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# Osmotic pressure

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Introduction

A study of osmosis Trevor Gotting Sept 30 2007 Ida Bailey Introduction: Osmosis is when water diffuses from an area of high water concentration to a low water concentration. Also there are various effects of solute concentration on cells, which we will be studying. In this lab we will determine how osmosis affects pieces of potatoes. Also we will see how much the change of mass the potato will end up after sitting in the solute. Hypothesis: If the concentration of solutes outside the potato is higher than the concentration of cells in the potato, the potato piece should shrink. Also if both concentration of cells from the potato and the solute are equal, then the potato shouldn't change. Lastly if the concentration of cells in the solute is lower than that in the potato, the potato should get larger. Materials: see page 80. Procedure: see page 80. Change in mass observation Test tube # Solute concentration Initial mass (g) Final mass (g) Change in mass (g) Percent change in mass 1 0 4.53 g 5.49 g 0.96 g 21.2 % 2 0.2 4.54 g 4.79 g 0.25 g 5.5 % 3 0.4 4.56 g 4.46 g -0.1 g -2.2% 4 0.6 4.53 g 3.67 g -0.87 g -19.2% 5 0.8 4.54 g 3.41 g -1.13 g -24.9% 6 1.0 4.55 g 3.41 g -1.08 g -23.7% Calculations: Analyze: 1. From the graph information it shows that the solute concentration of sucrose in the potato pieces was around 0.38. If a potato piece was put into a solution with the sucrose concentration of 0.38 it would be isotonic. 2. Shown on graph 3. Some potato sections lost mass because there is a higher concentration of sucrose in the solution than the potato. Therefore the water in the potato is escaping and trying to equilibrate the solution through osmosis, causing the potato to shrink (hypertonic). Some potato sections got bigger because there was a higher concentration of sucrose in the potato than the solute. ...read more.

Middle

I never repeated any readings for this preliminary experiment as it was only a trail experiment for me to fully understand what I was doing, get used to all the equipment which I was going to use and finally to find out what concentrations of sucrose solution will be needed for my main experiment. Results: Concentration of solution (M) Original Length (cm) Original Mass (g) 1.00 5.2 4.13 0.75 5.1 4.26 0.50 4.9 4.09 0.25 4.7 3.81 0.00 4.9 4.00 After 30 minutes: Concentration of sucrose (M) Length (cm) Change in length (%) Mass (g) Change in mass (%) 1.00 4.9 -5.8 3.90 -5.6 0.75 5.0 -1.96 4.10 -3.8 0.50 4.9 0 4.06 -0.7 0.25 4.7 0 3.94 +3.4 0.00 4.9 0 4.20 +5.0 After 60 minutes: Concentration of sucrose (M) Length (cm) Change in length (%) Mass (g) Change in mass (%) 1.00 4.9 0 3.73 -4.4 0.75 4.9 -2.0 3.98 -3.9 0.50 4.8 -2.04 3.98 -2.0 0.25 4.7 0 4.03 +2.3 0.00 5.0 +2.04 4.32 +2.9 After 90 minutes: Concentration of sucrose (M) Length (cm) Change in length (%) Mass (g) Change in mass (%) 1.00 4.7 -4.08 3.59 -3.8 0.75 4.9 0 3.86 -3.0 0.50 4.8 0 3.94 -1.0 0.25 4.7 0 4.10 +1.7 0.00 5.1 +2.0 4.39 +1.6 After 120 minutes: Concentration of sucrose (M) Length (cm) Change in length (%) Mass (g) Change in mass (%) 1.00 4.5 -4.2 3.47 -3.3 0.75 4.9 0 3.79 -1.8 0.50 4.8 0 3.91 -0.8 0.25 4.9 +4.08 4.81 +2 0.00 5.2 +2.04 4.41 +1.4 Overall change in length and mass: Concentration of sucrose (M) % change in length % change in mass 1.00 -13.4 -16 0.75 -3.92 -11 0.50 -2.04 -4.4 0.25 -4.08 +9.7 0.00 +6.12 +10.2 o Therefore I decided that I would use concentration of sucrose solution for my detailed experiment to be: 0.25M, 0.29M, 0.33M, 0.35M, 0.38M and 0.40M o For my detailed experiment I decided to replicate the experiment, so I could ensure that my results are reliable and to eliminate any errors which I could have possibly made. ...read more.

Conclusion

More strikes result to more molecules passing through the pores, which in turn results in net diffusion of water from the compartment with high concentration of water to that with low concentration of water. In osmosis, water flows in a response to differences in molarity across a membrane. The size of the solute particles does not influence osmosis. Equilibrium is reached once sufficient water has moved to equalize the solute concentration on both sides of the membrane, and at that point, net flow of water ceases. Here is a simple example to illustrate these principles: Aim To find out how the concentration of the sugar solutions affects the amount of water intake by potatoes. Equipment Beakers Measuring Cylinders 6 sugar solutions of different concentrations ranging from 0.0-0.5% Weighing machine to 2 decimal places Hypothesis Potatoes are plants and they have a general plant structure. It contains a plasma membrane which will is selectively permeable, allowing water and some solutes though except larger solutes and ions. I predict that the potato piece with the lowest concentration will take in the most water through osmosis. This is because the solution is dilute and there is less water in the potato and therefore there will be a net water movement from the solution to the potato. As the solution is dilute the water potential is at its highest. I also predict that the potato with the highest concentrated solution will absorb the least amount of water as there is a smaller net movement from the solution to the potato. This is because the solution contains less water and more sugar and therefore there will be less water movement from the solution to the potato resulting in the potato piece with the lowest mass. This is because there is a low water potential. Results 2 pieces 10ml solution used Concentration of solution Weight of potatoes before Weight of potatoes after 24hr Change in Mass (%) 0.0 0.8g/0.8g 2g/2g 250 250 0.1 0.8g/0.8g 2g/2g 250 250 0.2 0.8g/0.8g 1g/2g 125 250 0.3 0.8g/0.8g 2g/2g 250 250 0.4 0.8g/0.8g 2g/1g 250 125 0.5 0.8g/0.8g 1g/1g 125 125 ...read more.

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