Aim: – To prove the law of Osmosis with the help of a simple experiment
Materials Required:-
2 small bowls or cups
Water
Sugar
2 raisins
Pencil or pen
Procedure:-
Fill each of the bowls about half full of water and place them on a table or flat surface where they can sit for several hours without being in the way. Use a paper and pen to make a label for each bowl. One label should say “Dilute Sugar Solution” one should say “Concentrated Sugar Solution”. Next you want to add salt to the water in the bowl labeled “Concentrated Sugar Solution”. Keep adding sugar and stirring until no more will dissolve. In the bowl marked “Dilute Sugar Solution” add a small amount if sugar. Stir it until the sugar is completely dissolved. Now take the raisins and put one in each bowl. Keep the bowls aside for a few hours.
Observation:-
After a few hours, take the raisin out of the bowl labeled “Concentrated Sugar Soultion” and examine it. What do you see? It seems to have wilted, getting very soft and flexible. Rinse your fingers to get rid of any sugar and pick up the slice in the plain water. What do you notice about it? It is not wilted at all. In fact, it is even more rigid than it was when you put it in!
Why did it happen?
It has to do with the process called osmosis. The raisin is made up of tiny, living units called cells. Each cell is surrounded by a cell membrane which acts much as your skin does. It keeps the cells parts inside and keeps other things outside, protecting the cell. While this membrane stops most things, water can pass through it. The water tends to move towards higher concentrations of dissolved chemicals. That means that if the water outside the cell is sugary than the water inside, water will move from the inside of the cell to the outside. That is what happened to the raisin in the concentrated sugar water. As the water left the cell it was much like letting the air out of a balloon. As more and more of the cells lost water, the raisin became soft and flexible.
When you put the raisin into the plain water, the reverse happened. Water moved from the outside, where there was no sugar, into the cell where there was some. This caused the cells to swell up, becoming very stiff.
