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