1. Water Water Water Potential

2. What are you water potential?
Measures the tendency of water to leave one place in favor of another
Measured in bars
High water potential = water molecules can easily move about
Low water potential = water molecules cannot easily move about

3. Water Potential Pure water  water potential of zero
Determines where water is going to flow due to
Osmosis
Gravity
Pressure
Surface tension

4. Lets go to our packet ‘o funB

5. So What Does This Mean? The solvent is pulling the water toward it
High solute concentration = low water potential
Low solute concentration = high water potential

6. Review
Moves from hypotonic to hypertonic

7. Review Hypotonic Hypertonic Solution= less solute; more water
Cell= more solute; less water
Hypertonic
Solution= more solute; less water
Cell= less solute; more water

8. Lets go back to our packet ‘o funY Z

9. Temperature High temperature = more water potential
Why?
Low temperature = less water potential
Water molecules can move easily
Water molecules cannot move easily

10. What Will Happen? When you put a pipette in water?
What do you have to do to get the water out?
Water will go naturally up, against gravity, without pressure (-)
Put pressure on it (+)

11. Water Concentration of solute is related to osmotic pressure…
Pressure related to pressure potential…
Pressure raises water potential

12. The 3 Factors What affects water potential? Temperature Solutes
Pressure

13. ψp
Pressure Potential
A force that resists water flow due to a container (cell) being full.
Important in plant cells because they are surrounded by a cell wall
Water enters plant cell, its volume increases and the living part of the cell presses on the cell wall

14. ψp
Pressure Potential
The cell wall gives very little so pressure builds up…oh no!
This has the tendency to stop more water entering the cell and stops cell from bursting
When plant cell is inflated with water, it is turgid
Pressure potential is called turgor pressure

15. pull water up a tree...if i put pure water at the roots, the water will flow into the roots bc of osmosis and because the roots have mre solutes (-2 water potential) but the stems have a lower water potential (-6) the leaves have even lower (-15) and the atmosphere has a water potential of (-1000)
pulling forces are negative (water go toward it)
pushing forces are positive (pushing water away...move to other region)

16. Solute (osmotic) potential (ψs )= –iCRT
The number of particles the molecule will make in water; for NaCl this would be 2; for sucrose or glucose, this number is 1
C =
Molar concentration
R =
Pressure constant = liter bar/mole K
T =
Temperature in degrees Kelvin (273 + °C) of solution
Yikes, what's that??????
Example 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°C degrees. Round your answer to the nearest hundredth. What is the water potential?
Answer:
-7.48
Solute potential
= -iCRT
= -(1) (0.3 mole/1) ( liter bar/mole K) (300 K)
= bar
Water potential
= , so water potential = -7.48

17. pressure potential (ψp ) + solute (osmotic) potential (ψs)
Water potential (ψ ) =
pressure potential (ψp ) + solute (osmotic) potential (ψs)
Pressure potential (ψp):
In a plant cell, pressure exerted by the rigid cell wall that limits further water uptake
Solute potential (ψs):
The effect of solute concentration. Pure water at atmospheric pressure has a solute potential of zero. As solute is added, the value for solute potential becomes more negative. This causes water potential to decrease also.
*As solute is added, the water potential of a solution drops, and water will tend to move into the solution.

18. Molarity
Another way of expressing concentration, is called molarity. Molarity is the number of moles of solute dissolved in one liter of solution. The units, therefore are moles per liter, specifically it's moles of solute per liter of solution.

19. Be very careful to distinguish between moles and molarity.
moles of solute liter of solution
"Moles" measures the amount or quantity of material you have; "molarity" measures the concentration of that material.
So when you're given a problem or some information that says the concentration of the solution is 0.1 M that means that it has 0.1 mole for every liter of solution; it does not mean that it is 0.1 moles

20. What is the molarity of a solution made by dissolving 2
What is the molarity of a solution made by dissolving 2.5 g of NaCl in enough water to make 125 ml of solution?
molarity =
moles of solute
liter of solution
1 mole of any substance has a mass = to the atom’s atomic mass.
2.5 g NaCl x
1 mole NaCl
58.5 g NaCl
= mole
molarity =
mole NaCl        L =
0.34 M NaCl
Molarity is number of moles per Liters of solution

21. EXAMPLE PROBLEMS
1- An AP Biology student dissolves 98.4 g of FeSO4 in enough water to make L of solution. What is the molarity of the solution?
0.324 M
1 mole .
151.91g
x 98.4g = moles ÷ 2.00L= mol/L
151.91g

22. EXAMPLE PROBLEMS
Calculate the solute potential of a .1M NaCl solution at 22 degrees Celsius.
If the concentration of NaCl inside the plant cell is .15M, which way will the water flow if the cell is placed in the .1M solution?