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1. Water Potential Click

2. Water potential is a concept that helps to describe thetendency of water to move from one area to another, particularly into or out of cells. • Water molecules move randomly. • When water is enclosed by a membrane some of the moving water molecules will hit the membrane, exerting pressure on it. • This pressure is known as water potential.

3. It is measured in units of pressure, can be measured in kPa, MPa, bar. • Pure water has a water potential of zero. • A solution will have a lower concentration of water molecules so it will have a negative water potential.

4. Water Potential • We look at water movement in terms of water potential. (ψ) • Two factors: • Solute concentration and pressure • Pure water ψ =0 • The addition of solute lowers the water potential. (negative number) Water potential determines the rate and direction of osmosis.

5. ψp ψp • Pressure potential is important in plant cells because they are surrounded by a cell wall which, is strong and rigid. • When water enters a plant cell, its volume increases and the living part of the cell presses on the cell wall. • The cell wall gives very little and so pressure starts to build up inside the cell. • This has the tendency to stop more water entering the cell and also stops the cell from bursting. • When a plant cell is fully inflated with water, it is called turgid. • Pressure potential is called turgor pressure in plants) ψp ψp

7. Water moves from a place of high water potential to a place of low water potential. This is an open container, so the ψp = 0 This makes the ψ = ψs The ψs =-0.23, so ψ is -0.23MPa, and water moves into the solution.

10. Can a solution with a molarity of 0.2 be in equilibrium with a solution with a molarity of 0.4? • YES! • Pressure • Two solutions will be at equilibrium when the water potential is the same in both solutions. This does not mean that their solute concentrations must be the same, because in plant cells the pressure exerted by the rigid cell wall is a significant factor in determining the net movement of water.

11. Solute (osmotic) potential (ψs)= –iCRT 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?

12. The End of -iCRT

13. Let’s Take a class quiz!!

14. click So, we can now define osmosis as the movement of water molecules from a region of higher water potential to a region of lower water potential through a semi-permeable membrane.

15. Molarity

16. Be very careful to distinguish between moles and molarity. "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

17. What is the molarity of a solution made by dissolving 2.5 g of NaCl in enough water to make 125 ml of solution? 1 mole of any substance has a mass = to the atom’s atomic mass. Molarity is number of moles per Liters of solution

18. EXAMPLE PROBLEMS 1- An AP Biology student dissolves 98.4 g of FeSO4 in enough water to make 2.000 L of solution. What is the molarity of the solution? 0.324 M 1 mole . 151.91g x 98.4g = 0.647 moles ÷ 2.00L= 0.324 mol/L 151.91g Return to Water Potential Discussion