This lab report summarizes an experiment investigating how surface area affects the rate of diffusion. Agar gel squares with surface areas of 1 cm^2, 4 cm^2, and 9 cm^2 were placed in beakers containing hydrochloric acid. The time taken for the color of each gel square to change, indicating diffusion had occurred, was recorded. The results showed diffusion time decreased as surface area increased, supporting the hypothesis. The largest surface area of 9 cm^2 diffused most quickly, while the smallest 1 cm^2 area diffused slowest. Surface area thus influenced the rate of diffusion as expected.

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INTERNATIONAL BACCALAUREATE
BIOLOGY LAB REPORT
AGAR DIFFUSION TEST
Candidate: Serra Koz
Supervisor: --
May 2014

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BACKGROUND INFORMATION
Solids, liquids and gases consist of particles – atoms, ions and molecules. In liquids and
gases, these particles are in continual motion. The direction that they move in random. If the
particles are evenly spread then their movement in all directions is even and there is no net
movement – they remain evenly spread despite continually moving. Sometimes particles are
unevenly separated – there is a higher concentration in one region than another. This causes
diffusion.
Diffusion is the passive movement of particles from a region of higher concentration to a
region of lower concentration, as a result of the random motion of particles. (Allot,2007, pg.9)
The rate of the diffusion affected by the surface area, volume of the cell, temperature and
concentration gradient. For this experiment the surface area changed, so the effects of surface
area observing. If the surface area increases, then the area of the particles get bigger. Thus, the
particles have a large surface to transportation.
𝑇ℎ𝑒 𝑅𝑎𝑡𝑒 𝑜𝑓 𝐷𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 (𝛥𝑇) ∝
1
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎 (𝑐𝑚2)
AIM: The purpose of this experiment is to consider the effects of surface area in a rate of
diffusion.
RESEARCH QUESTION: How does surface area affects diffusion according to the room
condition (27°C) by using of agar gel which is dried by phenol red, volume of the hydrochloric
acid and same agar gel type?
HYPOTHESIS: The rate of the diffusion affected by the surface area, volume of the cell,
temperature and concentration gradient as mentioned in the background information. If the
surface area of the cell increases, then time of diffusion increases.

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Table 1: Independent, Dependent and Controlled Variables
Independent Variables:
Surface Area of
the Agar gel/cm2
(1x1, 2x2, 3x3)
The surface area of the agar gel measured by the
ruler.
Dependent Variables:
Time of
Diffusion/s Time of diffusion measured by the chronometer.
Room
Temperature
(25°C)
Temperature of the room is same during the
experiment and measured by the thermometer.
If the temperature change the rate of time can be
changed as well.
Controlled Variables:
Volume of the
Hydrochloric
Acid/mL (5 mLx3)
Volume of HCl is same during the experiment
and measured by the graduated cylinder.
According to the volume of hydrochloric acid,
diffusion time can be fast.
Amount of Phenol
Red/ mL (5 mL)
Amount of phenol red is same during the
experiment and measured by the graduated
cylinder. If the amount of phenol red change,
the rate of time can be change as well.
Agar Gel Type
The same agar used during the experiment. If
the agar gel different from each other, time of
the diffusion can be change.
Height of the Agar
gel/cm (0.4±0.1
cm)
The height of the agar gel did not change
because the same agar used during the
experiment. If the height of the agar gel change,
the rate of diffusion can be change as well.

