Diffusion gradient
This diffusion gradient shows which direction the water molecules will move when there is a high concentration of salt solution.
This diffusion gradient shows which direction the water molecules will move when there is a an equal solution of salt and water
This diffusion gradient shows which direction the water molecules will move when there is a low concentration of salt solution.
Apparatus-In this experiment I am going to use:
- Stop watch
- Water
- Measuring cylinder
- 10 test tubes
- scales
- knife
- potato chips
- 2 molar salt solution
Diagram-
Preliminary work-We did preliminary work so we knew what we were going to be doing in the experiment and to see if we should make any changes in the experiment to make it more accurate. After doing the preliminary work we didn’t change anything in our investigation because the experiment worked well.
Preliminary results
Method-
- Cut and weigh 5 potato chips to the mass of 1.0 g
- Measure the 2 molar salt solution and water as shown in the table below
- Leave the potato chips in the 5 different test tubes of salt solutions for 15 minutes
- Weigh the potato chips
- Repeat experiment again
Fair test-To make this investigation a fair test I kept the weight of the potato chips the same, time the potato chips were left in the 5 different salt solutions and the same 2 molar salt solution.
Results-
Conclusion-My results show me my prediction was correct because osmosis occurred. Osmosis is a special kind of diffusion it is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration. The partially permeable membrane in the potato chip cell allows the passage of water molecules but not solute molecules (salt molecules) because it has tiny holes/pores in so only water molecules can fit through. The solutions with a low concentration of salt gained more weight because the water flows from the side of the membrane where the solution is weakest to the side where it is strongest, until the solution on both sides of the membrane are the same strength. There were no anomalous results in this experiment
Evaluation- Two problems in this investigation were when weighing the potato chips after 15 minutes, it was obvious that they would have excess water on them, and so I dabbed them with a paper towel to remove it. However, in doing this I could have removed water that was not excess, and altered my results.
Another inaccuracy was when I put the potato chips into the solutions, because it was impossible to not leave a small interval between each test tube. The first test would have been going for a few seconds longer than the last. To resolve this problem the people in my group could have all got a potato chip and put them in at the same time to make it more accurate.
To improve this investigation I could use potato chips with a larger mass, change the time the potato chips were in the solutions for and change the 2 molar salt solutions to give me a more accurate and wider range of results.
I think my results are fairly accurate because we weighed the potato chips on a scale which gave an accurate measurement and on the graph the points plotted are close to the line of best fit.
To extend this investigation further I could concentrate on a smaller range of concentrations around the point (on my graph) where there is no change in mass, to find the precise concentration that causes no change in mass.
