Investigation showing the effect of changing the concentration of salt in water on the weight
of cucumber slices
Introduction – 0,5 A4 typewritten.
The aim of this investigation is to see how salt concentrations affect the weight of cucumber slices.
This will be done by pouring different moles of salt in 5 beakers of water and immersing cucumber
slices within the saline solutions for 10 minutes. The weight of the cucumber slices will be taken
before placing them in the solution and after to see the change in weight due to the gain or loss of
water
The gain or loss of water is called osmosis. Osmosis is specifically the diffusion of water through a
semipermeable membrane. A semipermeable membrane is a surface that selectively allows materials
to pass through it. In the case of osmosis, semipermeable membranes block solutes from diffusing
through the membrane while still allowing solvents to pass through therefore, when something, like a
cucumber slice, is placed in a solvent like water, the water molecules within the cucumber slice and in
the water constantly move back and forth through the cucumber’s membrane.
Salt, a solute, is made of sodium (which has a positive charge) and chloride (which has a negative
charge) whereas water has partial charges. Due to this, when salt is added to the water, the sodium
and the chloride both attract water molecules, leaving less water molecules to enter the cucumber
slice. The exchange of the water inside the cucumber slice and in the solution entering each other
would be imbalanced (since all water molecules within the cucumber slice are free to exit the
cucumber slice without being attracted to a solute).
(The left side is the cucumber slice, the yellow line in the middle is the membrane and the right side is
the salt solution. The blue circles are water molecules and the pink circles are salt)
This means that organic matter placed in solutions lose more weight the higher the concentration of
salt. This process of water(or other solvents) moving from a lower concentration of solute to a higher
concentration is called osmosis.1
If the organic matter being put in the solution contains more of the solute than the solution does, then
the solution is hypotonic. This means that a lot of the water molecules inside the organic matter are
unable to leave the cell and enter the solution since they’re attracted to the solute. However, the
decreased flow of water molecules from the organic matter doesn’t affect the flow of water molecules
from solution. Naturally, this would increase the weight of the organic matter since more water
molecules are entering it than the water molecules exiting it. Hypertonic solutions have more solute
molecules than the organic matter being submerged in it. Due to that, the organic matter loses more
water molecules than it gains thereby losing weight. Isotonic solutions have the same amount of
water and solute molecules as the organic matter. Since the concentrations are at an equilibrium, a
similar amount of water molecules diffuse from the water and into the water so there is no major
weight change.2
Hypothesis:
Research question: What is the effect of varying concentrations of salt on the weight of cucumber
slices?
I hypothesize that the effect of changing the concentration of salt in water on the weight of cucumber
slices is that as the concentration of salt in the beakers of water increases, the cucumber slices will
lose more weight. This is because hypertonic solutions prevent the water molecules in the solution
from entering the cucumber slices (since they’re too attracted to the sodium and chloride particles)
while water particles still diffuse from the cucumber slices into the solution.
Variables:
Independent variable (I.V): The concentration of salt in the water
● The different amounts of salt used are 0g, 5.8g, 11.68g, 23.36g and 35.04g
● The salt is measured using a weighing scale
● Units: Grams (g)
Dependant variable (D.V): The weight of the cucumber slices
● The weight of every slice will be measured before it’s immersed in the solutions and after to
see the change
● The weight is measured using a weighing scale
● Units: Grams (g)
1
"what is osmosis? (video) | Khan Academy." 24 Mar. 2021,
https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-a
nd-osmoregulation/v/osmosis. Accessed 2 Oct. 2021.
2
"Tonicity: hypertonic, isotonic & hypotonic solutions (article) | Khan."
https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-a
nd-osmoregulation/a/osmosis. Accessed 2 Oct. 2021.
Control variables
Why should it stay the same?
Amount of water
If there is more water in a By measuring 200ml of water
solution than there should be, for every beaker using the
the solution would be more measure lines on each beaker
diluted and the cucumber slice
would lose less weight.
Difference in cucumber slices A thicker slice of cucumber
among the different tests and would weigh more than a
trials
thinner slice of cucumber that
was soaked in the same
solution regardless of whether
or not the slices lost weight.
The slices have to be the same
weight before putting them in
the beakers in order to avoid
this.
How will you keep it the same?
Since
ensuring
that
the
cucumber slices are the same
weight is tedious, the cucumber
slices will be weighed before
placing them in the solution
and again after soaking in the
solution. This way, the change
in weight is documented rather
than the actual weight of the
slices.
How long the cucumber slices If certain cucumber slices soak Once the cucumber slices are
are soaked in the water
for longer, they’ll have more dropped in their respective
time to diffuse and lose weight. beakers, a timer will be set for
10 minutes.
The solute that is used0
Although very close, sugar is a Only salt will be used for this
little bit better at diffusing than experiment.
salt so an inconsistency in the
solute used would lead to
carrying water loss or gain from
the cucumber slices.
The organic matter put in the Slugs for example dehydrate
solution3
from salt in just a few minutes
whereas cucumber slices take
around 20 minutes to decently
dehydrate
(depending
on
solute levels).
