Potato Cores Lab
BIOLOGY OSMOSIS LAB REPORT
1. Research Question/ Aim
How do the different sodium chloride concentrations of solutions affect the length (measured in mm) and mass (measured in grams) of potato cores placed in them overnight (approximately 10 hours)?
2. Hypothesis
Alternative hypothesis: As the concentration of sodium chloride in the solution increases, the mass of the potato cores will decrease. If the solution they are in has a lower water potential than the potato cores, there will be net movement of water out of the potato cores. If the solution has a higher water potential than the potato cores, there will be net movement of water into the potato pieces. Therefore, potato cores in less concentrated solutions will gain more weight …show more content…
than the potato cores in more concentrated solutions.
Null hypothesis: Different sodium chloride concentrations in solutions have no effects on the mass of the potato cores.
3. Analysis of Variables
Type of Variable
Details
Notes on how variable is manipulated / measured / controlled
Independent (manipulated)
Sodium concentration of the solutions
Different amount of salt (sodium chloride) is put in the solvent (water) to make 0.34M, 0.67M, 1M, 1.34M, 1.67M solutions.
Dependent (responding)
Final mass of potato pieces
Measured at the end of the experiment with a ruler (in mm) and an electronic balance (in gram).
Controlled variables
Volume of solutions
Each solution is mixed with 300 cm3 of solvent (water) and then divided into two beakers with 150 cm3 in each.
Room temperature
All beakers are kept in the same room, so that they all experience the same conditions.
Type of potato
All the potato pieces come from potatoes bought at a store, packaged together.
Initial sizes of potato pieces
Measured before putting the pieces into the solutions with a ruler (in mm) and an electronic balance (in gram).
Temperature of the solutions
All the beakers were kept in the same place, so the solutions experienced the same conditions.
Size and material of the beakers
The 500 ml beakers were made of glass.
Duration of time the potato is left in the solutions
The potato pieces were left in the solutions overnight, approximately 10 hours.
4. Background …show more content…
Information
Osmosis can be defined as the movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration.
The semi-permeable membrane allows small particles through it but does not allow large particles such as sodium chloride. Osmosis will continue until a state of equilibrium is reached i.e. there is no area with a higher or lower concentration than another area.
To land plants, water and osmosis are vital as they play leading roles in the structural support of a plant, they facilitate transport of materials, etc. Lack of water will lead to a plant wilting and possibly dying.
When a cell is in a hypotonic solution (more solute concentration than the cell), water will move from the hypertonic solution (less concentrated) to the hypotonic solution via the process of osmosis.
In this experiment, the movement of water in and out of potato cells left in sodium chloride solution will be investigated. The sodium chloride molecule is too large to be passively transported across the cell membrane, so only net movement of water will happen without any input of energy.
5. Apparatus/Materials
2 x potatoes
1 x bag of salt (sodium chloride)
10 x 500 ml glass
beakers
1500 cm3 of water
500 ml measuring cylinders
30 cm plastic ruler
Electronic balance
Knife
Cutting board
Tweezers
Stirring rod
6. Method/Methodology/Procedure
A. Preparation of solutions
1. The molar mass of sodium chloride is 58.44 g/mol.
Molar concentration = moles of solute/ volume of solution in liters
1M sodium chloride solution = 58.44g sodium chloride in 1 liter of water.
0.34M sodium chloride solution = 19.87g sodium chloride in 1 liter of water
= 5.96g sodium chloride in 300 cm3 of water
Molar concentration
Sodium chloride (g)
Water (cm3)
0.34M
5.96
300
0.67M
11.74
300
1M
17.53
300
1.34M
23.49
300
1.67M
29.28
300
2. Mix the solutions and then divide each solution into two 500 ml glass beakers, each containing 150 cm3 of solution.
3. Label the beakers with the concentration of each solution. There are two beakers for each concentration of sodium chloride.
B. Preparation of the potato cores
1. Wash and dry the potatoes. Peel the potatoes.
2. Cut the potatoes into pieces of equal lengths using a sharp knife. The pieces should be rectangular cuboid. Be as precise as possible. Prepare 50 pieces (10 for each solution).
3. Using a ruler and an electronic balance, measure the length (in millimeters) and mass (in grams) of each potato pieces. Record these initial measurements.
