Calculation of Water Potential from Experimental Data
The solute potential of this sucrose solution can be calculated using the following formula:
i = Ionization constant
(for sucrose this is 1.0 because sucrose does not ionize in water)
C = Molar concentration
(determined from your graph – see your potato data)
R = Pressure Constant
(R = 0.0831 liter bars/mole
T = Temperature
K) (273 +
C of solution)
The units of measure will cancel as in the following example:
A 1.0 M sugar solution at 22
C under standard atmospheric conditions
= -i X C X R X T
= -(1)(1.0 mole/liter)(0.0831 liter bar/mole K)(295 K)
= -24.51 bars
Knowing the solute potential of the solution (ψ
) and knowing the pressure potential of the solution is zero
= 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 = 0 + ψ
The water potential of the solution at equilibrium will be equal to the water potential of the potato cells.