Since different organic matters
vary so drastically in terms of
how quickly they dehydrate,
only cucumber will be used as
the organic matter in the
experiment.
Materials:
13x Cucumber slices (thinly sliced)
1x Knife
5x 250ml beakers
3
"Salt vs. Sugar – A Dissolving Problem | Chemical Education Xchange." 12 Aug. 2020,
https://www.chemedx.org/article/salt-vs-sugar-%E2%80%93-dissolving-problem. Accessed 2 Oct. 2021.
1x Weighing scale
Tissue paper
5x Glass stirring rods
1x Timer/ stopwatch
1 litre of water
75.88g of salt
1x Paper
Method:
1. Gather the ingredients
2. Fill 5 beakers with 200ml of water each
3. Draw 5 circles on a large piece of paper that the bottoms of the beakers fit in
4. Calculate the moles per liter of salt required for each beaker
5. Measure each amount of salt on a weighing scale ( 0g, 5.8g, 11.68g, 23.36g and 35.04g)
6. Write 0g on the first circle, 5.8g on the second, 11.68g on the third, 23.36g on the fourth and
35.04g on the fifth
7. Place a beaker on each of the circles
8. Refer to the grams of salt written underneath each beaker and pour that amount in each (0g in
the first beaker, 5.8g in the second, 11.68g in the third, 23.36g in the fourth and 35.04g in the
fifth)
9. Using a knife, slice each cucumber slice in half (making 26 slices)
10. Discard of 1 of the 26 slices, leaving only 25
11. Using a knife, make 1 notch in 5 of the cucumber slices
12. Make 2 notches in 5 of the cucumber slices
13. Make 3 notches in 5 of the cucumber slices
14. Make 4 notches in 5 of the cucumber slices
15. Make 5 notches in 5 of the cucumber slices
16. Weigh each cucumber slice and mae note of which one weighed how much
17. Pat all the cucumber slices dry with a tissue paper
18. Place 5 cucumber slices (with 1 slice of each kind of notched slice) in each beaker
19. Start a timer for 10 minutes
20. Gently stir each of the beakers using stirring rods being sure not to hit the cucumber slices
and breaking them
21. After 10 minutes, take the cucumber slices out and pat them dry with tissue paper
Weigh each slice of cucumber again and record the data
Raw data:
This is the data collected on the day of the experiment, organized into neat tables with headings and
units. You must report raw data, and not just the means or % mass change. Include any qualitative
data (observations). Uncertainties should be included in the table column headings:
Research table showing the effect of changing the concentration of salt in water on the weight of
cucumber slices
-
The difference between the weight before soaking the slices in the water in comparison with
after is 𝑤𝑒𝑖𝑔ℎ𝑡 𝑎𝑓𝑡𝑒𝑟 𝑠𝑜𝑎𝑘𝑖𝑛𝑔´ − 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡.
E.g Test 1 Trial 1 would 1.957-1.868 which is 0.089
-
The percentage difference is the
𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡
E.g Test 1 Trial 1’s difference is 0.089.
0.089/1.868 = 0.047644…
0.047644… x 100 = 4.764% (rounded to the 3 decimal place)
-
The mean percentage difference (percentage difference will be referred to as z) is (z1 + z2 +
z3 + z4 + z5)/5 with z1, z2 etc being the 5 trials for 1 test.
E.g
Processed data:
This is what you do to the data in order to interpret it. This could include making means, calculating
percentages or rates, and plotting data on graphs. You must explain in this section how you have
processed your data. For this lab, you do not need to provide error bars on the graph, but should be
working with the means of your three replicates. Ensure consistent use of significant figures, units and
clear headings on all axis labels and tables. All graphs and tables need clear explanatory headings.
The data has been formatted as a line graph because this experiment is measuring the change in one variable due
to one other variable. When there’s two variables being compared against each other, line graphs are used since
it shows what weight the slices were for each salt amount and the percentage change it had at the same time.
This graph consists of the mean percentage differences to observe the gain or loss of weight the cucumber slices
experienced in the salt solutions. The mean percentage difference, calculated from five data points of the same
circumstances, is taken to ensure a more accurate result because even if one of the cucumber slices in a beaker
was somehow irregular, the other four slices will make the average normal regardless. If the 5 slices have
varying results with a broad range, the average would take the middle as a compromise between the data points.
That way, all 5 of the trials are represented, taking account for the range that organic matter usually has in real
life. Behind the blue line is a linear line of best fit which shows the mean path that the data points take. The line
of best fit serves a similar purpose to the means for the percentages. It shows the average path that the data
points are being plotted as. The y-axis depicts the percentage change with minus percentages being a decrease
in mass.
Conclusion:
State a clear conclusion, with an explanation based on your data. It is a good idea to refer directly to your data
in the conclusion. Ensure that it addresses the RQ.
What is the effect of varying concentrations of salt on the weight of cucumber slices?
