best to use the same block to experiment with. To increase accuracy it would be best not to use a scalpel to cut straight edges. A ready made tool that would do the job automatically and more precisely would be more time efficient and accurate.

What would be more interesting would be to use different substances to experiment with other than agar, such as play-do, and jell-o. this way we could see which substance is easier to diffuse things in to, and out of. That way we could see which artificial substances are better diffusing, foods or toys.