Information on Osmosis.
A French botanist, who prepared plants cells to study them between 1824-30, he looked for cells in animals, but was unable to find any. He also discovered and named the phenomenon of , which is the passage of a liquid through a semi-permeable membrane. Dutrochet was the first to carefully study respiration and light sensitivity in plants.
is the phenomenon of water flow through a semi permeable membrane that blocks the transport of salts or other solutes through it. Osmosis is a fundamental effect in all biological systems. It is applied to water purification and desalination, waste material treatment, and many other chemical and biochemical laboratory and industrial processes.
When two water (or other solvent) volumes are separated by a semi permeable membrane, water will flow from the side of low solute concentration, to the side of high solute concentration. The flow may be stopped, or even reversed by applying external pressure on the side of higher concentration. In such a case the phenomenon is called reverse osmosis.
If there are solute molecules only in one side of the system, then the pressure that stops the flow is called the osmotic pressure.
The movement of a solute molecule within a solvent is over damped by the solvent molecules that surround it. In fact, the solute movement is wholly determined by fluctuations of the collisions with nearby solvent molecules. However, the average thermal velocity of the molecule is the same as if it were free in a gas phase.
Whenever a solute movement is blocked by a wall it will transfer momentum to it and, therefore, generate pressure on it. Since the velocity is the same as that of a free molecule, the pressure will be the same as the pressure of an ideal gas of the same molecular concentration. Hence, the osmotic pressure p is given by formula:
p = cRT
Where c is the molar solute concentration, R is the gas constant, and T is the absolute temperature. This formula is the same as the pressure formula of an ideal gas.
Diagram 2 shows connected vessels separated by a semi permeable membrane. If there is only water in the device, the level will be the same at both sides. When solute molecules are added to one side, water will start to flow into it, so that its level will go up at this side, and down at the other side. The system will stabilize when the osmotic pressure is balanced by the hydrostatic pressure generated by the difference in the water levels.
Osmosis is a reversible thermodynamic process. That is, the direction of water flow through the membrane can be reversed at any moment by proper control of the external pressure on the solution. Contrary to that, the process of mixing a teaspoon full of sugar in a cup of tea is an irreversible thermodynamic process. There is no way to reverse the process at any given moment and un-mix the sugar back to the spoon
Obtaining evidence
The table on the next page contains the measurements of each piece of potato before the experiment and the results from after the experiment.
The table on the next page shows the averages of the above results. On the next page is a graph of these average results.
The higher the sugar concentration in the liquid solution the lower the average of weight, length and width results... All weights before the experiment were 1.6g, the length and width of the potato pieces were all the same. All experiments were attempted 3 times and all were left for the same period of time.
Evaluation of experiment
We followed the plan correctly; I believe we gained accurate and sufficient enough results to conclude the experiment, and to prove our hypothesis.
My final results were very reliable, due to the precautions I took to make this a fair test. Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results; so that we can make sure the results are totally correct.
Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tell us how much water could be transferred for each solution.
Repeating the same tasks more than three times would not have affected the results as all the results were very close. Overall, given the apparatus that we got to carry out the test, I think this experiment turned out to be very successful.