The effect is that the greater the concentrations of salt, the higher the percentage change.The line of best fit
supports this lab’s hypothesis as the percentage change is a linear decrease that becomes negative since the
slices lose more weight. A specific example is the second data point which decreased by 14.9% whereas the
next data point has a 23.81% decrease. The line of best fit decreases gradually because the increased salt
concentration in the hypertonic solution meant there were more salt particles that attracted the surrounding
water particles, causing less water to be able to move in the solution. The water molecules from the cucumber
slices however were less obstructed and therefore flowed naturally. Water molecules naturally flow in and out of
membranes so the water molecules in the cucumber slices enter the salt solution but a mere few water molecules
from the solution enter the slice since many of them are attached to the salt particles. If there are more particles,
less water from the salt solutions can enter the cucumber slices which means that the slices are only released
water particles, causing a loss in weight. This explains why more weight is lost as the amount of salt in the
solution increases. The increase in weight at 0g of salt can be explained by the fact that the water and cucumber
mixture is a hypotonic mixture. Although the water had no salt, cucumber naturally contains a little sodium
which attracts some water molecules within the cucumber slice thereby making the exchange of water
molecules between the cucumber and the water it’s soaked in unequal because the cucumber is gaining more
water molecules than it’s releasing. There aren’t any plotted points that stand out as particularly anomalous
since none of them are actually on the line of best fit. The 3rd percentage difference is similar to the 5th so the
line might have plateaued there had it not been the 4th data point making it a decent contender for an anomalous
data point. However, why the 4th data point stands out cannot be explained. Another experiment conducted
with the same premise in which they had 2 glasses of water (1 distilled and 1 with salt) and they soaked
cucumber slices in them for 2 hours. They found that after 2 hours, the cucumber in the saline solution lost 3
grams whereas the cucumber in the distilled water gained 2 grams.4 The percentage change for the saline
solution’s cucumbers was -11.539% and the percentage change for the distilled water soaked cucumbers was
9.091% (rounded to 3 decimal points). If Test 1 and Test 5 (Test 5 being the comparison for the other
experiment’s saline solution since their amount of salt was unspecified) had been left for 2 hours as well instead
of 10 minutes, their percentage changes would be -42.454% for the saline solution and 57.173% for the distilled
water’s cucumbers (rounded to 3 decimal points). Both saline solution soaked cucumbers decreased in weight
and the other cucumber slices gained weight due to the sodium in the slices but this lab’s results had more
drastic results. This could be because. Another experiment was conducted where cucumber slices weren’t
placed in saline solution, salt was simply sprinkled atop the cucumber slices. Similar to how the high
concentrations of salt led to a loss in weight in this lab, the sprinkled salt in their experiment drew out the
moisture in the cucumber. 5 This is because the salt sprinkled on top will mix with the water on the surface of
the cucumber slices, making a saline solution with high concentrations of salt. This, through osmosis, drew the
water from the cucumber slices since the salt sprinkled on top has far more salt than the insides of the cucumber
slices, leading to a loss in weight. Both of these experiments (although not down to the numbers) support this
lab’s findings and hypothesis.
Discuss & interpret your data in order to reach a conclusion.
Are there any anomalies ? Can you explain these ?
4
"How to measure osmosis in a cucumber - Think like a scientist (4/10)." 29 Oct. 2014,
https://www.youtube.com/watch?v=dD9dGFrFcoo. Accessed 5 Oct. 2021.
5
"Cucumber Chemistry: Moisture Capture with Desiccants - Scientific ...." 15 Oct. 2015,
https://www.scientificamerican.com/article/cucumber-chemistry-moisture-capture-with-desiccants/. Accessed 5
Oct. 2021.
Does the data support your hypothesis, based on biological theory ? Explain.
How does this work fit with what other’s have found (context) ? You will need a couple of suitable references
here.
Evaluation:
How do any uncertainties in measurement or other sources of error influence the results ?
What improvements could you carry out, and how would they address the limitations ?
Link the improvements you suggest to the limitations, and explain what they would improve.
Since so many calculations are done for this data (first the difference, then the percentage difference from
which an average is taken), small mistakes such as reading the weighing scale wrong when weighing the before
or afters of the cucumber slices or when weighing the salt or when recording a number wrong in the data can
affect the final data since that one misread goes through so many calculations making it larger and smaller.
Other possible errors are how much the 5 solutions are mixed. If there aren’t 5 people participating in this lab,
it’s impossible for the beakers to all be evenly stirred using the glass rods (unless machinery is used). This could
cause certain beakers’ cucumber slices to interact with water that isn’t mixed with salt, which would lead to an
increase in weight, whereas cucumber slices that interact with saltier, well mixed waters would lose more
weight. Improvements that could be carried out in order to prevent these limitations would be to read, write, and
calculate all the numbers properly as well as to employ at least 5 members to conduct this experiment
accurately. The 5 members would be required to consistently but gently stir the 5 beakers with the
water-salt-cucumber mixture using glass stirring rods. These alterations would make the data table compiled
even more accurate.