Water Potential Practice 10.9.14.docx - Name AP Biology...

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Name: AP Biology: Calculation of Water Potential (ψ) from Experimental Data The solute potential of sucrose solution can be calculated using the following formula: ψ S = -iCRT where i = ionization constant (for sucrose this is 1.0 because sucrose does not ionize in water; for NaCl, i = 2) C = Molar concentration (determined from your graph) R = Pressure Constant (R=0.0831 liter bars / mole ◦Kelvin) T = Temperature (◦Kelvin) (Calculate by 273 + ◦C of solution) Knowing the solute potential of the solution (ψ S ) and knowing the pressure potential of the solution is zero (ψ p = 0) allows you to calculate the water potential of the solution. The water potential will be equal to the solute potential of the solution.
Ψ = ψ p + ψ s 1. Water potential values are useful because they allow us to predict the direction of the flow of water. Suppose a student calculates the water potential of a solution inside a bag to be -6.25 bar s = -6.25, ψ p =0) and the water potential of a solution surrounding the bag is -3.25 bar (ψ p =0).

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