Potato Lab

Change in mass calculation:

Individual data – Change in mass of potato cores

Sucrose Molarity / Initial mass / Final mass / % Change in mass
0
0.2
0.4
0.6
0.8
1.0

Class data – Average Change in mass of potato cores

% Change in mass
Sucrose Molarity / Group 1 / Group 2 / Group 3 / Group 4 / Group 5 / Group 6 / Average
0
0.2
0.4
0.6
0.8
1.0

There may be more or less groups in the above chart than there really are in class…you guys know to ignore blank columns or squish in extra columns if you need them…right?

Graph your data…that is, graph the percent change in mass for your individual group and then for the class average. You’ll want to do something you guys almost never do…give your graph a title. (Hint: “Graph” is not a good title) (Additional hint: “Averages” or “Individual and class data” or “Percent change” are also not good titles)

You will also need to resist the almost overwhelming urge to connect the dots. Draw a best fit line for the CLASS AVERAGE DATA. Draw a different best fit line in a much lighter color or use a dashed line for individual data.

%
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s /
Sucrose molarity

Where does the class average cross X=0 (x-intercept)? ______M

That is the molarity at which a potato would neither gain nor lose mass.

Test that out. Mix a solution that has that molarity.

Formula for mixing solutions:

M1V1 = M2V2

Weigh 4 potatoes before placing them in the solution and then someone else will weigh them after. We don’t expect to see any change in mass. List some reasons why we still might see a change in mass:

Calculating Water Potential

Water potential is the measure of the relative tendency of water to move from one area to another, and is commonly represented by the Greek letter Ψ (Psi).

Another way to look at it is that water potential is a measurement of the potential (tendency) of water to leave one place and go to another.

Water potential is affected by two things: pressure and solutes.

(direct) (indirect)

More pressure= higher water potentialMore solutes=lower water potential

How do you calculate water potential?

This formula:
Solute potential = –iCRT
i = The number of particles the molecule will make in water; for NaCl this would be 2; for sucrose or glucose, this number is 1
C = Molar concentration (from your experimental data)
R = Pressure constant = 0.0831 liter bar/mole K
T = Temperature in degrees Kelvin = 273 + °C of solution

Assuming it was 23oC in the room, what is the water potential of the potatoes?

Now, you are given a sweet potato, 2M solution, cups, graduated cylinders, scales, distilled water. Calculate the water potential for a sweet potato.

Rubric for potato lab:

Introduction

Background:

Purpose

Hypothesis

My signature: ______

Materials and Experiment

Materials

Procedure

My signature ______

Data

Table

Graph – include a line of best fit to calculate sucrose molarity?

Conclusion

Analysis question

  1. When you calculated the russet potato molarity and tested it out, what did you find? What might be the reason for any difference between the calculated molarity and the actual molarity?
  2. When you calculated the sweet potato molarity, how did you correct for some of the error in the russet molarity?
  3. Looking at the sucrose molarity of russet and sweet potatoes, how do they compare?
  4. What are 3 things you have to keep constant in this lab?
  5. How did you meet the need of multiple trials in the sweet potato portion of this lab?
  6. What is the water potential (show all calculations) for a sweet potato?
  7. Given the following data for zucchini cores, what is the water potential for zucchini? (attach a graph and show all calculations)

% change in mass / sucrose molarity
20 / 0.0
10 / 0.2
-3 / 0.4
-17 / 0.6
-25 / 0.8
-30 / 1.0