Charlie Matthews 10C 5/2/2007
An Experiment to investigate the mass and surface area of potato chips after being in different concentrations of NaCl.
- I predict that the percentage decrease in mass and surface area of the potato chips will decrease more as the percentage of NaCl is increased.
-This is because the NaCl solution has a higher concentration and lower water potential than the potato, which has a low concentration and high water potential. Therefore I predict osmosis will occur. I define Osmosis as the movement of any solution’s molecules from a place where they are highly concentrated to a region where they are in lower concentration. These molecules must pass through a semi permeable membrane (in this case the cell wall), which lets through smaller molecules but not larger ones. So water molecules from the potato will pass through the cell wall to the NaCl solution.
My prediction will only be correct if the skin of the potato is removed, as skin is not semi permeable.
I based my prediction on information from “Biology for You”-Gareth Williams, p21+
I predict that a graph of my results will look as following:
- I will be controlling the % of concentration of NaCl that the potatoes are placed in. I will be using five different concentrations. I found from my pilot study that to gather evenly spread, clear results, I decided to use: 2%, 4%, 6%, 8% and 10%.
- I will be aiming to keep the original size of the fifteen potato chips I will be using, the same (therefore the surface area also) In my pilot study I found that making each 4cm long with radius 7mm,was an adequate size for my investigation, I also found that using these dimensions I could fit three potato chips in each glass beaker without them touching each other (possibly altering the results)
- I have decided that I will weigh them individually as well as aiming to keep their masses the same as due to human error they will not all be the same mass/surface area.
- I will also be keeping the period of time in which the potatoes are kept in the solutions the same. In my pilot study I found that twenty minutes was enough time for the results to show a clearer trend, and that in the double lesson specified for the practical, twenty minutes would give me ample time to weigh my potato chips after and record and calculate the surface area.
- I found in my pilot study that by recording both surface area and mass, if one went wrong, one could support the other. If an object decreases its surface area, it must decrease its mass as well. So even if one experiment produced many anomalies and unclear data, the results from the other could still support my prediction.
- I will not be accurately controlling the temperatures in the room when my experiment is being carried out. But in my pilot study I found that it is best to complete all the investigation at the same time, with all windows closed to avoid vagueness in my results and avoid anomalous data.
