# Diffusion and Osmosis.

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Diffusion and Osmosis

Diffusion and Osmosis Overview
You will investigate diffusion and osmosis in a model membrane system You will investigate the effect of solute concentration on water potential as it relates to living plants.

Concentration Effect

Molarity C6H12O6 = glucose Sucrose = 2 glucose C6H12O6 + C6H12O6 =
C6H12O6 - H2O = C12H22O11 so Using the periodic table, you can calculate GFM of sucrose (342g)

So to make 500 ml of solution…….
0.0 Molar = 342g x 0 x .5 0.2 M = 342 x .2 x .5 etc

Prepare dialysis bags……
Add sucrose solutions to bags Mass carefully Place in distilled water for 30 minutes Re-mass Calculate the % change in mass

Final Mass-Initial Mass Initial Mass
To Calculate the % change in mass: Final Mass-Initial Mass Initial Mass X 100

Period 4 Lab 1B Data % Change In Mass Period 6 M A B C D E Class av. 1.0 0.8 0.6 0.4 0.2 0.0

Period 5 Lab 1B Data % Change In Mass Period 6 M A B C D E Class av. 1.0 0.8 0.6 0.4 0.2 0.0

Period 4 Lab 1C Data

Period 5 Lab 1C Data

Lab 1C: Ideal Class Data Contents in Beaker % Change in Mass
Distilled Water 21.4 0.2 M Sucrose 6.9 0.4 M Sucrose - 4.5 0.6 M Sucrose - 12.8 0.8 M Sucrose - 23.0 1.0 M Sucrose - 23.5

LinearFit for: Data Set
Percent Change in Mass

Water Potential In Potato Cells
Osmosis is a special type of diffusion. It is the movement of water molecules through a selectively permeable membrane from a region of higher water potential to an area of lower water potential Water potential is the measure of free energy of water in a solution Water always moves to a more negative water potential.

Water Potential = Yp + Ys
Where there is no % change in mass, the solution in the beaker has the same water potential as the potato cells. (Y = Yp + Ys) = (Y = Yp + Ys) Beaker Potato Yp = 0 (open beaker) so Y = Ys

To Calculate Ys See page 13 of the lab Ys = -iCRT
i = Ionization constant (sucrose is 1.0 because it does not ionize). C = Molar Concentration (from line of best fit where the line crosses the x axis) R = Pressure Constant ( liter bars/mole °K T = Temperature °K (273 + °C)

So lets say the line of best fit crosses the x axis at 0.36……..
Ys = -iCRT Ys = -(1.0)(0.36 mole/liter)( liter bar/mole ° K)(295 ° K) -8.83 bars This equals the entire Y of the cell