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MATERIALS
 Agar-agar (5 g)
 Pure Water (250 mL)
 Phenol Red (5 mL)
 Hydrochloric Acid (15 mL) (d=1.19 g cm-3
)
 100 mL Graduated Cylinder (±0.5)
 250 mL Erlenmeyer (±5)
 250 mL Beaker (±5)
 100 mL Beaker (±0.5) (x3)
 30 cm Ruler (±0.1)
 Petri Dishes (x2)
 Dropper (±0.25)
 Stirring Rod
 Scale
 Heater
 Cutter
 Chronometer (±0.05)
 Thermometer (±0.1)
PROCEDURE
i. 5 g agar-agar and 250 mL is put pure water into the Erlenmeyer and mixed.
ii. While heating the solution, blended them at the same time.
iii. After boiling, 5 mL phenol red is added and mixed.
iv. The solution in petri dishes is spilled equally.
v. When the solution become solid, the gel is cut shape of squares that sides are 1, 2
and 3 cm. (Area of the square which is side 1= 1 cm2
, Area of the square which is
side 2= 4 cm2
, Area of the square which is side 3 =9 cm2
)
vi. 5 mL hydrochloric acid is put in the three 100 mL beakers. (Safety: Wear
disposable plastic gloves to protect your hand.)
vii. The gel squares are put in each beaker. Chronometer is started, until the gel being
colorless.
viii. The records are taken.
ix. The experiment is repeated for more 4 times.

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PRESENTATION OF DATA METHOD
The data can be shown by the table and graph. Raw data include 5 of the trials and uncertainty
of the chronometer (±0.05) and ruler (±0.1). According to the raw data table, take the avarage
of the trials and make a processing data table. Sketch a best fit line graph according to the
processing data table.
DATA COLLECTION AND PROCESSING
Quantitative Data:
Table 2: The Rate of Change in Diffusion According to the Surface Area of Agar Gel
Surface Time/s (±0.05)
Area/ cm2
Trial 1 Trial 2 Trial 3 Trial 4 Trial 5
(±0.01)
1 37.54 32.67 33.98 42.16 45.73
4 39.07 37.53 34.92 37.31 30.42
9 29.26 25.44 26.75 25.39 21.83
Calculation:
Take the average of the all values for the 1 cm2
agar solution.
(37.54 + 32.67 + 33.98 + 42.16 + 45.73)
5
= 38.42 ± 1
Take the average of the all values for the 4 cm2
agar solution.
(39.07 + 37.53 + 34.92 + 37.31 + 30.42)
5
= 35.85 ± 1
Take the average of the all values for the 9 cm2
agar solution.
(29.26 + 25.44 + 26.75 + 25.39 + 21.83)
5
= 25.73 ± 1
Table 3: Average of Rate of Change in Diffusion According to the Surface Area of Agar Gel

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y = -1,6309x + 40,944
R² = 0,9652
20
25
30
35
40
45
0 1 2 3 4 5 6 7 8 9 10
Time/s(±0.05)
Surface Area/ cm2 (±0.01)
Surface Time/s (±0.05)
Area/
cm2 Average Rate
of Time
(±0.01)
1 38.42
4 35.85
9 25.73
Graph 1: Rate of Diffusion According to the Surface Area of the Agar Gel
Error bars measured by the uncertanity of the time (chronometer) which is ±0.05s and 30 cm
ruler which is uncertanity of ±0.1.
Qualitative Data:
1. When the solution was heated, the color turned soft yellow.
2. When the solution came to its boiling point, phenol red was added and the solution
turned red.
3. At the end of the experiment the pink color changed to yellow.
CONCLUSION

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This experiment investigates the relationship between surface area and diffusion rate. As
hypothesis refers to if the surface area of the solution increases, time taken for the diffusion
increases.
The agar gel squares were put in the beaker and hydrochloric acid was dropped on them. The
color changed and turned into soft yellow. At that ending point, the chronometer was stopped
and the data recorded. Consequently, the data is as follows:
According to Table 2 and Table 3, the diffusion rate is affected by the surface area of the cell.
For the surface area of the 1 cm2
agar solution, the time taken was measured 37.54s, 32.67s,
33.98s, 42.16s and 45.73s. Average rate of time for the 1 cm2
agar solution is 38.42s. In trial 5
(maximum value of the rate of the diffusion) and trial 2 (minimum value of the rate of the
diffusion) difference between times is 13.06s and it affected the mean average rate of the
diffusion.
For the surface area of the 4 cm2
agar solution, the time taken was measured 39.07s, 37.53s,
34.92s, 37.31s and 30.42s. Average rate of time for the 4 cm2
agar solution is 35.85s. In the
trial 1 and trial 5 difference between times is 8.65s.
For the surface area of the 9 cm2
agar solution, the time taken was measured 29.26s, 25.44s,
26.75s, 25.39s and 21.83s. Average rate of time for the 9 cm2
agar solution is 25.73s. In the
trial 1 and trial 5 difference between times is 8.43s.
The order of the average time is 38.42s, 35.85s and 25.73s respectively. It means that the
order of the time of diffusion rate is 9 cm2
, 4 cm2
and 1 cm2
respectively, as shown in the
Graph 1. It means that diffusion time rate of 1 cm2
agar solution is slower than the 9 cm2
agar
solution.
The anomalous data of this experiment is 21.83 where it is in the 5th
trial of the 9 cm2
agar
gels. It can be caused of the observation or color change. Other data close to each other.

