This laboratory experiment looks at the processes of diffusion and osmosis. It is important that you know what these terms mean. Review your class notes and check your textbook for definitions of the following terms. Remember that osmosis is a type of diffusion that examines the movement of water molecules. Diffusion and osmosis are affected by various parameters, including temperature, concentration, pressure and surface area.

Define the following terms in your own words. Remember to include scientific terms like solution, concentration, selectively permeable membrane, etc. when necessary.

Diffusion

Osmosis

Hypertonic

Hypotonic

Isotonic

This set of experiments will explore the effects of temperature and concentration on the rate of diffusion and osmosis. A selectively permeable membrane bag will be used to hold a solution of molasses. Molasses is a dark, thick, sticky, sweet solution that is produced during the process of refining table sugar. (It is used in cooking and baking; https://www.tasteofhome.com/recipes/giant-molasses-cookies/).

The selectively permeable membrane is a piece of dialysis tubing. The plastic film has minute pores that allow the passage of some molecules into or out of the bag. The dialysis tubing represents the cellular membrane that surrounds a cell. The cell membrane helps to regulate what enters and leaves the cell.

The bag containing molasses is incubated in a beaker of water. At various times, the bag is removed from the beaker of water and weighed. A change in the bag’s weight reflects gain or loss of substances inside the bag.

Dynamic equilibrium is reached when the number of molecules moving in one direction through the membrane is balanced by the number of molecules moving in the other direction through the membrane. At this point, there is still movement of molecules, but the solution concentration no longer is changing. Dynamic equilibrium may or may not be achieved in these experiments.

Part One: Diffusion and Osmosis – The Effect of Temperature

Read through the experiment. Construct a hypothesis about the relationship between temperature and the rates of diffusion and osmosis. Include all temperatures in your hypothesis statement(s).

Pre-soak three pieces of the dialysis tubing. Put the dialysis tubing in a beaker, add enough dH₂O to cover, and soak for five minutes.
The dialysis tubing is a porous membrane; it is permeable to water and molasses.
Remove the dialysis tubing from the water. Fold one end of the bag and secure it with a plastic clamp.
Using a pipette, fill each bag one third full with 100% molasses. Leave some empty space at the top of the bag, fold over the top, and secure it with another clamp. Rinse each bag and pat dry.
Using the electronic balance, weigh each bag and record the initial weight in grams (g) in Table 1.
One bag will be placed in a beaker of WARM WATER.

Label an empty beaker with your initials. Take this beaker to the water-bath. Scoop warm water out of the water-bath to fill the beaker half full, add the bag of molasses, and place the beaker on the rack in the water-bath. The bag should be completely covered by water. Close the lid on the water-bath.

A second bag will be placed in a beaker of ROOM TEMPERATURE WATER.

Using the flasks of room temperature water, fill a beaker half full, add the bag of molasses, and keep this beaker at your lab bench. The bag should be completely covered by water. Place a thermometer in the beaker, obtain the water temperature, and record the value in Table 1.

The third bag will be placed in a beaker of ICE WATER.

Put water and crushed ice in a beaker, add the bag of molasses, and keep this beaker at your lab bench. The bag should be completely covered by water. Place a thermometer in the beaker, obtain the water temperature, and record the value in Table 1. Be sure to replenish the ice throughout the experiment to keep the water cold and the temperature constant.

Using the diagram below, label the percentage of water and molasses concentrations inside and outside the dialysis bags at the beginning of the experiment.

