OSMOSIS WITH GUMMY BEARS
Purpose
To investigate the movement of water into and out of a polymer (such as a gummy bear).
Experimental Question
Will soaking Gummy Bears in distilled water or salt water affect the size and/or mass of a gummy bear?
Hypothesis: ______
______
Materials (per group)
o 2 Gummy Bears
o 2 plastic cups
o Distilled water
o Centimeter ruler
o Salt
o Scale
o Permanent marker
Procedure
1. Obtain two plastic cups and two different color gummy bears.
2. On the side of each cup, write your name and your partners name using a permanent marker. Mark one cup for salt water and the other for distilled water.
3. Find the mass of each bear using a balance. Record the data in the data table.
4. Measure your bears from top to bottom (length), from side to side (width) and from front to back (depth). Use your measurements to calculate the volume of your gummy bear. Record your data in the data table.
5. For better accuracy, calculate the volume using the water displacement technique. Fill a graduated cylinder with about 20 mL of water. Add the gummy bear, and measure the new volume. The difference between the original volume and the new volume is the bear’s volume.
6. Place 1 bear in the cup labeled “distilled.” Add just enough distilled water to the cup to fully cover the bear.
7. Pour roughly the same amount of water in the cup marked “salt.” Before adding the bear, add table salt in small amounts until it no longer completely dissolves when stirred. This is a saturated solution. Now add the gummy bear.
8. Place the cups on the counter, and let them soak until the next class period.
9. On the next lab day, gently pour the water from each cup into the sink.
10. Measure the height, width, and depth of each gummy bear. Calculate the volume. Record your data.
11. Place the bear in a graduated cylinder of water and calculate the volume displacement.
12. Find the mass of each bear. Record in the data table.
Data Table for Mass
Gummy Bear 1 (color: ______) Gummy Bear 2 (color: ______)
Day 1Salt Water / Day 2
Salt Water / Day 1
Distilled Water / Day 2
Distilled Water
Mass of gummy bear
(grams)
Data Table for Volume
Gummy Bear 1 (color: ______) Gummy Bear 2 (color: ______)
Day 1Salt Water / Day 2
Salt Water / Day 1
Distilled Water / Day 2
Distilled Water
Volume of gummy bear
(cm3)
Volume of gummy bear
(mL)
Conclusions
1. What happened to the bears when placed in distilled water? Why?
2. What happened to the bears when placed in salt water? Why?
3. What do you think would have happened to the bears if, after the last day, they were again placed in distilled water?
4. Was there a difference in your results using tap water compared to distilled water? If so, why?
5. Was the distilled water hypotonic or hypertonic? As a result, what happened to the bear?
6. Was the salt water hypertonic or hypotonic? As a result, what happened to the cell?
7. Compare the volumes found by measuring the bear, versus that found using water displacement. Were they similar? Which do you think is more accurate? Explain.
8. Calculate the percent change in volume after each step of the experiment.
a. % change in volume = (final volume - initial volume)/ initial volume x 100
b. Place the percentages in the table below:
Bears / % Change in Water / % Change in Salt WaterTap Water Bear
Distilled Water Bear
9. Make a bar graph of the percent changes.
a. Provide a title, and label the axes.
b. Place the data for both bears on the same graph.
c. If you have a negative value for a percent change, start the vertical axis at a negative number. (For example: -50, -25, 0, 25, 50, 75, 100, etc.)