Diffusion and Osmosis

Diffusion of Ammonium hydroxide with red litmus paper

Definition of diffusion

1. Diffusion is the process in which particles move from an area of high concentration to an area of low concentration in order to evenly spread out.

2 Diagram.

3. During the diffusion tube experiment I noted that firstly ammonium hydroxide was placed on to a piece of cotton wool. The cotton wool (with the ammonium hydroxide) was then placed in to a diffusion tube containing around 10 pieces of curled red litmus paper lined up from one end of the diffusion tube to the other.
I had observed the diffusion tube carefully when approximately a minute later I noticed the first litmus paper had changed colour from pink to blue. About five minutes later the second red litmus paper in line had also changed from pink to blue. Two days later the entire tube had changed colour from pink to blue, thus proving that diffusion had occurred.

4. Using my knowledge of diffusion I can easily state that the change of colour the red litmus paper had (from pink to blue) occurred through the act of diffusion.
This was due to the fact that there was a high concentration of ammonium hydroxide on the cotton wool, yet a low concentration of ammonium hydroxide on to the red litmus paper.
The ammonium hydroxide particles (on the cotton wool) had moved through a concentration gradient, from an area of high concentration (the cotton wool containing ammonium hydroxide) to an area of low concentration (the red litmus paper.)
Eventually all the red litmus paper had changed colour showing that all their particles had become evenly concentrated with the ammonium hydroxide.

5. In my opinion if a higher concentration of ammonium hydroxide had been used then the process of diffusion would have occurred faster. I predict that because, there would have been a higher concentration of ammonium hydroxide on to the cotton wool which means that there would have been an increase of ammonium hydroxide particles and the more particles there are then the more there would be to penetrate the red litmus paper thus speeding up the act of diffusion.

b. If the experiment would have been done at a higher temperature I believe that the process of diffusion would have been a lot faster. I base that view on the theory that at a higher temperature particles move faster and therefore would most likely escape the concentration of ammonium hydroxide faster and spread throughout the diffusion tube at a faster rate.

6. If the ammonia would have been left in the tube for 24 hours then the concentration of ammonia hydroxide would have been evenly spread inside. This would have occurred because the ammonium hydroxide particles would have had the necessary time to diffuse onto the red litmus paper. This would be visible by seeing that all the red litmus papers changed colour from pink to blue.

7.1. Diffusion occurs in a single celled organism that lives in the water called an Amoeba. The level of oxygen inside the water is high yet the level of oxygen inside the amoeba is low.
Whenever the Amoeba breathes in it inhales the oxygen from the water, in which case the oxygen goes from an area of high concentration (the water) to an area of low concentration (the amoeba).As the amoeba breathes in the oxygen it creates carbon dioxide as a by product to the oxygen it takes in, therefore the amoeba contains high concentration of carbon dioxide. In that case the carbon dioxide diffuses from an area of high concentration (the amoeba) to an area of low concentration (the water).

7.2. Animals need oxygen to live and the way the oxygen gets transported throughout their bodies is diffusion. After inhaling oxygen the animal's lungs carry a high concentration of oxygen yet the animal's organs contain a low concentration of oxygen. The oxygen from the lungs then travel from an area of high concentration (the lungs) to an area of low concentration (the organs). After inhaling oxygen the animals body produces carbon dioxide as a by product, so now the animal has a high concentration of carbon dioxide yet the air has low concentration of carbon dioxide so the carbon dioxide moves from an area of high concentration (the animal) into an area of low concentration (the air).

Osmosis in potato chips experiment

8.Osmosis is the diffusion of water molecules from an area of high concentration of water to an area of low concentration of water through a partially permeable membrane.

Concentration
(m) Initial mass of potato (g) Mass of potato after 30mins (g) Mass change of potato (g)
A 0 3.3 3.5 0.2
B 0.1 3.4 3.6 0.2
C 0.3 3.6 3.7 0.1
D 0.5 3.3 3.3 0
E 1.0 3.2 3.1 - 0.1 10.

12. When observing the graph I notice that there is a distinct pattern. There is a mass decrease in the potato the higher the concentration of sucrose and a mass increase the lower the concentration of sucrose. When the concentration was below zero then the mass increased due to there being no partially permeable membrane there to stop the water from diffusing into the potato. When the potato was in a concentration higher than zero then the sucrose was able to act as a barrier and prevent some and eventually all the water from entering the potato, therefore the mass of the potato gradually decreases. On the graph when the concentration was at 0.5 the mass of the potato remained the same therefore that was the point at which they were at equilibrium.

