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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
X 100
To Calculate the % change in mass:
Period 4 Lab 1B Data
% Change In Mass Period 6
M A B C D E Class av.
1.00.80.60.40.2
0.0
Period 5 Lab 1B Data
% Change In Mass Period 6
M A B C D E Class av.
1.00.80.60.40.2
0.0
Contents in Dialysis Bag Initial Mass Final Mass MassDifference Percent Change in Mass
a) 0.0 M Distilled Waterb) 0.2 M Sucrosec) 0.4 M Sucrosed) 0.6 M Sucrose e) 0.8 M Sucrosef) 1.0 M Sucrose
Period 4 Lab 1C Data
Contents in Dialysis Bag Initial Mass Final Mass MassDifference Percent Change in Mass
a) 0.0 M Distilled Waterb) 0.2 M Sucrosec) 0.4 M Sucrosed) 0.6 M Sucrose e) 0.8 M Sucrosef) 1.0 M Sucrose
Period 5 Lab 1C 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
Lab 1C: Ideal Class Data
Sample Best Fit % Change in Mass of Potato Cores at Different Molarities of Sucrose
-25
-20
-15
-10
-5
0
5
10
15
0.0 0.2 0.4 0.6 0.8 1Sucrose Molarity within Beaker
Perc
en
t C
han
ge
Data Set Best Fit
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
= p + s
Where there is no % change in mass, the solution in the
beaker has the same water potential as the potato cells.
(= p + s) = (= p + s)
Beaker Potato
p = 0 (open beaker) so s
To Calculate s
• See page 13 of the labs = -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 (0.0831 liter bars/mole °K
T = Temperature °K (273 + °C)
So lets say the line of best fit crosses the x axis at 0.36……..
s = -iCRT
s = -(1.0)(0.36 mole/liter)(0.0831 liter bar/mole ° K)
(295 ° K)
-8.83 bars
This equals the entire of the cell