4. Using tweezers, carefully place the 5 potato pieces into each beakers and mark their positions. Avoid moving the beakers too much.
5. Put the beakers away in an undisturbed place. The potato pieces can be put into the beakers at the place where they will be left overnight in order to avoid shifting the potato pieces.
7. Data Collection
Table 1: The initial and final lengths (mm) and masses (g) of potato pieces put in 0.34M sodium chloride solution for 10 hours
Molar concentration: 0.34M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
41
45
+4
2.91
3.32
+0.41
B
40
45
+5
2.94
3.22
+0.28
C
41
43
+2
2.32
2.58
+0.26
D
42
45
+3
3.02
3.37
+0.35
E
41
41
0
2.34
2.55
+0.21
F
40
41
+1
2.56
2.88
+0.32
G
41
41
0
2.63
2.98
+0.35
H
42
44
+2
3.48
3.91
+0.43
I
40
44
+4
3.08
3.39
+0.31
J
41
45
+4
2.86
3.27
+0.41
Table 2: The initial and final lengths (mm) and masses (g) of potato pieces put in 0.67M sodium chloride solution for 10 hours
Molar concentration: 0.67M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
36
37
+1
1.28
1.35
+0.07
B
37
39
+2
2.50
2.64
+0.14
C
37
39
+2
1.59
1.67
+0.08
D
37
38
+1
1.80
1.89
+0.09
E
39
40
+1
1.74
1.86
+0.12
F
39
42
+3
1.85
1.98
+0.13
G
39
41
+2
1.39
1.52
+0.13
H
37
40
+3
1.96
2.09
+0.13
I
37
40
+3
1.99
2.13
+0.14
J
38
41
+3
2.59
2.76
+0.17
Table 3: The initial and final lengths (mm) and masses (g) of potato pieces put in 1.0M sodium chloride solution for 10 hours
Molar concentration: 1.0M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
42
42
0
1.77
1.85
+0.08
B
44
44
0
2.13
2.20
+0.07
C
44
43
-1
2.67
2.77
+0.10
D
43
44
+1
2.03
2.11
+0.08
E
42
43
+1
2.26
2.34
+0.08
F
42
43
+1
2.38
2.45
+0.07
G
42
43
+1
2.05
2.14
+0.09
H
40
42
+2
1.94
2.01
+0.07
I
40
40
0
1.17
1.20
+0.03
J
40
42
+2
1.29
1.35
+0.06
Table 4: The initial and final lengths (mm) and masses (g) of potato pieces put in 1.34M sodium chloride solution for 10 hours
Molar concentration: 1.34M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
41
41
0
2.83
2.90
+0.07
B
40
40
0
2.75
2.80
+0.05
C
41
40
-1
2.25
2.25
0
D
41
40
-1
2.51
2.52
+0.01
E
40
41
+1
2.44
2.42
-0.02
F
39
40
+1
2.40
2.38
-0.02
G
38
39
+1
2.73
2.73
0
H
37
39
+2
2.31
2.33
+0.02
I
37
37
0
1.79
1.80
+0.01
J
38
37
-1
2.34
2.40
+0.06
Table 5: The initial and final lengths (mm) and masses (g) of potato pieces put in 1.67M sodium chloride solution for 10 hours
Molar concentration: 1.67M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
39
40
+1
3.31
3.40
+0.09
B
42
42
0
3.06
3.10
+0.04
C
41
42
+1
2.68
2.71
+0.03
D
40
41
+1
3.14
3.21
+0.07
E
41
41
0
2.74
2.80
+0.06
F
41
42
+1
2.26
2.29
+0.03
G
40
40
0
1.91
1.96
+0.05
H
40
41
+1
2.19
2.25
+0.06
I
42
44
+2
2.75
2.82
+0.07
J
42
40
-2
3.18
3.30
+0.12
8. Data Processing and Analysis
A. Calculations
Average initial measurement = sum of all initial measurements/10
Average initial length of potato pieces put in 0.34M solution = (41+40+41+42+41+40+41+42+40+41)/10 = 40.9 (mm)
Percent of change = [(final measurement – initial measurement)/initial measurement] x 100
Percent of change in lengths of potato pieces put in 0.34M solution = average difference/average initial length x 100 = 6.11%
Table 6: Percent of changes in the lengths and masses of the potato pieces
Molar concentration
Average initial
Average difference
Percent of changes (%)
Length (mm)
Mass (g)
Length (mm)
Mass (g)
Length
Mass
0.34M
40.9
2.81
+2.5
+0.33
6.11
11.74
0.67M
37.6
1.87
+2.1
+0.12
5.58
6.15
1M
41.9
1.97
+0.7
+0.07
1.67
3.55
1.34M
39.2
2.43
+0.2
+0.02
0.51
0.82
1.67M
40.8
2.72
+0.5
+0.06
1.22
2.20
Table 7: Uncertainty of the volume of water
Volume of water added to the beakers (cm3)
Uncertainty of the measuring cylinder (cm3)
Percentage uncertainty
300
±1
±0.33%
300
±1
±0.33%
300
±1
±0.33%
300
±1
±0.33%
Percentage uncertainty = uncertainty of the measuring cylinder/measured volume x 100
Table 8: Uncertainty of the masses of sodium chloride
Mass of sodium chloride (g)
Uncertainty of electronic balance (g)
Percentage uncertainty
5.96
±0.01
±0.17%
11.74
±0.01
±0.08%
17.53
±0.01
±0.05%
23.49
±0.01
±0.04%
29.28
±0.01
±0.03%
Percentage uncertainty = uncertainty of the instrument/ measured mass x 100
B. Graphs
Graph 1: Percent of changes in lengths and masses of potato cores
C. Analysis of trends and patterns in the data
