Potato Cylinder Experiment

Method:

To start with, all equipment that was required was gathered up. Six
screw top bottles, a pipette, a couple of beakers, a marker pen,
cocktail sticks, cutting tiles and scalpels were collected. Several
6cm to 9cm potato cylinders were then taken from some normal potatoes.
These longer cylinders were then cut into 18, 2cm lengths using a
scalpel. An average weight of the smaller potato cylinders was then
taken and both the length and weight of these cylinders were recorded.
The 2cm lengths were then split into six groups of three to make it
easy to record three sets of results from each tube of solution. To
tell the difference between the three different potato lengths in each
tube, cocktail sticks were used. 'Group one' potato cylinders were
left as they were, 'group two' potatoes had a piece of cocktail stick
in one end of the cylinder and 'group 3' had a piece of cocktail stick
in each end.

With the potato cylinders ready to be used, six different strengths of
stock solution were made up in six screw top bottles. There was 10ml
of solution in each bottle. One had distilled water in, then one with
strength of 0.2 molar, then 0.4 M, 0.6 M, 0.8 M and finally 1 M. The
solutions were made as follows: distilled water was just 10ml of
distilled water and the 1 molar solution was just 10ml of stock
solution. The 0.2 molar solution was 2ml of stock solution and 8ml of
distilled water. The 0.4 molar solution was 4ml of stock solution and
6ml of distilled water. The 0.6 molar solution was 6ml of stock
solution and 4ml of distilled water. Finally, the 0.8 molar solution
was 8ml of stock solution and 2ml of distilled water. The bottles were
labelled with a marker pen with the strength of solution they
contained. One potato from each 'group' was then placed in each
bottle, placing three potato cylinders in each bottle. The bottles
were then left for two days to allow results to be taken. After the
two days, each potato cylinder was re-measured and re-weighed and any
observations were recorded.

Results:

One some of the potato cylinders (mainly on the solutions above 0.6
Molars) there was some black discolouring. This is the start of
decomposition on the potato and maybe signifies that the potato
lengths were left in the solutions too long.

Length (cm)

Length Change (cm)

Mass (g)

Mass Change (g)

Potato 1

Potato 2

Potato 3

Average Change

Potato 1

Potato 2

Potato 3

Average Change

Start Measurements

2

2

2

N/A

1.18

1.17

1.17

N/A

Distilled Water

2.3

2.2

2.2

+0.2

1.37

1.37

1.43

+0.22

0.2 Molars

1.8

1.9

1.8

-0.2

1.06

1.04

0.88

-0.18

0.4 Molars

2

1.8

1.8

-0.1

1.01

1.01

0.94

-0.19

0.6 Molars

1.7

1.9

1.8

-0.2

0.88

1.01

1.01

-0.21

0.8 Molars

1.9

1.8

1.9

-0.1

1.10

0.75

1.11

-0.6

1 Molar

1.7

1.8

1.9

-0.2

0.97

1.02

0.99

-0.18

Analysis:

The evidence given shows, in most cases, that the stronger the stock
solution, the more the potato will decrease in length and weight. This
is quite expected, as it is to do with osmosis and diffusion. Say for
instance, there is a potato cylinder in a stock solution of strength 1
molar. The potato is seen as an area of less concentrated solution and
the stock solution is seen as an area of strong concentration. In the
process of osmosis, particles move from an area of strong
concentration (the stock solution) and into an area of weaker
concentration (the potato) through a partially permeable membrane. As
the stock solution moves into the potato, it causes the potato to
shrivel up as it contains salt, which absorbs the water in the potato
itself. If this process was put to work in the opposite situation (the
potato in distilled water) the water moves into the potato still, but
as there is no salt or absorbent in distilled water, the potato swells
and becomes turgid. This explanation makes gives us a prediction that
is most likely to be true, and this is more or less proven with the
results gathered. Although there are a few anomalous results, both the
graphs and the results table show that where distilled water is used,
the potato becomes turgid and where stock solution is used, the potato
cylinders have become shrivelled and squashy. The evidence that has
been recorded from this experiment supports the prediction drawn out
in the planning stage quite well. Although the anomalous results have
mixed up the evidence slightly, the simple fact that the potato
becomes turgid in distilled water and more squashy and shrivelled in
stock solution is definitely proved by these results.

Evaluation:

The procedure used to obtain these results went very well and I was
more or less able to stick to the plan drawn up before the practical
exactly. Although smaller things like the length of the potato
cylinders and the amount of solution used had to be changed due to
economical reasons, the plan was followed very well. The results
obtained proved my prediction quite well, but there were a few
anomalous results, which strayed from what I thought a bit. These
results could have come around for a few reasons. Maybe the potato was
not cut to exactly the same size as the others or it was lighter or
heavier than the other cylinders. The cylinder may have been left in
the solution slightly longer than the rest of them or maybe the whole
experiment was left too long to record incredibly useful results. If
this procedure was to be carried out again, I would make more repeat
reading to give a wider range of results, maybe four or five repeat
readings instead of three. One thing I would definitely change in the
length of time the potato cylinders were left to show results in.
Because the potatoes were left for maybe a little too long, some of
them started to deteriorate and formed a black discolouring. Instead
of leaving them for two days, I'd leave them for one day if the
procedure were to be carried out again.