Procedure continued:

After five minutes, remove each bag from its beaker, carefully pat dry, weigh, and record the results in Table 1. Record the actual values, do not round the numbers. Return each bag to its designated beaker for another 5 minutes, then remove the bag, pat dry, weigh, and record the data in Table 1. Repeat this process every five minutes for a total experimental time of 25 minutes.
The data for this experiment is located in the lab PowerPoint. Also examine the photographs of the experiment for use in the following questions. Transfer the data to Table 1 below. Then normalize the data by calculating the percent weight change (see calculation below) and put these calculated values in Table 2.
Identify two independent variables in this experiment: __________________________________
Identify the dependent variable in this experiment: __________________________________
At the beginning of the experiment, is the bag of molasses hypotonic, hypertonic, or isotonic to the solution in the beaker? (circle one)
Which way does the water move in this experiment? Name the transport process and explain in detail why the movement occurs.
Did the water turn yellow or brown in any of the beakers? If so, name the transport process and explain in detail why the movement occurs.
Use the data in Table 2: Diffusion & Osmosis – Effect of Temperature – Percent Weight Change to construct a line graph. Plot time on the x-axis and percent weight change on the y-axis. Whole and half numbers can be used when graphing the percent weight change data. For example, 10.2% can be plotted as 10%, 3.5% can be plotted as is, and 7.8% can be plotted as 8%. Plot all data points starting zero minutes through 25 minutes.
Examine the data in Table 2: Diffusion & Osmosis – Effect of Temperature – Percent Weight Change and the graph. Summarize the conclusions to this experiment in the space below or on a separate piece of paper. Restate your hypothesis and indicate if the results support or refute it. Explain the results and reference specific data in this summary to support your answer. Did any sample reach dynamic equilibrium? If the results did not support the hypothesis, identify possible reasons why.

Table 1: Diffusion & Osmosis – Effect of Temperature – Raw Data – Weight ( in grams (g))

Temperature (°C)	Initial Weight 0 minutes	Timed Weight 5 minutes	Timed Weight 10 minutes	Timed Weight 15 minutes	Timed Weight 20 minutes	Timed Weight 25 minutes	Water color at 25 min
Warm water (40°C)
Room temp water _____ °C
Ice water _____ °C

In order to interpret the results, you will need to compare the data. Because each bag contained a slightly different amount of molasses at the beginning, the data must be “normalized” to allow for valid comparisons. Calculate the Percent Weight Change using the following formula. Enter your numbers into Table 2.

Use the following equation to calculate the PERCENT WEIGHT CHANGE:

Timed weight – Initial weight x 100 = % weight change Initial weight

Table 2: Diffusion & Osmosis – Effect of Temperature – Percent Weight Change (in percent (%))

Temperature (°C)	Initial Weight 0 minutes	Timed Weight 5 minutes	Timed Weight 10 minutes	Timed Weight 15 minutes	Timed Weight 20 minutes	Timed Weight 25 minutes	Water color at 25 min
Warm water (40°C)	0
Room temp water _____ °C	0
Ice water _____ °C	0

Part Two: Diffusion and Osmosis – The Effect of Concentration

Read through the experiment. Construct a hypothesis about the relationship between concentration and the rate of diffusion and osmosis. Include all concentrations in your hypothesis statement(s).

Pre-soak three pieces of the dialysis tubing. Put the dialysis tubing in a beaker, add enough dH₂O to cover, and soak for five minutes.
Remove the dialysis tubing from the water. Fold one end of the bag and secure it with a plastic clamp.
Using a pipette, fill each bag one third full with molasses. Leave some empty space at the top of the bag, fold over the top, and secure it with another clamp. Rinse each bag and pat dry.
One bag will contain a 25% concentration of molasses.
A second bag will contain a 50% solution of molasses.
The third bag will contain a 100% solution of molasses.
Using the electronic balance, weigh each bag and record the initial weight in grams (g) in Table 1.
Each bag will be placed in a labeled, separate beaker containing in room temperature water. Place a thermometer in a beaker to obtain the water temperature and record the value in Table 3.

Using the diagram below, label the percentage of water and molasses concentrations inside and outside of each dialysis bag at the beginning of the experiment.

