# the effect of surface area on diffusion

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```					                                                                                    By Michelle Li 9G

The Effects of Surface Area: Volume Ratio on
Diffusion
Date: 2/3/2011

Partners: Komal Grewal

Aim:     To determine the relationship between the surface area: volume ratio of an object and the
time it takes for a substance to completely diffuse into it.

Hypothesis: That increasing the surface area will increase the diffusion rate because this will
create more contact between the object and the substance.

Variables:
Independent variable: surface area
Dependent variable: time of diffusion
Controlled variables:

- Concentration of acid

- Temperature

- Amount of acid used

Materials:
    Timers
    3 X measured, different sized blocks of agar jelly
    1.0M Sulfuric Acid
    Gloves
    Scalpel
    White tile
    Ruler
    3 X beakers

Method:
1.   Measure 3 different sized blocks of agar jelly (0.5cm³, 0.75cm³ & 1cm³)
2.   Measure 50mL of sulfuric acid into each of the 3 beakers
3.   Put blocks into different beakers
4.   Time how long each block takes for the sulphuric acid to diffuse into it completely
5.   Record results in a table

Safety precautions:
1.          Wear safety glasses to protect eyes from irritants.
2.          Use gloves to protect skin from irritants in agar jelly.
3.          Wear aprons/ lab coats to protect clothing from acid and jelly.
4.          Wash hands after experiment to ensure no traces of irritants.

Results:
Figure 1.

Rate of Diffusion of Different Sized Agar Jelly Blocks.
Agar Block of Jelly (cm³)                            Time of Diffusion (min)
0.5                                                 15:03
0.75                                   Undefined – 3.6% diffused at 16:39
1                                    Undefined – 2.7% diffused at 16:39

Figure 2.

Rate of Diffusion of Different Sized Agar Jelly
Blocks
16:48                                     16:39, 3.6%                 16:39, 2.7%

16:19

15:50
Time (mins)

15:21          15:03, 100%
14:52

14:24

13:55
0.5                       0.75                         1
Agar Jelly Block (cm³)

Discussion:
What is you independent variable?

The independent variable was the surface area : volume ratio of the agar jelly.

The dependent variable is the time it takes for the sulfuric acid to completely diffuse into the agar
jelly.
List two controlled variables in your experiment.

1. Concentration of sulfuric acid
2. Amount of sulfuric acid

Oxygen is used by the body for cellular respiration to make energy. Would oxygen diffuse into or
out of the bloodstream/alveoli? Use the definition of diffusion to explain you answer.

Oxygen would diffuse out of the bloodstream/alveoli into body cells where oxygen leaves the
bloodstream to enter cells and carbon dioxide leaves cells to go into the bloodstream. Which
means that the high concentration of oxygen in the blood is diffused into the cell, where it
becomes low concentrated.

Carbon dioxide is produced by the body when cellular respiration produces useable energy.
Would carbon dioxide diffuse into or out of the bloodstream/ alveoli? Use the definition of

Carbon dioxide would diffuse out of the body cells into the bloodstream where carbon dioxide
leaves the body cells to enter the bloodstream and oxygen leaves the bloodstream to go into the
body cells. The carbon dioxide is high concentrated in the body cells, but diffuses into the
bloodstream and becomes low concentrated.

Using the results from your group, explain whether you would expect the diffusion of oxygen to
occur faster or slower at high altitudes, where the temperatures are usually much colder?

The diffusion of oxygen would occur slower at high altitudes because the temperatures are usually
colder. This was shown in the experiment where the beaker with the cooler temperature (12ᵒ  C)
was unable to completely diffuse in the time given (16:39) and had the lowest percentage of
diffusion (1.9%).

Colder temperatures give less kinetic energy to the particles, therefore slowing down processes (in
this case, diffusion).

What effect would you expect the colder temperatures to have on the breathing rate of
mountaineers in high altitudes? Why?

The colder temperatures will increase the breathing rate of mountaineers in high altitudes because
cold temperature would slow down diffusion. This means that there is less oxygen being diffused,
therefore the mountaineers would need to breathe faster/ harder to obtain more oxygen for their
cells.

What effect did the differences in concentration gradient have on the rate of diffusion? Use your
The higher the concentration gradient, the faster the rate of diffusion. This was shown in the
experiment where the jelly in the beaker using 2M sulfuric acid diffused 20% in 10 minutes,
whereas the jelly in the 0.1M sulfuric acid beaker diffused only 10% in the same time.

The following table shows the pressures of carbon dioxide and oxygen in the air at sea legvel and
at a high altitude, as well as in the body.

Table 1: Pressures of Oxygen and Carbon Dioxide and oxygen in the bloodstream, and in the
atmosphere at high altitudes and sea level.

Pressure of O₂ (mmHg)               Pressure of CO₂ (mmHg)
Bloodstream                                      40                                  45
Atmosphere at sea level                         100                                  40
Atmosphere at high altitude                      50                                  20

a) Would you expect the rate of diffusion of oxygen to increase or decrease at higher
altitudes to sea level? Why?

I would expect the rate of diffusion of oxygen to decrease at high altitudes because there is less
pressure of oxygen in the atmosphere at high altitudes. This means that there is less concentration
of oxygen and the diffusion rate is decreased when there is less concentration of a substance.

b) Would you expect the rate of diffusion of carbon dioxide to increase or decrease at
higher altitudes compared to sea level? Why?

I would expect the rate of diffusion of carbon dioxide to decrease at higher altitudes compared to
sea level because there is less pressure of carbon dioxide in the atmosphere at high altitudes. This
means that there is less concentration of carbon dioxide and he diffusion rate is decreased when
there is less concentration of a substance.

What effect did the size of the cell have on the rate of diffusion?

The more surface area the cell has, the faster the diffusion. This was shown in the experiment
where the smallest block, which had highest surface area (0.5 cm³) completely diffused in 15:03
minutes. Whereas the largest block, which had the lowest surface area (1cm³) was unable to
completely diffuse in the given time (16:39) and only diffused 2.7%.

Would it be an advantage to have larger or smaller lungs at higher altitudes? Why?

It would be an advantage to have smaller lungs at higher altitudes because this means that there is
more surface area of the lung in contact with the diffusing oxygen and carbon dioxide. The larger
the surface area, the faster the diffusion rate and having smaller lungs will give one a larger surface
area of lungs.

Evaluation:
How would you improve your experiment?
I would change the way I tested the hypothesis. For example, my group cut the blocks into 3
different sized blocks and measured the time it took for each to completely diffuse. I think that we
should have used only two blocks (equally sized) and cut one into smaller parts and compared the
time that it took both to diffuse completely. This method would have clearly shown how surface
area affects rate of diffusion, whereas the method that we used did give the desired results, but
was harder to understand.

I would have also done the experiment more times to ensure reliability.

Conclusion:
We were able to determine that by increasing the surface area : volume ratio of an object
increased the rate of diffusion into another substance. The experiment was conducted safely and
successfully and the hypothesis was supported by the results.

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