Period 4 & 5 – Task 3 Write up: (1)Title and Purpose (2)Final step by step method that you used. (3)Observations and results (you can use the table to you put together in task 2 if you did it on a separate piece of paper) (4)Graph (you can use the graph you did in task 2 if you did it on a separate piece of paper) (5)Conclusion (6)Discussion (7)Evaluation

Kumara Chips and Salt Purpose/Aim: Kumara Chips placed in solution with high concentrations of salt (0.6 mol L -1 and 0.8 mol L -1 ), will lose mass as the chips will lose water due to osmosis. Kumara chips placed in solution with lower concentrations of salt (distilled water, 0.2 mol L -1 and 0.4 mol L -1 ) will gain mass as the chips will gain water due to osmosis.

Method: (1)Collect distilled water and salt solutions (0.2 mol L -1 ; 0.4 mol L -1, 0.6 mol L -1, 0.8 mol L -1 ) (2)Fill three of the plastic containers with 15 mL of the 0.2 mol L-1 solution. Clearly label each container with 0.2 and A, B and C. (3)Repeat with all the other solutions and the distilled water. (4)Cut 15, 2 cm length, kumara chips from the same kumara using the size 1 cm sized cork borer. (5)Blot each chip with a paper towel. (6)Weigh each chip and place each one in each of the plastic containers. Record the weight of the chip and the plastic container it has been placed in. (7)Put the lid on each of the plastic container. (8)Place all the containers on the same place on the back bench so they all experience the same changes in temperature. (9)Leave all the chips in the solution until next period ( 24 hours) (10)Remove each chip, blot it dry with a paper towel and reweigh it. Record the final weight against each of the plastic containers. Use the same electronic scales to ensure consistency.

Observations: The chips in the distilled water (0.0 mol L -1 salt concentration) looked slightly larger and felt firm. The chips in the 0.8 mol L -1 salt concentration solution were soft and flaccid. Results:

Salt Conc Mol L -1 Plastic Container Original mass (g) Final mass (g)Difference in mass (g) % mass change Mean % mass change O.0 mol L -1 A B C 0.2 mol L -1 A B C 0.4 mol L -1 A B C 0.6 mol L -1 A B C 0.8 mol L -1 A B C

Conclusion: My results showed that the kumara chips gained mass in distilled water and the low salt concentrations (0.2 mol L -1 ) and lost mass in the higher concentrations of salt (0.4 mol L -1, 0.6 mol L -1, 0.8 mol L -1 ). This is almost what I predicted except for the 0.4 mol L -1. This happens because water moves in and out of the kumara by osmosis.

Discussion: When the chips were put in distilled water they gain mass because the chips gain water from the surrounding solution due to osmosis. The process of osmosis causes a net flow of water, across the semi permeable membrane, along the decreasing water potential gradient from a solution with a high water- potential to one with a lower water potential. The chips gain water because the distilled water has a higher water potential than the chips. The graph shows that in solutions with a salt concentration less that 0.3 mol L-1 the water potential of the solution inside the cell is still higher than that of the surrounding salt solution so water moves into the potato cells by osmosis. In salt solutions of 0.3 mol L-1 the water potential of the solutions inside and outside the cell are very similar so we would expect very little net flow of water into the kumara cells. As the concentration of the salt solution increases above 0.3 to 0.8 mol L-1 the potato chip loses more and more mass because the difference in water potential between the inside of the kumara cells and the surrounding solution is increasingly different. This means that when the chips are placed in the higher concentration solutions more water will move out of the chips as the result of osmosis.

Evaluation: My results showed that the chips gained mass in low salt concentrations but lost mass in high concentrations of salt. This conclusion is justified because I use a number of ways to ensure I used the best method possible to make my investigation a fair test. For example I used a cork borer to make sure all the chips used were cut as close to exactly the same shape as possible. This meant that each chip had the same surface area available for diffusion of water across the semi permeable membranes of the potato cells. The repeats used showed similar results to each other. A change made to my original method was to make the chips slightly smaller than planned. This was because I had to get all 15 chips from the same potato so that I could control the variable of water potential in cells in different kumara. The method was carried out in a way that variables that could have changed the rate of osmosis, such as evaporation and temperature, were controlled by covering the plastic containers with a lid and keeping them in the same area and conditions for 24 hours.