Chad Prescod
10/7/2010
Biology
Investigating the Diffusion of Ions
Introduction:
For cells to survive, they must always transfer their ions, gases, nutrients and wastes with their
environment. They transfer these elements at the cell’s surface. In this lab you will use bouillon cubes,
which has a high salt content, as models of ions diffusion in water. You will observe how the rate of
diffusion is affected by the addition of increasing amounts of bouillon cubes. When the bouillon cubes
are placed in distilled water, they will begin to dissolve, releasing sodium and chloride ions. The
solution’s conductivity, measured by a Conductivity Probe, is proportional to the ions concentration in
the solution after diffusing from cubes.
Research Question:
How is the rate of ions exchange affected by increase in the concentration of ions?
Materials:

Data Logger

Conductivity probe

Distilled Water

Three (3) 400 ml beakers

Bouillon cubes

Utility clamp

Ring stand

Computer
Procedure:
1. Set up the utility clamp, conductivity probe, and ring stand shown in Fig.1.
2. Set selector switch on the conductivity probe to the 0- 20,000 µS/cm ranges.
3. Change the data collection rate to 0.5 samples second and data collection length to 360
seconds.
4. Pour 200 ml of distilled water into the 400 beaker. Position the probe in the water 3 cm from
the bottom of the beaker close to one end of the beaker.
5. Place one solid bouillon cube in the beaker furthest away from the probe and start data
collection. Do not stir the solution.
6. After the time has run its course, analyze the graph to determine the rate of ions exchange.
a) Examine the graph and identify the most linear region.
b) Highlight those data points
c) Select linear fit under analyze menu.
d) Record the slope, m, as the rate of ion exchange
7. Rinse the conductivity probe thoroughly
8. Repeat with an additional two (2) beakers of the same setup.
9. Rinse the conductivity probe ad beaker thoroughly. Dry the beaker and probe using a paper
towel.
10. Repeat steps 4- 9 for 2 bouillon cubes placed in the same area.
Grou
1 cube µs/cm/s
2cubes µs/cm/s
3cubes µs/cm/s
p1:
Group 1
161.1
198.9
256
Chad,
Group 2
129.1
185
228.0
Nick
Group 3
132.7
215.5
233.1
Joe
Diagram:
Group 2- Caitlin, Zayne and Chloe
Group 3- Penny and Ebony
300
bouillon cube test
250
200
Group 1
150
Group 2
Group 3
100
50
0
1 cube µs/cm/s
2cubes µs/cm/s
3cubes µs/cm/s
Limitation:
Due to the fact that there were different groups, and the experiment was done in different
environments. The results and how the experiment was done, although following the instructions may
have affected the outcome.
Conclusion:
By the data of the experiment, it is safe to say the greater the amount of bouillon cubes, the more it
affects how fast the rate of ion exchange to the concentration of ions. This was provided by the single
bouillon cubes which quickly diffused into water because there is not a lot for a single bouillon cube to
pass through. With the two bouillon cubes, the process took longer then before. The water had more
content of the bouillon cubes to breakdown. The two bouillon cubes was 198.9 µs/cms/s unlike the
single bouillon cube which was 161.1 µs/cms/s. The experiment continued the µs/cm/s began to
increase along with the time it took for the bouillon cubes to diffuse into the water. The bouillon cubes
increased the diffusion process and therefore the conductivity increases.