13. 1. The potatoes in solutions (A), (B) and (C) had gained weight and each has its individual reasons. For example: If observing the potato in solution (A) there is a clear increase in the potatoes weight, that is because there was no partially permeable membrane in that solution so the water was able to easily diffuse into the potato. If looking at the potatoes used in solutions (B) and (C) there was a considerable rise in the potato in solution (B) yet a smaller rise in the potato in solution (C). That was because the level of sucrose in comparison to the water was low in the potato in solution (B) so the water was able to diffuse with the potato as if there was none or very little barrier. The concentration in solution (C) was higher so the partially permeable membrane (sucrose) was able to prevent some of the water from diffusing into the potato, but not all.

13.2. The reason why some chips lost weight can be explained if observing the potato in solution (E). In the potato in solution (E) the sucrose concentration was higher than the water, In which case there was no way for the water to diffuse into the potato. The potato now had the high concentration of water and the sucrose had the low concentration of water in which case the water from the potato diffused into the sucrose minimizing the weight of the potato making it shrink and lose water in which case it lost 0.1 grams in mass.

14. The reason there was no weight change in the potato in solution (D) is because there was just enough sucrose in the solution that allowed the sucrose to act as a partially permeable membrane and sucrose in the solution. This caused the sucrose to be able to act as a partially permeable membrane and prevent any water from entering the potato.

15. There are many errors and limitations that may occur when conducting scientific experiments, I am aware that some of these errors and limitations may have impaired my findings. The following are the main limitations that I may have encountered while doing this experiment:

• The first error I had encountered was that I could have measured the length of each of my potato pieces before starting and after completing the osmosis experiment. This was not a very significant error but it could have been beneficial in order to keep a record and compare the size of my potatoes before and after the experiment.

• I noticed that I had different weights of potato chips when starting the experiment and that I only recorded the mass change of the potato chips. In order to have achieved completely accurate results I should have made sure to have the same weight of potato chips at the start of the experiment and I should have calculated the percentage change in the potatoes mass instead of just the mass change. My potatoes didn't vary that much in size though the heaviest potato I had was 3.6 grams and the lightest was 3.2 grams therefore I don't feel that this error affected my results to significantly.

• I noticed was that when removing the potato chips from the boiling tube I had to poke a hole in each of the potatoes to get a hold of them and this may have caused me to squeeze out a little too much liquid from inside the potatoes or maybe some liquid that had diffused into the potato. I also had to dry up any excess liquid that may have been on the potatoes because if any liquid got on the scales when measuring the potatoes It could have led to inaccurate results. I feel that these errors could have had significant affects on my final results.

• My experiment could have been completely accurate if I had repeated every process of the experiment a minimum of three times. By doing this I would have been able to notice any obscure results and be able to calculate the mean value of my results.

16. I feel as if I took as much precaution as possible when dealing with this experiment yet there was still a chance some errors may have occurred. In order to achieve more accurate results I would do the following:

• Firstly collect all the equipment necessary and organise everything in the best possible order.

• Place test tubes into the test tube rack and label them accordingly (A, B, C, D, and E).

• Get one potato and cut all the potato chips you will use from the same potato.

• After cutting the potato pieces measure their length with a ruler in order to make sure that they are all of accurately the same length.

• Place the potatoes one by one on a scale (g) but make sure that there is nothing else on the scale and that the scale is set on zero before placing the potatoes on it.

• After the potatoes have been cut and measured pour the correct solutions into the correct test tubes and then place the potatoes chips one at a time into the correct test tubes, make sure they are all placed fairly quickly one after the other for more accuracy and make sure what time they were placed in the test tubes.

• When removing the potatoes from the test tube do it as carefully as possible making sure not to squeeze out to much liquid from the potatoes yet make sure not to leave too much liquid on the potatoes.

• Place the potatoes one by one on the scale in order to record their weight and add the results to your table.

• Make sure to calculate the mean value for all of your results and to calculate the percentage mass change and the length change of the potato chips.
After making the necessary calculations present them in a table and on a graph with a line of best fit.