As the molar concentration of the solution increases, the percent of changes in both lengths and masses of the potato pieces decreases (the changes in size of the potato pieces are less). The potato pieces in the 1.34M have the lowest percent of changes. The potato pieces in the 0.34M have the highest percent of changes. Both the lengths and masses of the potato pieces follow this pattern. All the values of the percent of changes are positive.
9. Conclusion
This lab work was trying to determine the effect of different concentrations of sodium chloride in solutions on the size of potato cores.
It was expected that the potato pieces put in the solutions with higher concentrations will have less increases in their lengths and masses, comparing to the potato pieces put in solutions with lower concentrations.
50 pieces of potato were put in 5 solutions with different concentrations and left overnight (approximately 10 hours). The final lengths and masses are recorded and compared to the initial measurements.
The data collected showed that the potato pieces in the high concentrated solutions have less increases in their sizes than the potato pieces in the lower concentrated solutions. Surprisingly, only a small portion of the potato pieces loses weight, all of which were put in high concentrated solutions.
The potato pieces put in the lower concentrations (0.34M, 0.67M) increase a lot in sizes because the sodium chloride solutions have more water potential (higher concentration of water) than the cells of the potato, so there was net movement of water, through osmosis, from the solution into the cells of the potato, increasing the sizes of the potato pieces. The cell of the potato has a semi-permeable membrane, thus water molecules can move in and out of the cell, through an integral membrane protein called aquaporin. This passive movement of water from a place with low solute concentration to a place with high solute concentration requires no energy input. The potato pieces put in solutions with high concentrations of sodium chloride have less increase in sizes compared to the other potato pieces. This is because the solutions have lower water potential (lower concentration of water), so there was net movement of water out of the potato cells. This is why some of the potato pieces in higher concentrations of sodium chloride lost weight (pieces E and F in 1.34M solution), and the percent of changes in sizes of the potato pieces in higher concentrated solutions were lower than that of potato pieces in lower concentrated solutions.
The alternative hypothesis is accepted as the data shows that as the concentration of sodium chloride in the solution increases, the mass of the potato cores will decrease or have smaller increase comparing to potato cores put in low concentrated solutions.
10. Evaluation
1. How the procedure could be improved
Change made / Experimental Error
Effect on Data
Possible improvement to decrease error
The uncertainties in the measurements of solute and solvent
The uncertainties in concentrations in the solutions could have affected the movement of water in and out of the potato cells
The uncertainties due to measuring equipment are unavoidable
The uncertainties in the sizes of the potato pieces
The potato pieces were not completely equal in sizes
Measure the potato pieces more carefully and cut with more accuracy
Whether or not the sodium chloride was completely dissolved in the solutions
The sodium chloride might have not dissolve completely in higher concentrated solutions, and thus when the solutions were divided, the concentrations might be unequal
Mix the solution separately so that division is not needed, with lower solute concentrations
The miscalculations of the amount of sodium chloride to be put in each solution
Because the miscalculations, the concentrations of the solutions were quite high (up to 1.67M) instead of starting at 0.1M to 1M
Calculate the mass of sodium chloride put in the solutions accurately using the same formula
Duration of the experiment
The experiment was run for only 10 hours, so the movement of water in and out of bigger potato pieces might have not happened as fast as with smaller potato pieces
Run the experiment for longer duration (i.e. 24 hours)
Final measurements of the potato pieces
The potato pieces might have been shifted around during final measurement, which might have affected accuracy. Different people measured the pieces before and after the experiment.
The same person should measure the pieces initially and finally
Outliers
Some data values might have been outliers (some potato pieces had no changes in mass or length)
Leave out the outliers when analyze the data
2. Reliability and validity of the methodology / procedure AND data
(method/procedure : reliability) The procedure was accurate. The measuring instruments were the best available. There were inaccuracy in measuring the mass of sodium chloride to put in the solutions, and there were uncertainties in the molar concentrations of the solutions. The sample size was large enough to give a meaningful result. There were carelessness in measuring and recording some of the data. Enough measurements were taken and sufficient data was recorded.
(method/procedure : validity) The procedure allow for measurement of relevant data. All procedures and measuring equipment were appropriate. Controlled variables were constant throughout the experiment, to the best of our abilities.
(results/data : reliability) The results are as accurate as the measuring equipment allow. The results are not quite what was expected because of miscalculations in preparations of the solutions. The results were detailed enough and enough data were collected.
11. Questions for Further Research
This lab work could be extended further by an investigation of the rate of osmosis in different plants in the same sodium chloride solution. Crop plants like potatoes could be compared to fruit plants like oranges or apples, or the leaves of tropical plants can be compared to the leaves of plants in colder climate, etc.
12. Bibliography
Campbell , N. A., J. B. Reece, et al. AP Edition Biology. Eighth edition. San Francisco: Pearson Education Inc., 2008. Print.
Davala, Steve. Simple Science Experiment: Osmosis with Potato Slices. Apr 2013. Web. 7 Feb 2014.
Siebrits, Tessa. How to write a good lab report. 2014. Web. 3 Feb 2014
1. Research Question/ Aim
How do the different sodium chloride concentrations of solutions affect the length (measured in mm) and mass (measured in grams) of potato cores placed in them overnight (approximately 10 hours)?
2. Hypothesis
Alternative hypothesis: As the concentration of sodium chloride in the solution increases, the mass of the potato cores will decrease. If the solution they are in has a lower water potential than the potato cores, there will be net movement of water out of the potato cores. If the solution has a higher water potential than the potato cores, there will be net movement of water into the potato pieces. Therefore, potato cores in less concentrated solutions will gain more weight …show more content…
than the potato cores in more concentrated solutions.
Null hypothesis: Different sodium chloride concentrations in solutions have no effects on the mass of the potato cores.
3. Analysis of Variables
Type of Variable
Details
Notes on how variable is manipulated / measured / controlled
Independent (manipulated)
Sodium concentration of the solutions
Different amount of salt (sodium chloride) is put in the solvent (water) to make 0.34M, 0.67M, 1M, 1.34M, 1.67M solutions.
Dependent (responding)
Final mass of potato pieces
Measured at the end of the experiment with a ruler (in mm) and an electronic balance (in gram).
Controlled variables
Volume of solutions
Each solution is mixed with 300 cm3 of solvent (water) and then divided into two beakers with 150 cm3 in each.
Room temperature
All beakers are kept in the same room, so that they all experience the same conditions.
Type of potato
All the potato pieces come from potatoes bought at a store, packaged together.
Initial sizes of potato pieces
Measured before putting the pieces into the solutions with a ruler (in mm) and an electronic balance (in gram).
Temperature of the solutions
All the beakers were kept in the same place, so the solutions experienced the same conditions.
Size and material of the beakers
The 500 ml beakers were made of glass.
Duration of time the potato is left in the solutions
The potato pieces were left in the solutions overnight, approximately 10 hours.
4. Background …show more content…
Information
Osmosis can be defined as the movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration.
The semi-permeable membrane allows small particles through it but does not allow large particles such as sodium chloride. Osmosis will continue until a state of equilibrium is reached i.e. there is no area with a higher or lower concentration than another area.
To land plants, water and osmosis are vital as they play leading roles in the structural support of a plant, they facilitate transport of materials, etc. Lack of water will lead to a plant wilting and possibly dying.
When a cell is in a hypotonic solution (more solute concentration than the cell), water will move from the hypertonic solution (less concentrated) to the hypotonic solution via the process of osmosis.
In this experiment, the movement of water in and out of potato cells left in sodium chloride solution will be investigated. The sodium chloride molecule is too large to be passively transported across the cell membrane, so only net movement of water will happen without any input of energy.
5. Apparatus/Materials
2 x potatoes
1 x bag of salt (sodium chloride)
10 x 500 ml glass
beakers
1500 cm3 of water
500 ml measuring cylinders
30 cm plastic ruler
Electronic balance
Knife
Cutting board
Tweezers
Stirring rod
6. Method/Methodology/Procedure
A. Preparation of solutions
1. The molar mass of sodium chloride is 58.44 g/mol.
Molar concentration = moles of solute/ volume of solution in liters
1M sodium chloride solution = 58.44g sodium chloride in 1 liter of water.
0.34M sodium chloride solution = 19.87g sodium chloride in 1 liter of water
= 5.96g sodium chloride in 300 cm3 of water
Molar concentration
Sodium chloride (g)
Water (cm3)
0.34M
5.96
300
0.67M
11.74
300
1M
17.53
300
1.34M
23.49
300
1.67M
29.28
300
2. Mix the solutions and then divide each solution into two 500 ml glass beakers, each containing 150 cm3 of solution.
3. Label the beakers with the concentration of each solution. There are two beakers for each concentration of sodium chloride.
B. Preparation of the potato cores
1. Wash and dry the potatoes. Peel the potatoes.
2. Cut the potatoes into pieces of equal lengths using a sharp knife. The pieces should be rectangular cuboid. Be as precise as possible. Prepare 50 pieces (10 for each solution).
3. Using a ruler and an electronic balance, measure the length (in millimeters) and mass (in grams) of each potato pieces. Record these initial measurements.
4. Using tweezers, carefully place the 5 potato pieces into each beakers and mark their positions. Avoid moving the beakers too much.
5. Put the beakers away in an undisturbed place. The potato pieces can be put into the beakers at the place where they will be left overnight in order to avoid shifting the potato pieces.
7. Data Collection
Table 1: The initial and final lengths (mm) and masses (g) of potato pieces put in 0.34M sodium chloride solution for 10 hours
Molar concentration: 0.34M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
41
45
+4
2.91
3.32
+0.41
B
40
45
+5
2.94
3.22
+0.28
C
41
43
+2
2.32
2.58
+0.26
D
42
45
+3
3.02
3.37
+0.35
E
41
41
0
2.34
2.55
+0.21
F
40
41
+1
2.56
2.88
+0.32
G
41
41
0
2.63
2.98
+0.35
H
42
44
+2
3.48
3.91
+0.43
I
40
44
+4
3.08
3.39
+0.31
J
41
45
+4
2.86
3.27
+0.41
Table 2: The initial and final lengths (mm) and masses (g) of potato pieces put in 0.67M sodium chloride solution for 10 hours
Molar concentration: 0.67M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
36
37
+1
1.28
1.35
+0.07
B
37
39
+2
2.50
2.64
+0.14
C
37
39
+2
1.59
1.67
+0.08
D
37
38
+1
1.80
1.89
+0.09
E
39
40
+1
1.74
1.86
+0.12
F
39
42
+3
1.85
1.98
+0.13
G
39
41
+2
1.39
1.52
+0.13
H
37
40
+3
1.96
2.09
+0.13
I
37
40
+3
1.99
2.13
+0.14
J
38
41
+3
2.59
2.76
+0.17
Table 3: The initial and final lengths (mm) and masses (g) of potato pieces put in 1.0M sodium chloride solution for 10 hours
Molar concentration: 1.0M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
42
42
0
1.77
1.85
+0.08
B
44
44
0
2.13
2.20
+0.07
C
44
43
-1
2.67
2.77
+0.10
D
43
44
+1
2.03
2.11
+0.08
E
42
43
+1
2.26
2.34
+0.08
F
42
43
+1
2.38
2.45
+0.07
G
42
43
+1
2.05
2.14
+0.09
H
40
42
+2
1.94
2.01
+0.07
I
40
40
0
1.17
1.20
+0.03
J
40
42
+2
1.29
1.35
+0.06
Table 4: The initial and final lengths (mm) and masses (g) of potato pieces put in 1.34M sodium chloride solution for 10 hours
Molar concentration: 1.34M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
41
41
0
2.83
2.90
+0.07
B
40
40
0
2.75
2.80
+0.05
C
41
40
-1
2.25
2.25
0
D
41
40
-1
2.51
2.52
+0.01
E
40
41
+1
2.44
2.42
-0.02
F
39
40
+1
2.40
2.38
-0.02
G
38
39
+1
2.73
2.73
0
H
37
39
+2
2.31
2.33
+0.02
I
37
37
0
1.79
1.80
+0.01
J
38
37
-1
2.34
2.40
+0.06
Table 5: The initial and final lengths (mm) and masses (g) of potato pieces put in 1.67M sodium chloride solution for 10 hours
Molar concentration: 1.67M
Length (mm)
Mass (g)
Potato piece
Initial
Final
Difference
Initial
Final
Difference
A
39
40
+1
3.31
3.40
+0.09
B
42
42
0
3.06
3.10
+0.04
C
41
42
+1
2.68
2.71
+0.03
D
40
41
+1
3.14
3.21
+0.07
E
41
41
0
2.74
2.80
+0.06
F
41
42
+1
2.26
2.29
+0.03
G
40
40
0
1.91
1.96
+0.05
H
40
41
+1
2.19
2.25
+0.06
I
42
44
+2
2.75
2.82
+0.07
J
42
40
-2
3.18
3.30
+0.12
8. Data Processing and Analysis
A. Calculations
Average initial measurement = sum of all initial measurements/10
Average initial length of potato pieces put in 0.34M solution = (41+40+41+42+41+40+41+42+40+41)/10 = 40.9 (mm)
Percent of change = [(final measurement – initial measurement)/initial measurement] x 100
Percent of change in lengths of potato pieces put in 0.34M solution = average difference/average initial length x 100 = 6.11%
Table 6: Percent of changes in the lengths and masses of the potato pieces
Molar concentration
Average initial
Average difference
Percent of changes (%)
Length (mm)
Mass (g)
Length (mm)
Mass (g)
Length
Mass
0.34M
40.9
2.81
+2.5
+0.33
6.11
11.74
0.67M
37.6
1.87
+2.1
+0.12
5.58
6.15
1M
41.9
1.97
+0.7
+0.07
1.67
3.55
1.34M
39.2
2.43
+0.2
+0.02
0.51
0.82
1.67M
40.8
2.72
+0.5
+0.06
1.22
2.20
Table 7: Uncertainty of the volume of water
Volume of water added to the beakers (cm3)
Uncertainty of the measuring cylinder (cm3)
Percentage uncertainty
300
±1
±0.33%
300
±1
±0.33%
300
±1
±0.33%
300
±1
±0.33%
Percentage uncertainty = uncertainty of the measuring cylinder/measured volume x 100
Table 8: Uncertainty of the masses of sodium chloride
Mass of sodium chloride (g)
Uncertainty of electronic balance (g)
Percentage uncertainty
5.96
±0.01
±0.17%
11.74
±0.01
±0.08%
17.53
±0.01
±0.05%
23.49
±0.01
±0.04%
29.28
±0.01
±0.03%
Percentage uncertainty = uncertainty of the instrument/ measured mass x 100
B. Graphs
Graph 1: Percent of changes in lengths and masses of potato cores
C. Analysis of trends and patterns in the data
As the molar concentration of the solution increases, the percent of changes in both lengths and masses of the potato pieces decreases (the changes in size of the potato pieces are less). The potato pieces in the 1.34M have the lowest percent of changes. The potato pieces in the 0.34M have the highest percent of changes. Both the lengths and masses of the potato pieces follow this pattern. All the values of the percent of changes are positive.
9. Conclusion
This lab work was trying to determine the effect of different concentrations of sodium chloride in solutions on the size of potato cores.
It was expected that the potato pieces put in the solutions with higher concentrations will have less increases in their lengths and masses, comparing to the potato pieces put in solutions with lower concentrations.
50 pieces of potato were put in 5 solutions with different concentrations and left overnight (approximately 10 hours). The final lengths and masses are recorded and compared to the initial measurements.
