I'm doing a potato lab in my AP Bio class and am confused on how to calculate the water potential of the potato cell.
The equation to calculate for water potential is Ψ = 0 + Ψ
s. Ψ
s is the solute potential and the equation for Ψ
s = -i x C x R x T
i = ionization constant (we're using sucrose in the lab, it has 1.0 ionization constant)
C = Molar concentration (this is where I am really confused)
R = pressure constant (we were given this info, it's R=0.0831 liter bars/mole K)
T = temperature K (273 + C) (C = 22)
so far, this is what i have Ψ = -(1)(?)(0.0831)(295)
So I really need help on finding the molar concentration.
Here are the directions to the lab:
Designing and Conducting Your Investigation Materials
• Potatoes (varied types) cut in cubes
• Balances
• Metric rulers
• Cups
• Color-coded sucrose solutions of different, but unlabeled, concentrations prepared by your teacher
Step 4 You will be assigned one type of potato to test, record the type of potato.
Step 5 Label 5 cups: 0M, 0.4M, 0.8M, 1.0M, and Unknown (followed by the letter of your unknown solution) include your lab group name on each cup. Record your unknown letter.
Step 6 Obtain 4 cubes of your assigned potato for each cup (20 cubes total) and determine the mass of four cubes together for each cup and record the mass in a data table below.
Step 7 Fill each cup with 20 ml of the appropriate solution and place your cups somewhere in the classroom that is safely away from student work areas. Let them stand overnight.
Step 8 Remove the cubes after approximately 24 hours and blot them gently on a paper towel, then determine each cups total mass and record the mass in the data table below.
Step 9 Calculate the mass difference and the percent change in mass for each cup and record it below.
Step 10 Collect class data as percent change in mass, for each of the types of potatoes at the four different molarities and record it in a data table below.
Step 12 Graph both your individual data and the class average for the percent change in mass on the attached graph paper. Plot your unknown as a single point and clearly label it on your graph