We made the solutions by setting up 12 test tubes then we made a range of salt and sugar solutions of different water potentials, how we made the solutions are as follows.
To make the chips we got a potato and we chopped 12 identical chips from only the one potato. We tried to make them approimetly 4x1x1. Soon after that we placed the each of the 12 potato chips into each of the 12 test tubes, but we had to mark down which chip went in which solution as the chips were not all the same weight. We also had to write down the time they entered the solution. We then left the chips in solution for 50 minutes then we took them out as well as drying and weighing the chips again, and wrote down the results (weights).
Diagram
Results
Sugar
Salt
During our experiment we did things for certain reasons:
- We dried the chips off with a paper towel so that no excess water was accounted for when we weighed them.
- We only used the one potato when making the chips because we had to make sure each of the chips had the same water potential; the experiment would of been wrong if we used another potato of different water potential
- We had to make sure that we used 3 syringes when making the solutions; this was because we did not want to cause any cross contamination between the salt/sugar and water solutions because our results would be affected, as the osmotic effect of the solution would alter.
- We also had to mix the solutions thoroughly so that there was the same ratio of water and salt/sugar within the solution we did this because we wanted the whole solution to have the same water potential.
- We had to keep the chips the same size (4x1x1), as we wanted each potato chip to have the same water potential if the size was altered there will be a difference in water potential within the chips.
- We used percentage change in mass because it was a much more accurate way of comparing salt to sugar in different concentrations of solutions.
From my results / graph and I have found out that, in dilute solutions the chips gain weight, as there is a high water potential within the solution, so water enters the chips via osmosis. However in concentrated solutions the chips loose weight because the solution has a lower water potential, so the water leaves the chips via the process of osmosis. Also by looking at my graph I can see that salt is more osomotically active than the sugar. For example in the 0.5 molar solutions, a chip in the sugar solution looses 19.6% of its weight whereas a chip in the salt solution looses 39.9% of its weight. And by looking at the graph I can see the line of best fit goes further down the y-axis than the line for sugar therefore there it shows me there is a larger percentage change for salt.
There is a reason for the difference in water potential between salt and sugar solutions. Salt is much more osomotically active than sugar because its splits into to ions for example NaCl splits into Na+ Cl- hence it has twice the osmotic effect. Sugar just stays as one molecule. Here is a diagram to help explain:
By looking at my graph I can estimate the water potential of potato tissue. It is equivalent to 0.11M in salt solution and 0.18M in sugar solution.
However there were a couple of anomalies in my results. The chip that entered the 0.3M solution produced a large drop in its mass compared to the chips within a higher concentrated solution, the reason why it dropped so greatly was that it was a very large chip, this meant that more water was inside the chip therefore it diffused out to reach an equilibrium of water potential.
During the experiment there was one thing in particular which affected our results. It was the shapes of the potatoes they were hard to cut the same size as the knife was quite blunt, so we ended up with sum large potatoes like the one that went in the 0.3 molar sugar solution. This dint fit in with the line of best fit, therefore the water potential of the sugar solution mite of been slightly different to what we stated earlier. A way, in which we could resolve this problem, is re-doing the experiment using a cork borer. This would of made the chips the same thickness so all that we he would have to do is make sure the lengths are the same.
Another limitation of the experiment is that when we made the solutions it was hard to get the exact amount of water and either sugar/salt, this was because the pipette that we used dint show clear volumes on it and they were not very precise, this only effected our results slightly therefore did not really effect our conclusions.