After five minutes, remove each bag from its beaker, carefully pat dry, weigh, and record the results in Table 1. Record the actual values, do not round the numbers. Return each bag to its designated beaker for another 5 minutes, then remove the bag, pat dry, weigh, and record the data in Table 1. Repeat this process every five minutes for a total experimental time of 25 minutes.
The data for this experiment is located in the lab PowerPoint. Also examine the photographs of the experiment for use in the following questions. Transfer the data to Table 3 below. Then normalize the data by calculating the percent weight change (see calculation below) and put these calculated values in Table 4.
Which way does the water move in this experiment? Name the transport process.
Did the water turn yellow or brown in any of the beakers? If so, name the transport process.
Identify two independent variables in this experiment: __________________________________
Identify the dependent variable in this experiment: __________________________________
Use the data in Table 4: Diffusion & Osmosis – Effect of Concentration – Percent Weight Change to construct a line graph. Plot time on the x-axis and percent weight change on the y-axis. Whole and half numbers can be used when graphing the percent weight change data. For example, 10.2% can be plotted as 10%, 3.5% can be plotted as is, and 7.8% can be plotted as 8%. Plot all data points starting zero minutes through 25 minutes.
Examine the data in Table 4: Diffusion & Osmosis – Effect of Concentration – Percent Weight Change and the graph. Summarize the conclusions to this experiment below or on a separate piece of paper. Restate your hypothesis and indicate if the results support or refute it. Explain the results and reference specific data in this summary to support your answer. Did any sample reach dynamic equilibrium? If the results did not support the hypothesis, identify possible reasons why.

Clean up:

At the sink under running water, remove the clamps on the molasses bags and empty the fluid from the bags into the sink. Discard the used dialysis bags. Rinse off the clamps and return to the tray. DO

NOT DISCARD THE CLAMPS.

Rinse and dry beakers.
Rinse out molasses pipettes.
Clean lab bench.

Table 3: Diffusion & Osmosis – Effect of Concentration – Raw Data – Weight ( in grams (g))

Temperature _______°C	Initial Weight 0 minutes	Timed Weight 5 minutes	Timed Weight 10 minutes	Timed Weight 15 minutes	Timed Weight 20 minutes	Timed Weight 25 minutes	Water color at 25 min
25% Molasses
50% Molasses
100% Molasses

Use the following equation to calculate the PERCENT WEIGHT CHANGE:

Timed weight – Initial weight x 100 = % weight change Initial weight

Table 4: Diffusion & Osmosis – Effect of Concentration – Percent Weight Change (in percent (%))

Temperature _______°C	Initial Weight 0 minutes	Timed Weight 5 minutes	Timed Weight 10 minutes	Timed Weight 15 minutes	Timed Weight 20 minutes	Timed Weight 25 minutes	Water color at 25 min
25% Molasses	0
50% Molasses	0
100% Molasses	0

Part Three: Microscopic Observation of Osmosis in a Plant Cell

Obtain one leaf from an aquatic plant, place it on a microscope slide with a drop of water and top with a cover slip. Examine the slide starting with low power, then moving to medium power and then to high power.
Plant cells are rectangular shaped. Chloroplasts and the cell wall are visible. The cell is filled with water, so the cell membrane is pressed up against the cell wall. A swollen cell is turgid. Sketch a picture of one plant cell and label the cell wall, cell membrane, and chloroplasts.
Next, remove the coverslip from the microscope slide, add a drop of 5% NaCl solution. Replace the coverslip and examine the slide under the microscope.

Is the 5% NaCl solution isotonic, hypertonic, or hypotonic to the cell? (circle one)

Will the cell remain the same size, gain water, or lose water? (circle one)

Will the cell wall size remain the same size, increase in size, or decrease in size? (circle one)

Sketch a picture of one plant cell and label the cell wall, cell membrane, and chloroplasts.


Plant cell + water	Plant cell + 5% NaCl solution

After the leaf was exposed to the 5% salt solution, what happened to the cell? Why did this occur?

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Effect of Temperature in Diffusion and Osmosis Lab Report

Table 1: Diffusion & Osmosis – Effect of Temperature – Raw Data – Weight ( in grams (g))

Table 2: Diffusion & Osmosis – Effect of Temperature – Percent Weight Change (in percent (%))

Table 4: Diffusion & Osmosis – Effect of Concentration – Percent Weight Change (in percent (%))