Relationship Between Shape and Diffusion Rate Essay
Sorry, but copying text is forbidden on this website!
To see whether there is a relationship between the surface area and the diffusion rate
I predict that the smaller blocks of agar will turn clear, or diffuse first, as it has a smaller surface area. This is because there is less surface area and volume for the sulphuric acid to diffuse into.
* Three sizes of agar, 20x20x20mm, 20x20x10mm, 20x20x5mm
* 240ml of sulphuric acid [80ml per beaker]
* 3 100ml beakers
* Tile used for placing the agar
* Tissue to wipe off the sulphuric acid off the agar
* 3 scalpels
* Ruler, measurable in mm
* Stop clock
1. First, cut three pieces of sulphuric acid in the following sizes 20x20x20mm, 20x20x10mm, 20x20x5mm, as accurately as possible
2. Next, fill the three beakers with 80ml of sulphuric acid each
3. Then, prepare the stop clock, and make sure it is has been reset
4. After, place the three blocks of agar into the sulphuric all at the same time, as well as starting the stop clock once the agar is in the sulphuric acid.
5. Carefully stir the three beakers using the scalpels.
6. Watch until one of the blocks have gone completely clear.
7. Once one of the blocks have gone completely clear, stop the stop clock and take out the three blocks of agar and place on the tissue, and wipe off the excess sulphuric acid from the blocks of agar to prevent further diffusion with the two other blocks which have not been fully diffused to fully diffuse
8. Cut the blocks in diagonal, through the middle and using a ruler, measure how much of it has turned clear on each side.
9. Record the data for time taken, and the depth of the clear part on the table.
Predicted order of clearing
Actual order of clearing
Time taken for clearing
Depth of clear part on block/mm
Surface are to volume ratio
My prediction as to which block will go clear first was correct, being the smaller block, as its surface area to volume ratio was the greatest out of all three, even though there was not much difference between the three values. This is because the third block has a greater surface area for the sulphuric acid to diffuse into the agar, causing the diffusion rate to be greater. The blocks have become ‘clear’ through diffusion caused by neutralization between the sulphuric acid and the agar, which is an alkaline.
Quite a few things did not go as planned in this evaluation, but I have come up with ideas on how to improve them if we do an experiment like this again. Firstly, the jelly size may not be accurate from cutting it, and when it has been stirred, bits of it may have chipped off causing a change in its surface area. Next time, to avoid this, we could measure the block of agar more accurately when cutting it, and also be more careful when stirring the agar and stir softer so that no bits may get chipped off.
Not only that, but the time we place the three blocks of agar into the sulphuric acid may be different, as well as the time we started the stop clock. Next time, we may possibly find a different method of putting in and taking out the agar so that it remains a fair test, and so that there are less mistakes in the test, which may be reduced by having one person per block of agar and beaker, as well as another person for the stop clock and placing it in and taking it out all at the same time as well as starting and stopping the stop clock.
Another complication may have come from the amount of sulphuric acid in each beaker, which may not have been equal. This problem may be reduced by measuring the sulphuric more carefully, maybe with a measuring cylinder before then placing it into the beaker, instead of measuring it into the beaker straight away.
Our measurements of the depth of the clear layer of the blocks of agar jelly may have been incorrect as well, and to prevent this, we could possibly use a microscope next time and use a graticule to measure the depth that the jelly has diffused to obtain a more accurate result.
The last problem I noticed while doing the experiment was when we were blotting the sulphuric acid off the agar. I found that there may have been some sulphuric acid left on the agar after we have blotted it, which may have caused further diffusion and adjusting our result. This is caused from not blotting off enough sulphuric acid off the agar. Next time, we could carefully blot all the sulphuric acid, and use one piece of tissue for each block of agar so that there is no sulphuric acid on the tissue before blotting each block of agar.