Osmosis Lab
Introduction
Solutions consist of solutes (particles) dissolved in a solvent (liquid). In all living organisms there are many different
types of solutes including salts and sugars. The major solvent is water. There are different concentrations of solutes in
various regions of an organism, including differences between the inside and the outside of the cell.
Living organisms tend towards being in balance, or in equilibrium, with their environment. Cells achieve this through
diffusion. Diffusion is the random movement of solutes from an area of higher concentration to an area of lower
concentration. Osmosis is a special case of diffusion. Osmosis is the movement of water through a selectively permeable
membrane. During osmosis, water molecules diffuse through the membrane from a region of higher water potential to a
region of lower water potential until equilibrium is reached.
Objective:
Study and understand the process of osmosis.
Materials: Potato, Sucrose Solution, Balance Scale, Pipette, Paper Towels, Plastic Cups
Experiment: Osmosis Lab
Prepare a stock solution of 1.0 M sucrose. Use the following table to prepare the remaining solutions. Complete the
following steps for each sucrose solution:
Table 1: Solute and solvent amounts for different sucrose solutions
Sucrose solution
1.0 M Sucrose solution
Distilled H2O
1.0 M
60 ml
0 ml
0.8 M
48 ml
12 ml
0.6 M
36 ml
24 ml
0.4 M
24 ml
36 ml
0.2 M
12 ml
48 ml
0.0 M
0 ml
60 l
1. Pour approximately 60 ml of one sucrose solution into a labeled plastic cup.
2. Use a scalpel or plastic knife to cut five potato slices for each test solution. Cut each slice to approximately 2 cm in
length. Do not include any skin on the slices.
3. Calculate the total mass for the five slices and record as the initial mass in your lab notebook. Put the five slices into
one of the labeled cups containing a sucrose solution.
4. Repeat steps 3 – 5 for the other sucrose solutions.
5. After each set of potato slices has soaked for 25-30 minutes, remove the slices from the cup and blot them gently on a
paper towel.
6. Record the final mass and calculate percent change in mass.
Results:
 Complete a properly constructed raw data table for each experiment. The table for Experiment 2 should look like
Table 2 (record ONLY numbers, NO units).
Table 2: Mass (g) of potato slices at different sucrose concentrations (+/- 0.1g)
Sucrose
concentrations
Initial Mass
Final Mass
Change in Mass
% Change in
Mass
Average %
Change in
Mass
0.0 M sucrose
0.2 M sucrose
0.4 M sucrose
0.6 M sucrose
0.8 M sucrose
1.0 M sucrose
Calculate the following:
a. calculate the percent change in mass of each potato slice.
(Final mass) – (Initial Mass) x 100 = percent change in mass
Initial Mass
b. calculate the average change in mass:
(%change1 + %change2 + %change3 + %change4 + %change 5) = average percent change in mass
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Processed Data: (we will do this in the computer lab)
For this investigation you are required to write a full report with a date and title, introduction, hypothesis, variables,
materials, methods, data collection, data processing, conclusion and evaluation. (Note: This lab will be marked against
IB criteria.) The lab report must be TYPED and put into a binder to be kept in the classroom.
Lab Report Procedure:
1. Introduction - Aim: A sentence stating the purpose of the lab or what the scientist wants to accomplish in the
lab)  Example Aim: To observe the osmotic effect of different sucrose concentrations on potatoes
A. Title
B. Research Question
C. Background Information
2. Hypothesis - A hypothesis is an educated guess about how things work. A hypothesis can usually be written as
an ‘If______ Then______’ statement. A hypothesis should be something that you can actually test - called
a testable hypothesis. In other words, you need to be able to measure both "what you do" and "what will
happen.")
o Example Hypothesis: If the concentration of sucrose increases, then the mass of the potato will
decrease. However, if the concentration of the solution in the beaker is less than that of the
potato (such as distilled water), then the mass of the potato will increase.
