Name:
Period:
Date:
Diffusion & Osmosis Lab
Purpose: To observe and measure the processes of both diffusion and osmosis.
Part A: Cornstarch & Iodine – In this lab you will observe the diffusion of a substance across a semi permeable membrane. Iodine is a known indicator for starch. An indicator is a substance that changes color in the presence of the substance it indicates.
Procedure:
1. Fill a plastic baggie with a teaspoon of cornstarch and half a cup of water and tie the bag.
2. Fill a beaker halfway with water and add ten drops of iodine.
3. Place the baggie in the cup so that the cornstarch mixture is submerged in the iodine water mixture.
4. Wait fifteen minutes and record your observations in the data table.
5. While you are waiting, answer the following questions.
Questions:
a) Define diffusion:
b) Define osmosis:
c) What is the main difference between osmosis and diffusion?
d) Why is iodine called an indicator?
e) Molecules tend to move from areas of ______concentration to areas of ______concentration.
f) Is the baggie or beaker more concentrated in starch?
g) Is the baggie or beaker more concentrated in iodine?
h) Iodine solution – is the baggie or beaker hypotonic?
i) Starch solution – is the baggie or beaker hypertonic?
j) Which one is hypotonic in relation to starch, the baggie or the beaker?
k) If the baggie was permeable to starch, which way would the starch move, into the bag or out of the bag?
l) If the baggie was permeable to iodine, which way would the iodine move, into or out of the bag?
m) If the baggie was permeable to iodine, what color would you expect the solution in the baggie to turn?
n) What about the solution in the beaker?
o) If the baggie was permeable to starch, what color would you expect the solution in the baggie to turn?
p) What about the solution in the beaker?
Data Table
Starting Color / Color after 15 minutesSolution in Beaker
Solution in Bag
Post Lab Report:
1. Based on your observations, which substance moved, the iodine or the starch?
2. How did you determine this?
3. The plastic baggie was permeable to which substance?
4. Is the plastic baggie selectively permeable?
5. Sketch the cup and baggie in the space below. Use arrows to illustrate how diffusion occurred in this lab.
Part B – Potato Lab: In this lab you will determine the molarity of a potato. **Molarity is a measure of how concentrated a solution is. A 1 Molar sugar solution has 6.022 X 1023 molecules of sugar. A 2 M solution would have twice that. A potato will have between 0 and 1 M – use this to make a hypothesis.
Procedure:
1. Label 6 beakers 0M, .2M, .4M, .6M, .8M, and 1.0M respectively.
2. Find the mass of four slices of potato (dry) in grams. Record the mass (initial mass) and place the slices in the beaker labeled 0M.
3. Repeat until each beaker has four potato slices (which you have massed and recorded).
4. Add enough of each solution (to the properly labeled beakers) until the potato slices are covered completely. Let sit for 30 minutes.
5. Remove the slices, blot dry, and mass each set of four, again recording results (final mass).
6. Find the percent weight gain of the potatoes for each solution:
Final Mass – Initial Mass X 100%
Initial Mass
7. Make a line graph of your results:
Independent variable (x-axis) = Molarity of each solution (0to1.0M)
Dependent variable (y-axis) = % weight gain
8. Where the line crosses the zero point on your graph is the molarity of the potato.
Data Table
0M / .2M / .4M / .6M / .8M / 1.0MInitial potato weight
Final potato weight
% weight gain
Draw a line graph below based on the information in your data table: