Muhammet Orhun Şahin
11-B No:87
OSMOSIS EXPERIMENT
DESIGN
Research Question
How does the salt or sugar concentration of a solution affect the mass of potato cells?
Hypothesis
As the concentration of salt in the solution increases, the size of potato cells will decrease.
Because the potato cells will lose water by osmosis since the solution which they are in has a lower
water potential than the potato cells. Therefore, potato cells in concentrated solutions will lose
weight but the ones in dilute solutions will gain weight.
Variables
The final mass of potato pieces is dependent variable.
The salt concentration of the solutions is independent variable.
The volume of solutions, the temperature of the lab, the initial lengths of potato pieces, the
initial volume of potato pieces, the initial surface area of the potato pieces, the initial masses of
potato pieces, the species of the potato, the temperature of the water in the solutions, the size and
material of the beakers and the time for which potato chips stay in the solution are controlled
variables.
The Procedure
1. A single potato is taken and all the samples are cut from the same potato. So the species of
the potato is controlled.
2. The potato is soyuldu.
3. 4 samples of potato are cut from the potato by using a knife. By a ruler and a board marker
the dimensions of potato pieces are marked on the potato. The measurement are taken for
three times by the ruler and then, they are marked. So 4×3×1 potato pieces are cut from the
potato. Therefore, the initial length, the initial volume and the initial surface areas of the
potato pieces are controlled.
4. After that the masses of the potato pieces are measured by an electronic balance and they
are noted. It was found that the initial masses were quite close to each other so the initial
masses of the potato pieces are controlled, too.
5. 4 identical beakers of 500 ml are taken. The beakers are washed and left to dry. So the size
and material of the beakers are controlled.
6. By using a graduated cylinder 100 ml of water is taken from the tap and it is poured into the
beaker. This is repeated 3 times for each beaker. So each beaker now contains 300 ml of
water. Therefore, the volume of solutions and the temperature of solutions are controlled
7.
8.
9.
10.
since water from the same tap in a short period of time is used. To avoid parallax error a
perpendicular view to the scale of the graduated cylinder is used.
Then, 10 grams of salt is measured by using the electronic balance and an evaporating dish.
The salt in the evaporating dish is added to the first beaker, it is dissolved by a stirrer and the
beaker is labeled 1.
The same process is repeated to measure 20 grams of salt and 10 grams of sugar and the
beakers are labeled 2 and 3 respectively. The last beaker only contains water from the tap
and it is labeled 4. It is used as the control group.
Then, one potato piece is added to each 4 beakers. And the stopwatch is started. Since the
experiment takes place in the lab, the outside temperature and pressure are also controlled.
At the end of 40 minutes the solutions in the bakers are poured to the sink and the masses of
the pieces are measured by an electronic balance and their final masses are noted.
Apparatus
4 beakers
Tap water
1 potato
Table salt
Sugar
Knife
A stopwatch
Patates soyucu
Ruler
Boardmarker
Graduated cylinder
Evaporating dish
Stirrer
DATA COLLECTION AND PROCESSING
Recording raw data
Uncertainty of the volume of water
Volume of water added to the
beakers(ml)
300
300
300
Uncertainty of the graduated
cylinder
±1 ml
±1 ml
±1 ml
Percentage uncertainty
±0.33%
±0.33%
±0.33%
300
±1 ml
±0.33%
Uncertainty of the masses of salt and sugar
Mass of salt or sugar(g)
0.00
10.00
20.00
10.00
Uncertainty of electronic
balance
±0.01 g
±0.01 g
±0.01 g
±0.01 g
Percentage uncertainty
± 0.00 %
±0.10%
±0.05%
±0.10%
To calculate the percentage uncertainty, the measured mass is divided by the uncertainty of
the instrument and multiplied by 100.
Uncertainty of the concentration of the solutions
Mass of sugar or salt(g)
Volume of water(ml)
0.00± 0.00%
10.00±0.10%
20.00±0.05%
10.00±0.10%
300±0.33%
300±0.33%
300±0.33%
300±0.33%
Concentration of the
solutions(g ml-1)
0.00±0.33%
0.03±0.43%
0.07±0.38%
0.03±0.43%
To find the concentrations of the solutions, the mass of the sugar or salt is divided by the
volume of the water in the beakers.
To find the uncertainty of the concentration, the percentage errors of the mass of the salt or
sugar and the volume of the water are added together.
Initial and final masses of potato pieces
The initial
mass of
pieces(g)
(±0.01g)
8.88
8.87
8.55
8.22
The
percentage
uncertainty of
the initial
mass
±0.11%
±0.11%
±0.12%
±0.12%
The final mass
of the
pieces(g)(
±0.01g)
The
percentage
uncertainty of
the final mass
The change in
mass(g)
8.06
7.85
8.60
8.73
±0.12%
±0.13%
±0.12%
±0.11%
-0.82
-1.02
+0.05
+0.51
The
percentage
uncertainty of
the change in
mass
±1.22%
±0.98%
±20%
±1.96%
To find the percentage error of the mass of the potatoes the uncertainty 0.01 is divided by
the measured values and multiplied by 100.
To find the change in masses of potatoes the initial mass is subtracted from the final mass.
To find the percentage error in the change in masses of the potatoes the uncertainty 0.01 is
divided by the calculated results and the results are multiplied by 100.
CONCLUSION
In Beaker 4 there was no salt or sugar. It only contained tap water. The mass of potato piece
in it increased by 0.51 grams. This shows that the potato piece gained water by the process of
osmosis since it was in a hypotonic solution.
In beaker 1 there was 10 grams of salt and 300 ml of water. The mass of the potato piece in it
decreased by 0.82 grams. This shows that the potato piece lost water by the process of osmosis since
it was in a hypertonic solution.
In beaker 2 there was 20 grams of salt and 300 ml of water. The mass of the potato piece in it
decreased by 1.02 grams. This shows that the potato piece lost water by osmosis since it was in
hypertonic solution. When compared with beaker 2, the piece in beaker 3 lost more water because
the solution in beaker 3 was more concentrated. It shows that the more concentrated a solution is,
the more water loses the potato piece.
In beaker 3 there was 10 grams of sugar and 300 ml of water. The mass of the potato piece in
it increased by 0.5 grams. This shows that the piece gained a little water by osmosis since it was in a
hypotonic solution. The potato piece is more concentrated in terms of sugar than the solution in the
beaker.
Overalls, my data shows that if cells are in a more concentrated solute solution then, they
lose water. If they are in a less concentrated solute solution then, they gain water. My data is good
enough to show that. And the bar graph shows the trend clearly. Also it supports the osmosis theory
in the book “IB Study Guides Biology, Andrew Allot, Oxford Press”.
However there are some errors in my experiment. All the potato pieces were not of equal
surface area or equal mass. So osmosis occurs to different extends for each potato. Also I could not
start the experiment at the same time for each potato piece. I dropped the pieces to each beaker
one by one so the first piece I dropped had more time to stay in the solution. The same error
occurred while collecting the pieces from the beakers. Additionally, I measured the volume of water
by graduated cylinder. Its limit of reading is 1 ml. I could use a more accurate instrument to measure
the volume of water. Also some salt precipitated in the solution while waiting for osmosis to take
place. It also caused errors.
To improve my data, I should have used a cubic slicer to cut potato pieces of equal sizes and
masses. Also I should have asked for help from a few of my friends to stir the solutions with me to
prevent the salt from precipitating. Additionally, I should have collected the piece the first which I
dropped in the solution the first. And I should have collected the piece the last which I put in the
solution the last. So each piece would have the same time in solutions.