The data collected showed that the potato pieces in the high concentrated solutions have less increases in their sizes than the potato pieces in the lower concentrated solutions. Surprisingly, only a small portion of the potato pieces loses weight, all of which were put in high concentrated solutions.
The potato pieces put in the lower concentrations (0.34M, 0.67M) increase a lot in sizes because the sodium chloride solutions have more water potential (higher concentration of water) than the cells of the potato, so there was net movement of water, through osmosis, from the solution into the cells of the potato, increasing the sizes of the potato pieces. The cell of the potato has a semi-permeable membrane, thus water molecules can move in and out of the cell, through an integral membrane protein called aquaporin. This passive movement of water from a place with low solute concentration to a place with high solute concentration requires no energy input. The potato pieces put in solutions with high concentrations of sodium chloride have less increase in sizes compared to the other potato pieces. This is because the solutions have lower water potential (lower concentration of water), so there was net movement of water out of the potato cells. This is why some of the potato pieces in higher concentrations of sodium chloride lost weight (pieces E and F in 1.34M solution), and the percent of changes in sizes of the potato pieces in higher concentrated solutions were lower than that of potato pieces in lower concentrated solutions.
The alternative hypothesis is accepted as the data shows that as the concentration of sodium chloride in the solution increases, the mass of the potato cores will decrease or have smaller increase comparing to potato cores put in low concentrated solutions.
10. Evaluation
1. How the procedure could be improved
Change made / Experimental Error
Effect on Data
Possible improvement to decrease error
The uncertainties in the measurements of solute and solvent
The uncertainties in concentrations in the solutions could have affected the movement of water in and out of the potato cells
The uncertainties due to measuring equipment are unavoidable
The uncertainties in the sizes of the potato pieces
The potato pieces were not completely equal in sizes
Measure the potato pieces more carefully and cut with more accuracy
Whether or not the sodium chloride was completely dissolved in the solutions
The sodium chloride might have not dissolve completely in higher concentrated solutions, and thus when the solutions were divided, the concentrations might be unequal
Mix the solution separately so that division is not needed, with lower solute concentrations
The miscalculations of the amount of sodium chloride to be put in each solution
Because the miscalculations, the concentrations of the solutions were quite high (up to 1.67M) instead of starting at 0.1M to 1M
Calculate the mass of sodium chloride put in the solutions accurately using the same formula
Duration of the experiment
The experiment was run for only 10 hours, so the movement of water in and out of bigger potato pieces might have not happened as fast as with smaller potato pieces
Run the experiment for longer duration (i.e. 24 hours)
Final measurements of the potato pieces
The potato pieces might have been shifted around during final measurement, which might have affected accuracy. Different people measured the pieces before and after the experiment.
The same person should measure the pieces initially and finally
Outliers
Some data values might have been outliers (some potato pieces had no changes in mass or length)
Leave out the outliers when analyze the data
2. Reliability and validity of the methodology / procedure AND data
(method/procedure : reliability) The procedure was accurate. The measuring instruments were the best available. There were inaccuracy in measuring the mass of sodium chloride to put in the solutions, and there were uncertainties in the molar concentrations of the solutions. The sample size was large enough to give a meaningful result. There were carelessness in measuring and recording some of the data. Enough measurements were taken and sufficient data was recorded.
(method/procedure : validity) The procedure allow for measurement of relevant data. All procedures and measuring equipment were appropriate. Controlled variables were constant throughout the experiment, to the best of our abilities.
(results/data : reliability) The results are as accurate as the measuring equipment allow. The results are not quite what was expected because of miscalculations in preparations of the solutions. The results were detailed enough and enough data were collected.
11. Questions for Further Research
This lab work could be extended further by an investigation of the rate of osmosis in different plants in the same sodium chloride solution. Crop plants like potatoes could be compared to fruit plants like oranges or apples, or the leaves of tropical plants can be compared to the leaves of plants in colder climate, etc.
12. Bibliography
Campbell , N. A., J. B. Reece, et al. AP Edition Biology. Eighth edition. San Francisco: Pearson Education Inc., 2008. Print.
Davala, Steve. Simple Science Experiment: Osmosis with Potato Slices. Apr 2013. Web. 7 Feb 2014.
Siebrits, Tessa. How to write a good lab report. 2014. Web. 3 Feb 2014