1. Water Potential
Ψ = Ψp + Ψs
Water Potential Video

3. what is water potential?
The potential energy of water compared to pure water
Mathematical way to determine the movement of water (osmosis)
Water always moves from areas of _______ water potential to areas of _______ water potential 3

4. Water Potential Equation
Ψ = Ψp + Ψs

5. Pressure Potential
In an open Container/beaker, the pressure potential is _________bars

6. Solute Potential Osmotic Potential
Distilled Water (Pure Water) has a solute potential of _____ bars. Why?

7. What happens to the number of “free” water molecules available as the salt crystal dissolves?
This explains why solute potential is always __________ (one exception…)

8. How can you determine the ionization constant of a substance?

9. How does increasing the concentration (C) change the magnitude of the solute potential of the solution?

10. Calculate the solute potential of a 0
Calculate the solute potential of a 0.4M sucrose solution at 25 degrees C

11. If the sucrose solution from the previous example is in an open beaker, what is the pressure potential of the solution?

12. What is the water potential of the solution?

13. If a sample of potato cells with a water potential of -4
If a sample of potato cells with a water potential of -4.9bars is placed in this solution, in which direction will osmosis occur? WHY?

14. How do we know which direction water will move?
TOWARDS THE HIGHER SOLUTE CONCENTRATION (from high water potential to low water potential) 14

15. Ψs = Solute Potential (tonicity)
Ψp = Pressure Potential (external force)
The units for Ψ are pressure units. Typically bars (torr or mmHg)
If a system is at atmospheric pressure, Ψp is 0 (and therefore water potential = solute potential)
Ex: A solution in a beaker of water

16. When a cell is in equilibrium with its surrounding solution, the water potentials of them are EQUAL!! 16

17. Ψs Solute (osmotic) potential
Pure water has a solute potential (Ψs) of zero. Solute potential can never be positive.
Adding more solute is a negative experience; the solute potential becomes negative.

18. Solute potentialΨs = − iCRT
i = The ionization constant for the solute
for sucrose or glucose, this number is 1
For NaCl, it would be 2 (Na+, Cl-)
C = Molar concentration of the solute
R = Pressure constant = liter bar/mole K
T = Temperature in Kelvin (273 + °C)

19. Water potential Figure: 32.1c Caption:
(c) If wall pressure is very high, it can counteract the tendency of water to move via osmosis as in the example given here.

20. In which direction will the water move?
Ex: The initial molar concentration of the cytoplasm inside a cell is 2M and the cell is placed in a solution with a concentration of 2.5M.
Is the solute potential is more negative inside of the cell or in the solution?
In which direction will the water move?
Will the cell increase or decrease in mass?
What is the pressure potential of the cell? Of the solution?
Is the cell hyper, hypo or isotonic to the solution?

21. Practice Problem
The molar concentration of a sugar solution in an open beaker has been determined to be 0.3M. Calculate the solute potential at 27 degrees. Round your answer to the nearest hundredth.

22. The pressure potential of a solution open to the air is zero
The pressure potential of a solution open to the air is zero. Since you know the solute potential of the solution, you can now calculate the water potential.
What is the water potential for this example? Round your answer to the nearest hundredth.

23. Practice Problem
Determine which of the following solutions will gain the most water if placed into a sample of pure water in a piece of dialysis tubing at the temperature indicated:
Solution
Solute
Concentration (C)
Temperature A
Sucrose 2M
298K B
NaCl 1M
290K C
Glucose
27 C