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Potato in Solutions Activity (mass)

Questions:

  1. What is the mass change of a potato cube in fresh water?
  2. What is the mass change of a potato cube in salt water?

Hypotheses (predictions):

(Record your predictions on your paper. Note there are two questions so there will be two predictions). (4 pts)

Equipment:

(2) potato cubes (2) small beakers (1) balance
tape, marker & ruler fresh water table salt graduated cylinder

Procedure:

  1. Make 25 ml of a 3% salt water solution. Show your calculations for the amount of NaCl needed. (2 pts)
  2. Carefully cut two potato cubes. Each cube should be about 3cm³ .
  3. Gently flip the cubes around on a paper towel to remove excess surface moisture.
  4. Mass the potato cubes. Each cube will likely be different.
  5. Place a potato cube in each of the beakers.
  6. Nearly fill the first beaker with fresh water. Label the beaker.
  7. Nearly fill the second beaker with 3% salt solution. Label the beaker.
  8. Set aside the beakers as directed by your instructor.
  9. The next day, gently flip the cubes around on a paper towel to remove excess surface moisture and mass the potato cubes.

Data Section:

  1. Record the before and after mass of each cube. (4 pts)
  2. Record your calculations for the percentage change for each mass. (4 pts) Use this formula:

    [(after mass - before mass) / before mass]* 100

  3. Use graph paper to graph the solution concentration (x-axis) vs. percentage potato cube mass change. (4 pts)

Analysis:

Answer these analysis questions in complete sentences.

  1. For each solution did the potato cube mass increase, decrease or stay the same? (2 pts)
  2. Why would the potato cube change mass? (2 pts)
  3. Make a before sketch of a typical plant cell and two after sketches: one for the fresh water cube and one for the salt water cube. (6 pts)
  4. Describe the two solutions in terms of being hypotonic, hypertonic and isotonic solutions. (2 pts)
  5. Looking at your graph, estimate what salt concentration would be an isotonic solution for the potato cube? Explain your reasoning. Hint: what would a 0% mass change mean? (4 pts)