# Water Potential Problems HW.wanswers (2).pdf - Name Period...

• 4

This preview shows page 1 - 3 out of 4 pages.

Name: ______________________________________ Date: ________________ Period _______ Water Potential Problems Answers The solute potential (ψ S ) = – iCRT, where i is the ionization constant, C is the molar concentration, R is the pressure constant (R = 0.0831 liter bars/mole-K), and T is the temperature in K (273 + °C). Example 1 : A 0.15 M solution of sucrose at atmospheric pressure (ψ P = 0) and 25°C. S ) = – iCRT C= 0.15 M T= (273 +25) R= 0.0831 i= 1 (this is because sucrose doesn’t dissociate in water) ψ S = - (1)(0.15)(0.0831)(273+25) = -3.7 bars This example has an osmotic potential of -3.7 bars Ψ s + Ψ p = Ψ Ψ = 0 + -3.7 bars = -3.7 bars Example 2 : A 0.15 M NaCl solution contains 2 ions, Na + and Cl - ; therefore i = 2. Room Temperature of 25°C. S ) = – iCRT i=2 C= 0.15 M R= 0.0831 T= (273 +25) S )= -(2)(0.15)(0.0831)(298) = -7.4 bars Next: Ψ = 0 + -7.4 bars =-7.4 bars Careful when answering these questions: Which of the above has MORE water potential? Example 1
Which of the above is MORE concentrated? 1. If a cell’s Ψ = 3 bars and its Ψ = -4.5 bars, what is the resulting Ψ?
P S
2. The cell from question #1 is placed in a beaker of sugar water with Ψ S = -4.0 bars. In which direction will the net flow of water be?
• • • 