Fluffy Raisins- An experiment on Osmosis

Sam, 4th Grade

The topic of my investigation was osmosis. Osmosis is when a liquid moves from an area of greater concentration through a membrane to an area of lower liquid concentration. In a book I found an experiment that showed osmosis in action. You soaked a raisin in a cup of water overnight and the raisin got large and soft, more like a grape. I found this interesting but, it didn’t have enough of a question to do a whole experiment. I remembered seeing an experiment on the television shoe “Zoom” where kids did and experiment with liquids of different density. Density is the weight of a liquid per unit of its volume. In the experiment the kids used four liquids and placed them together in a clear glass container. Once the liquids had settled you could see they had separated into layers, with the densest liquid on the bottom and the lightest liquid on the top. I decided I could test some liquids with different density and see if it affected how fast osmosis would take place.

When I did my experiment I wanted to find out if the density of the liquid would affect osmosis. I also wanted to see if osmosis would occur quicker if I put holes in the raisins.

Before I started doing my experiment I realized I needed to learn more about osmosis and density. I went on the internet and found a website called “DiscoverySchool.com” and learned that osmosis is the movement of liquid from one solution through a special membrane into a more concentrated solution. A solution has two parts: a solute is a dissolved substance like salt in salt water, and a solvent which is the liquid such as water in salt water. During osmosis liquid moves through a semipermeable membrane, which is a membrane that allows solvent molecules to pass through its holes, but it blocks solute materials. Osmosis continues until the concentration on both sides of the membrane are of equal concentration. I learned that density is the weight of a substance divided by the volume of a substance. On “Zoom: I learned that of my four liquids syrup had the highest densitym next was salt water, then water, and finally vegetable oil.

To get started I gathered the following supplies: a needle, a log sheet, nine cups, raisins, water, vegetable oil, maple syrup, and salt water. I labeled the cups with the name of each liquid. I had a set of cups for the non-punctured raisins and a set of cups for the punctured raisins. I also had a cup for a raisin to be used as a control. Next I put the correct liquid in each cup. Then I picked nine raisins about the same size. Next, I poked a hole in one raisin for each type of liquid. Then I put the raisins in the correct cups (by whether or not the raisins had holes). Later, after the raisins had soaked overnight I took the raisins out and recorded any changes on my log. I examined the raisins again at four o’clock which was 24 hours and recorded the results. Finally, I repeated this procedure two more times to see if my results were accurate.

During my research I noticed that it didn’t seem to be density that affected how fast osmosis worked on the raisins. The raisins in the thicker solutions (syrup and vegetable oil) weren’t getting bigger, softer, or turning a lighter brown like the raisins in water and salt water were. I did more research and found that the thickness of a liquid is called viscosity. Viscosity is a fluids resistance to flow. The higher the viscosity the slower the fluid will flow. Example: Syrup has a higher density than water. I wondered if maybe viscosity has more of an affect on osmosis than density.

Next year, I thought it might be interesting to repeat my experiment with liquids of different viscosity and see if the raisins were affected in order of the different liquids viscosity. I learned about reverse osmosis while I was ding my research, This is where pressure is used to force water from salt water through a membrane into fresh water, the salt is left behind and more fresh water is made. That is backwards from the way osmosis would occur if there was no pressure. Ships carry kits that allow shipwreck victims to make fresh water from seawater. I thought it would be interesting to do an experiment on reverse osmosis.