3. Variables - (A variable is a factor that can influence the outcome of an experiment or factors that can affect a
tests outcome. Experiments usually have three variables: dependent, independent and controlled)
A. Dependent - the dependent variable is the response that is measured. It is what the investigator thinks
will be affected during the experiment.
B. Independent - the independent variable is the variable that is varied or manipulated by the researcher.
It is what the investigator thinks will affect the dependent variable
C. Control – The control of an experiment is the variable, which you keep constant. Since the investigator
wants to study the effect of one particular independent variable, the possibility that other factors are
affecting the outcome must be eliminated
4. Control of Variables - This is not the same as “the control” above! All the aspects of the experiment that must
be kept constant to ensure that the tests/experiment is valid. There will be several of these not just one! You
must be thorough and think of as many controlled variables as you can. That said, don’t include controlled
variables that aren’t significant. For example if you’re measuring the growth of yeast then the temperature
definitely needs to be controlled (assuming temperature is not your independent variable) but the same location
is not going to be a significant factor. Your must explicitly indicate how each controlled variable identified in
your variables section was controlled. If you can’t actively control a variable then your method should include a
means of monitoring it.
5. Materials (list all the materials that were used)
6. Method - (A step-by-step process; can be replicated exactly by other scientists. The procedure may be a list but
in complete sentences)
1. Label six beakers with six different concentrations of sucrose solutions (1.0 M sucrose, 0.2 M sucrose,
etc.)
2. Fill the six beakers with the correct amount of sucrose solution previously labeled.
3. With the scalpel/plastic knife, cut five slices of potato.
4. Cut the ends of the potato cylinders, making them even on the edges and remove the skin.
5. Weigh the potato cylinders on an electronic balance and record their initial (pre-immersion) masses in a
data table.
6. Insert five potato slices into each labeled beaker. (There should be five potato slices per beaker)
7. Record the date and time of potato slice immersion.
8. Leave the potatoes in the beakers for 30 minutes.
9. After 30 minutes, take out all potato slices and record date and time of extraction.
10. Blot the potatoes with paper towel removing excess water.
11. Weigh the potato slices on an electronic balance and record their final (post-immersion) mass in a data
table.
12. Calculate the average percent change in mass and length of the potato cylinders.
7. Data Collection - (A record of raw data – includes tables, annotated drawings, & observations. Raw data is actual
data measured)
A. Record raw data in a table. (Use appropriate significant figures, units, and levels of uncertainty for
quantitative reading)
B. Record observations. (You can make a note of observations pre- and post- potato immersion)
8. Data Processing - (Includes the presentation of raw data graphically or as a table, and calculations of change,
proportion, percentage or other statistical value if needed)  these come from the calculations from the lab
A. Record your calculated data in a data table.
B. Graph the average percent change for both mass using Microsoft Excel.
9. Conclusion - (Describe your results in written form)
A. State a conclusion based on the findings (analyze your processed data and draw a conclusion).
B. Justify/explain your conclusion with a reasonable interpretation of the data. (What do the results show?
Are there any trends? What can you interpret from the results? Relate your comments back to
processed data tables and graphs)
C. Justify your conclusion and findings using appropriate literature. (Is your conclusion right? Is your
conclusion wrong? Can you explain any unexpected results? Compare your experimental results with
textbook or literature values. The literature consulted should be fully referenced.)
10. Evaluation - (Evaluate/assess your experiment)
A. Evaluate the method, errors, limitations, and weaknesses. (What are the sources of error in my method,
manipulation, and/or analysis? Comments about the precision and accuracy of the measurements are
relevant here. When evaluating the procedure used, specifically look at the processes, use of equipment
and management of time.)
B. Suggest realistic improvements in respect of identified weaknesses and limitations (suggestions should be
based on the weaknesses and limitations identified in aspect 2. Address modifications to experimental
techniques and data range. Modifications should be realistic and clear - ex. do not state generally that
more precise equipment needs to be used – you must be more specific)