Investigate Osmosis In Potato Chips.

? The cylinders will be dried to remove any excess water.

? The saltwater solutions will have concentrations of: 0 moles (distilled water); 0.2m; 0.4m; 0.6m; 0.8m and 1m. I will make the solutions by mixing:

Solution

Saltwater

Water

0 m

0

parts

with

part

0.2 m

2

parts

with

8

parts

0.4 m

4

parts

with

6

parts

0.6 m

6

parts

with

2

parts

0.8 m

8

parts

with

2

parts

.0 m

0

part

with

8

parts

? The solutions will be mixed in a test tube before going into the Petri dishes.

? This is the fixed variable. There are more variables so that I get a better and more accurate graph, from which I will be able to clearly identify the concentration of saltwater where osmosis stops. (This will be the isotonic solution, and from this I will be able to ascertain the water potential)

? The solutions will be measured with a graduated pipette so that I have maximum accuracy of liquid amounts. It will be used both when creating the solutions and when measuring the amount to go in each Petri dish.

? There will be lids on the Petri dishes so no water can evaporate, because this would change the concentration of the solutions.

? 3 potato cylinders will be placed in each solution so I can have a good average, and if one result is anomalous I will still have two other results to go on. They will be placed in the exact same solution so I can be sure they undergo the same conditions. Each lid will be labelled with which cylinder it is above so I don't use the wrong initial weight to work out its percentage change from the original.

? All of the Petri dishes will be exposed to the same light, temperature and pressure, as they will be left in the same area of a room. Although these variables will not be constant they will be the same, e.g. if a light is switched off they will all have no light.

? All the Petri dishes will be left for 3 hours before they are weighed. This should give ample time for a real difference to be seen without the potato cylinder pulverizing or decomposing.

Showing my results:

I shall show my result by the weight gained of lost from the potato cylinders after being removed from the solutions rather than the volume of water gained of lost from the solution after the potato because I feel the results will be more drastic and less complicated to show.

When I have found the end weight I can make a table for quick view to show my results like this:

Solution

Chip

No.

Original weight

Final weight

Increased

or

Osmosed

in or out

Percentage changed from

(moles)

mg

mg

decreased

of potato

Original %

I will work out the percentage change from the original by dividing the final weight by the original and multiplying by 100.

Percentage change from original = final weight x 100

original weight

I shall find the percentage change for each solution if the results are all close. If one is radically different I can reject it and use the other two. I shall find the average by simply adding up the percentage change and dividing by the number of results I added. I will put the averages on a simple table like this:

Solution

Chip no.

Initial weight

Final weight

Percentage change

Average percentage

Moles

mg

mg

%

change %

0

2

I shall put my results on a graph, with solution on the horizontal axis and percentage changed from the original on the vertical. I will plot the average percentage for each solution and mark the 100% line. Where the graph line hits the 100% line the solution will be isotonic for this type of potato and I can see the water potential of the potato cells.

These are the water potentials for each solution:

Table 3

Solution

Water potential

0m

0

0.2m

.5184 MPa

0.4m

.0368 MPa

0.6m

2.592 MPa

0.8m

3.456 MPa

.0m

4.32 MPa

At the point where the concentration of the solution is equal to that of the potato cell I can find out the water potential of the potato cells by multiplying the concentration by 4.32 MPa. I can check if this is right by ensuring the answer is between 0 and 1.5185 MPa.

Water potential = concentration x 4.32 MPa

Planning

Bekki Le Prevost Science Mock Coursework 4/11/01

Page 2

Planning

Bekki Le Prevost Science Mock Coursework 4/11/01