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Sheet1
Lab 4 Data
Solution
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Trial 6
Isosmotic Threshold (M)
Sucrose
NaCl
0.6
0.25
0.55
0.35
0.55
0.3
0.50
0.30
0.50
0.30
0.60
0.35
CaCl2
0.20
0.25
0.15
0.20
0.25
0.20
Electrical conductivity (EC) in µS
Conc (M)
Sucrose
NaCl
CaCl2
0.05
15
4500
8550
0.1
22
10950
19500
0.15
23
18400
29400
0.2
25.5
23500
37650
0.25
26
28800
47500
0.3
27.5
38400
54950
0.35
28
43500
63500
0.4
29
49300
71750
0.45
29.5
57300
83950
0.5
30
63500
91900
Page 1
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Page 2
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Page 3
LAB 4 Assignment: Osmotic Potential
Worth: 4% (marked out of 40)
Due: March 14th, 2023
Data Analysis (15.5 marks)
1. Prepare a solution that is 20ml (volume) and 3M NaCl. The molecular weight of
NaCl is 58.44 g/mol. Use the formulae found on page 32 of your lab manual and
list the following (do not forget to include your formulae and units): (3 marks)
a. How much NaCl must you add to your flask to prepare this solution? Show
your calculation.
b. Would you add 20ml of water to the salt in your flask? Why or why not?
c. How many ml of water would you need to dilute your 3M NaCl solution to
0.5M if you want 5ml of the new solution? Show your calculation.
2. Create a properly formatted table which includes: (6 marks)
a. The solute (sucrose, NaCl, CaCl2) (column 1)
b. The average isosmotic threshold for each solute
i. Use the data from Part III on Nexus
ii. No standard deviations required
c. The osmotic coefficient (ϕ) for each solute
i. Use the following values: sucrose = 1.02, NaCl = 0.93, CaCl 2 = 0.86
d. The # ions/molecule (V) for each solute
i. How many ions does the solute dissociate into?
e. The osmotic potential (ΨO) for each solute
i. Calculated using the formula on page 34 in the lab manual
ii. Include a sample calculation for one of the solutes below your table
3. Using the values from your table from data analysis 2, what is the osmotic
potential of the red onion cell? Show your work. (1 mark)
4. Convert the electrical conductivity data on Nexus (obtained the same way as part
IV in the lab manual) to osmotic potentials. This is done by multiplying the
recorded meter values by the conversion constant provided to you in the tutorial.
Create a graph of osmotic potential versus concentration of the solutions where
all three solutions (sucrose, NaCl, and CaCl2) appear on the same graph. Your
figure should be properly formatted with an associated legend. A best-fit straight
line must be included for each solution. (4 marks)
5. Use your answer from data analysis 3 as your y-value and the line equations
from data analysis 4 to determine the concentration of each solution which would
be isotonic to the cell. Show your work including the original formulae! (1.5
marks)
Questions (24.5 marks)
Note: for some of these questions, you may have to do a bit of research! In these cases,
in-text citations and final references are not required (for this assignment only).
1. Create a computer generated diagram of a plant cell in a hypertonic, hypotonic,
and isotonic solution. Indicate the movement of water by osmosis over the cell
membrane. Do not forget to include a figure caption. (4.5 marks)
2. How do plant cells and animal cells differ when it comes to changes in the
tonicity of solutions surrounding them? Use the example of a red blood cell and a
red onion cell to make this comparison. (2 marks)
3. Why does deplasmolysis of the cell occur over time? Why might this differ
between cell types? (2.5 marks)
4. List three features of red onion epidermis makes it highly useful for observing
osmosis under bright field microscopy? (1.5 marks)
5. Why is osmotic potential always a negative number? (1 mark)
6. When determining the osmotic potential of a cell, you are required to take an
average of the osmotic potential for each solution. Why is this necessary?
Include a brief description of the formula for osmotic potential. (2 marks)
7. Identify the chemical nature (electrolyte or non-electrolyte) of each of your three
solutions. How many ions will each molecule dissociate into? (2 marks)
8. Assuming you had determined an isosmotic threshold of 0.8M for CaCl 2, what
would you expect the isosmotic threshold to be for KCl? Provide a specific
concentration by showing your thinking and add a written explanation. (2 mark)
9. Why do electrolytes require a decreased concentration of solutes in order to
reach the isosmotic threshold? Why are these concentrations not the same for all
electrolytes (Hint: there are two reasons that are directly addressed on page 31
of your lab manual). (3 marks)
10. Explain why the electrical conductivity method of determining the isosmotic
threshold cannot be used for all solutions. (1 mark)
11. Explain the concept of osmotic potential as it relates to cell volume regulation in
plants. Include one cool example of how cells maintain osmotic balance in harsh
environments (each with a 1 sentence explanation). You will need to include a
single in-text citation and reference for this question. (3 marks)
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