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In our lab we attempted to answer the question
of if surface area affected osmosis rates. To
accomplish this we created 4 different shapes
out of potato, each with equal mass, and put
them in a 5% salt water environment. After 30
minutes we observed their new masses.
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We first cut the potato into 4 shapes of equal
mass. We then took the measurements of all the
shapes in order to calculate the surface area.
After that we created a 5% salt solution by first
placing 15 grams of salt in a beaker and then
filling it until the total volume was 300 ml.
After placing the potatoes in these solutions we
waited 30 minutes for osmosis to occur.
We then weighed the potatoes in order to
compare the difference in weight.
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The molarity of the salt solution was one of the
controlled variables because it was at 5% in all
4 cups
The shape of the potato and its surface area
was the only experimental variable.
Temperature was a controlled variable because
it was at room temperature for all 4 cups.
There was no control because there is no
standard shape for a potato.
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All 4 shapes weighed 6.5 grams before they
were placed in the 5% salt solution.
After they were placed in the salt then the cube
weighed 6.4 grams, the pyramid weighed 6.0
grams, the cylinder weighed 5.7 grams and the
rectangular prism weighed 5.7 grams.
The surface area of the shapes were 17.9 cm
squared for the cube, 20 cm squared for the
pyramid, 16.49 cm squared for the cylinder and
34.02 cm squared for the rectangular prism
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The dimensions of the cube in cm were: Base =
2 Height = 1.7 and Width = 1.5.
The dimensions of the pyramid were: Base = 4
and Height = 3.
The dimensions of the cylinder were:
Radius = .5 and height = 4.75.
The dimensions of the rectangular prism were:
Height = .3 Base = 4.2 Width = 3.5
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The percent change for the cube was 1.5%
It was 7.7% for the pyramid.
It was 12.3% for the cylinder.
It was 12.3% for the rectangular prism.
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The purpose of this lab was to see if there was a
correlation between an objects surface area and
shape with the speed at which osmosis occurs.
We found that the shape of the object and the
shortest distance to the center had more effect
on osmosis then the surface area. The
rectangular prism and cylinder have a very
small distance from the outside to center so
their weight changed the most (.8 grams each)
while the cube and pyramid had a longer
distance to the center so their weight changed
less (.1g and .5g)
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Our hypothesis was that the rate at which
diffusion occurred would be proportional to
the surface area but it wasn’t so our hypothesis
didn’t agree with the results.
There were many things that could have gone
wrong in our experiment but the main
problems were that we couldn’t cut the potato
accurately with a ruler and the scale we were
using didn’t work properly.