Investigate the rate of diffusion of Hydrochloric Acid into Gelatine.

Tom Chapman

Biology Coursework

PLANNING

Introduction

In this experiment I am going to investigate the rate of diffusion of Hydrochloric Acid into Gelatine. To do this I will use the same concentration and amount acid with the gelatine being cut into different sizes. The rate of diffusion is dependant on the surface/volume ratio to how quick the acid is able to diffuse throughout the whole of the gelatine.

Equipment

Hydrochloric Acid
Gelatine
Tile
Test tube
Rubber Bung
Scalpel
Ruler
Stop Clock
Goggles
Measuring Cylinder

Experiment

In the experiment I will first of all cut up the pieces of gelatine into the correct sizes using the scalpel, tile and ruler. This must be done accurately otherwise this could affect the end results. I will then measure out 30ml of Hydrochloric Acid using the measuring cylinder and pour it into the test tube. I will then put in the gelatine shapes. I will then quickly put the bung in the stop and start the stop clock. I will hold the test tube at a horizontal position so that the acid in covering all of the surfaces of the cubes and so all the cubes are separate being easily visible. I will write down the time when each cube has been fully diffused, I can tell this because it is when they turn from an orange colour to red. When the gelatine has been fully diffused there will no orange left, just red. Through out this experiment I will wear safety goggles to protect my eyes from the acid. The sizes of the shapes of gelatine will be:

10mm x 10mm x 10mm
10mm x 10mm x 5mm
10mm x 5mm x 5mm
5mm x 5mm x 5mm

I have chosen these sizes carefully so that I will be able to compare and link the results together, hopefully finding a pattern.

Fair test

I will use the same quantity and concentration of Hydrochloric Acid (30ml) for all the experiments. The same type of gelatine will be used which will be cut to the exact same sizes. The temperature at which the experiments will be done will be the same, room temperature. The only variable will be the size of the gelatine cubes. I have chosen the following sizes so that I should be able to link them together to find a pattern and to prove my predictions right.

I have set out this table to help me understand and lay out the information about the size of the cubes. This information will help me in my predicted as the cubes are also related, so that a pattern should form.

Prediction

I predict that the cube that has the largest surface/volume ratio will diffuse the quickest in the acid (cube 4).

I predict that the cube that has the smallest surface/volume ratio will diffuse the slowest in the acid (cube 1).

I have noticed that cube 4 is twice the size of cube 1 ...

This is a preview of the whole essay

Prediction

I predict that the cube that has the largest surface/volume ratio will diffuse the quickest in the acid (cube 4).

I predict that the cube that has the smallest surface/volume ratio will diffuse the slowest in the acid (cube 1).

I have noticed that cube 4 is twice the size of cube 1 in terms of surface/volume ratio. Cube 4 is 12 and cube 1 is 6. From this information I would predict that cube 4 should diffuse twice as quick as cube 1.

I have made these predictions by using the secondary sources of my class work, SEG science revision guide and the Internet. The information, which I obtained from the Internet, was from the site . From this site I found information on similar experiments, this also helps explain the diffusion theory. The class work on the 10th January helps me understand what happens scientifically between the gelatine and the Hydrochloric Acid. The revision guide gives other experiments where diffusion occurs and in formation on rate of reactions with the amount of surface area.

Diffusion is when the particles in a liquid or gas spread out evenly within the whole of the container. The particles in the Hydrochloric Acid want to fill the whole of the liquid inside the test tube. But in the test tube there is the gelatine, which gets in the way, so the Hydrochloric Acid particles diffuse slowly into the gelatine so that it covers the whole of the solution. The larger the surface/volume ratio of the gelatine the quicker it is for the acid to diffuse completely into it. Also the smaller the surface/volume ratio of the gelatine the slower it is for the acid to diffuse completely into it. This is because the more gelatine that is exposed to the acid means that there are more Acid particles that collide with the gelatine. When the Acid particles collide with the gelatine, they diffuse into it, so the more collisions then the quicker the rate of diffusion.

Biology Coursework

OBTAINING

Time Taken for Acid to diffuse

From the graph I have drawn from the results table above it can tell me a lot of information about the experiment. It shows that there is a negative correlation from which a curve has been drawn. The graph shows that my prediction was correct in that the larger the surface/volume ratio then the quicker the Hydrochloric Acid will diffuse into the whole of it.

CONCLUSION

The results show that there is a pattern between surface/volume ratio and the time taken to diffuse. The smaller the surface/volume ratio the longer the time taken to diffuse. The larger the surface/volume ratio the shorter the time taken to diffuse. There is also a curve that I have been able to draw on the graph that links all of the experiments together.

When comparing the results with each other I have found that:

From these results I cannot really find a definite pattern. The surface/ volume ratio 6 is about 4 times as large as 12, when I predicted it to be around 2 times. I have found that the ratios 8,10 and 12 are really close together when ratio 6 takes much longer than what I would expect.

The Hydrochloric Acid diffuses into the gelatine because the acid wants to fill the whole of the area it is in. the diffusion happens slower with a smaller surface/volume ratio because there is more gelatine inside which isn’t exposed to the acid. The low number of this ratio leads to less particles in the Hydrochloric Acid to collide with the gelatine, so makes the process of diffusing slower.

My results show that most of my predictions were correct. The larger the surface/volume ratio the quicker it diffused was correct. This is true because more acid particles can collide with the gelatine, as there is a big surface area for its volume. Also my prediction the other way around was correct by a small surface/volume ratio would take longer. This is because is has a smaller surface area for its volume and so less acid particles collide and react. My prediction on the ratio 12 being twice as quick as ratio 6 cannot be proven correct, though I know that it is. My results show that it is about 4 times as long instead.

Diffusion in living creatures would take a long time because they are so large and would have a small surface/volume ratio. This is why animals have respiration systems with lungs where they are able to inhale much oxygen than it was to be diffused.

EVALUATION

Overall I think that the experiment and results worked well. The plan of cutting the cube was a bit difficult because I do not think that it was a very accurate way to cut them. This may have a knock on effect to my results. My results were as I expected apart from the one with the smallest surface/volume ratio. This took a lot longer to diffuse than I would have expected. I think that it may be because of inaccurate cutting. It may also be inaccurate because I noticed that this cube was larger and one side of it stuck to the bottom of the test tube. To solve this I could have used more acid or a larger test tube. Other ways in which this result may have been not accurate might include the fact of my warm hands could have altered the temperature of the acid; I could have put it on a clamp stand instead. Also some of the blocks stuck together for a short while which would have altered there surface/volume ratio, to prevent this from happening I could have done each of the cubes separately but this would have took a lot longer to do. All of my other results were accurate because the 2 different times were similar.

I think that my line of best fit would be fairly reliable apart from the start where the result is a bit wrong. My judgement on when the cubes diffused I thought was very accurate. I think that I could use 10ml more of acid to make sure the large cube is fully under the acid. Also I think that I chose the right size cubes as I could easily compare them.

I don’t think all my results are reliable, especially surface/volume 6 as it doesn’t fit the pattern. Other ways in which I could do the experiment include different shapes, triangles, and spheres. Though these would be very hard to cut and hard to find out the surface/volume ratio of them. I could also change the variable and change the temperature of the concentration of the acid to see what differences these would have made.