Investigating Osmosis

Osmosis is the diffusion of water molecules across a semi-permeable membrane. Diffusion is the movement of molecules from an area of high concentration, to an area of low concentration. So, Osmosis is the movement of water molecules from an area where there are lots of water molecules to an area where there are few water molecules.

Our aim is to find the concentration of dissolved substances in the cells of a potato using Osmosis.

I predict that the potato in the higher concentration of salt solution will lose an increasingly high amount of weight. I think this because the higher the concentration in salt, the more water particles will move through the potato cell’s semi-permeable membranes to try and balance the salt concentration. For example, if you placed a larger piece of potato into a beaker of an almost 100% salt solution; the potato would completely shrivel up because it would lose all of the water molecules to the area of high concentration during Osmosis.

The range of different concentrations of salt and water solutions we are intending to use in order to find the concentrations of dissolved substances in the cells of a potato are:

· 0% (water)

· 0.5%

· 1.0%

· 1.5%

· 2.0%

· 2.5%

· 3.0%

The equipment that we are going to use for this experiment are:

· Seven test tubes

· A test tube holder

· Weighing scales

· Knife

· Clingfilm

· Pins

· A potato

Firstly, we will cut out 21 small pieces of potato all in the same size. We will then put the different concentrations of salt water into seven different test tubes; about a quarter of the test tube will be filled, just enough to cover three pieces of the potato. Next, one piece of potato will be weighed (and this weight will be recorded in a table) and placed in the 0% salt concentration test tube. A second piece will be weighed and recorded, then we will place a pin through the middle, then it will be put into the same test tube. A third piece will