Experiment of Osmosis in Potato Chips

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.

In solutions with a sugar concentration less that 0.3 mol L-1 the water potential of the solution inside the cell is still lower than that of the surrounding sugar solution so water moves into the potato cells by osmosis. In the 0.3 mol L-1 solution the water potential of the solutions inside and outside the cell are very similar so there is very little net flow of water into the potato cells as can be seen by the relatively small gain in mass of the potato chips.

As the concentration of the sugar solution increases from 0.3 to 0.7 mol L-1 the potato chip loses more and more mass because the difference in water potential between the inside of the potato 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 sugar concentrations but lost mass in high concentrations of sugar. 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 potatoes.

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 test tubes with gladwrap and keeping them in the fridge for 12 hours.

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