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This experiment is needed to be compared with another design experiment made by the
student from İhsan Doğramacı Foundation Bilkent Erzurum Laboratory School, Rabia
Hizarci, to be able to find the precise values. “As the graphs show, as the surface area and
volume ratio increases, time taken for diffusion to be completed decreases.” (Hizarci, 2012,
pg. 4) This experiment provides that experiment hypothesis and data are supported.
According to the observations (qualitative data), Table 1, Graph 1 and the experiment done
by Rabia Hizarci, color change is faster in the 9 cm2
of the agar solution. Thus, results support
the hypothesis and the experiment results are reliable.
This investigation can be improved by the new investigations such as volume of the agar gels
and rate of diffusion. The height of the agar gels can affect the rate of diffusion. Another
investigation to improve this experiment is volume, surface area and diffusion rate at the same
experiment.
When the gel interacted with air, the color of the gel turned yellow. It could also be the effect
of the agar gel. Color change cannot be very scientific method for the measuring the rate of
the time taken during the diffusion process, so this can caused by the large amount of time
difference. For that reason, it can be used calorimeter and color change measured more
scientific. Since the results depend on the observation, the data could be affected as well.
Another problem caused the time difference can be the surface area of the agar gel because
when the observing area increases, the observation get impossible to observe. According to
the differences it can be said that difference between the times is less in 9 cm2
.
The experiment can be developed by the using large surface area of the agar gel for instance
4x4, 5x5, 6x6 etc. If the experiment could be repeated more, the values could be more
reliable. Each agar gels placed in the beaker at the same time. The time taken records were
same for all gels. When one of the gel recording, the chronometer did not stop. It was caused
time difference between all agar gels. Agar gels can be put in the beaker different time, then

9. Koz 9
time difference decreases. Error bars can be influenced by the errors of the chronometer and
ruler. It is also caused the large amount of difference between the trails. The range of the
surface area is 1 cm but it is diffucult to observe the color change that is why the range of the
surface area can be increse. For instance, the range between surface area can be 2 cm or 3 cm,
so the agar gel need to be cut 1x1, 3x3, 5x5 or 1x1, 4x4, 6x6. Thus, the observation can be
more easier than to 1x1, 2x2, 3x3.
REFERENCES
Allot, A. (2007) Biology for the IB diploma standard and higher level. Great Clarendon
Street, Oxford: Oxford Press.
Hizarci, R. (2012) Experiment: size-shape and diffusion. Erzurum. Turkey: İhsan Doğramacı
Foundation Bilkent Erzurum Laboratory School. Retrieved from
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0CD4QFjAE&url=http%3A%2F%2Fobelrabiahizarci.files.wordpress.com%2F2012%2F05%
2Fsize-shape-and-diffusion-lab-
report.docx&ei=GDOiUuf8A9SjhgfosIHYCA&usg=AFQjCNFj0xkM2JOHeijpOSqXwXmS
FFygsA&bvm=bv.57752919,d.ZG4>
Hong T. (Seung Mo Hong). (August 15, 2010) How will changing the surface area by
changing the volume, affect the rate of diffusion of sodium chloride across a visking tube,
measured using a conductivity probe? No city of publication. Retrieved from
<http://www.slideshare.net/wkkok1957/effect-of-surface-area-to-volume-ratio-on-the-
diffusion-on-sodium-chloride-from-dialysis-tubing >