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Factors Affecting Diffusion

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Andrew Nguyen

on 11 February 2015

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Transcript of Factors Affecting Diffusion

Experimental Design
3 400 mL beakers
1 10 mL graduated cylinder
a roll of dialysis tubing
disposable pipets,
Lugol Solution,
a 0.06 M starch solution,
deionized water,
a roll of string,
a hot plate,
a bucket of ice,
3 thermometers
3 stopwatches.
4 400 mL beakers
1 10 mL graduated cylinder
disposable pipets
a roll of dialysis tubing
a container of NaCl (table salt)
a roll of string
weigh boats
a gram scale
In the end, we found our hypothesis was reinforced by the data we gathered. The rate of diffusion increased as the osmolarity of the NaCl solution in the beaker increased.

Possible Errors:

Scale did not stabilize correctly, possible due to movement around the table or air from the air vents above. (ie. the difference in the amount of salt in our third trial could be due to this.)
Incomplete dissociation of salt and water could have altered the diffusion rate
Both the initial and final weight of the tubing was affected by the string absorbing water, thus we ran our data in both grams & mL.

Experimental Design
Steps 1:
cut dialysis tubing into multiple 10 cm strips.
Steps 2:
Fill each dialysis tube with 5 mL of deionized water and set them aside in a 400 mL beaker that is filled with deionized water.
Steps 3:
prepare three 10 mOsM NaCl solutions in each of the beakers.
Steps 4:
Afterward, set a timer for 20 mins and put one dialysis tube into each of the three beakers.
Steps 5:
When the time is up, take each dialysis tube and measure it's volume.
Experimental Design
Step 1:
Fill each 10 mL graduated cylinder with 3 mL of 0.06 M starch solution using a disposable pipet
Step 2:
Pour one 3 mL starch solution into each beaker. Dilute each beaker by filling it with DI water until the solution reaches a volume of 75 mL. (yields 2.7 cm distance).
Step 3:
Once the starch has settled, drop one drop of iodine into the middle of a beaker. Start timing when the drop reaches the surface of the beaker solution.
Step 4:
As soon as there is a color change (black-blue) in the starch at the floor of the beaker, stop and record the time.
Step 5:
Repeat steps 1-4 for each solution you prepare, while keeping molarity constant. (ie. A 5 mL of 0.06 M starch solution and a 125 mL solution volume yields a distance of 4.3cm.
7 mL of 0.06 M starch solution and a 175 mL solution volume yields a distance of 5.9 cm).

By doing this, molarity through all solutions remains the same, at 0.0025M

3 300 mL beakers
3 10 mL graduated cylinders
disposable pipets
1 400 mL beaker filled with deionized water
0.06 M starch solution
a bottle of iodine w/ dropper
a stopwatch.
Factors Affecting Diffusion
Temperature is one of the factors that affects diffusion. In diffusion, molecules move from an area of high concentration to an area of low concentration, eventually achieving equilibrium. For example, if the concentration of a solute is higher on one side of a membrane, the molecules will diffuse across the membrane onto the opposite side due to the concentration being lower. Molecules do this through Brownian movement, which is the random movement of molecules within a medium. One of the factors affecting the rate at which molecules move is temperature. As temperature increases, so does the speed at which the molecules move throughout the environment. The same holds true for the opposite direction. Lower temperatures make for slower molecular movement. As molecular motion is affected by temperature, so, too, is diffusion.
As mentioned in our previous experiment, diffusion is the movement of molecules from an area of high concentration to an area of low concentration. Similarly, osmosis is the diffusion of water through a semi-permeable membrane. Water travels from an area of low solute concentration to an area of high solute concentration in an attempt to reach equilibrium. Osmolarity is the number of solute particles per litre of solution. Diffusion rate is affected by the concentration gradient. The greater the difference between two concentrations, the higher the rate of diffusion will be.
There are many factors that affect diffusion as we’ve seen through our previous two experiments. The final one we chose to test is distance. The rate of diffusion is related to distance in the sense that as the distance required by a molecule to travel is increased, so does the time it takes for the molecule to reach its final destination. The factor by which travel time increases is exponential relative to the increase in distance.
For this experiment, our hypothesis is that the rate of diffusion of iodine through the dialysis tubing will increase as the temperature also increases. Diffusion rates at higher temperatures will be greater than those seen at lower temperatures.
Step 1:
fill 2 beakers with 350 mL of deionized
filling two beakers with 350 mL of deionized
water and placing a thermometer in each
Step 2:
Prep each beaker of water for its temperature condition. (1 hot, 1 Rm. Temp., 1 Cold)
Step 3:
Cut multiple 13cm strips of dialysis tubing, tying one end off.
Step 4:
Add 40 drops of Lugol's Solution to each of the beakers and let it mix evenly.
Step 5:
fill each dialysis tube with 4 mL of the 0.06M starch solution and 6 mL of deionized water, then tie it shut.
Step 6:
Drop 1 dialysis tube into each beaker, while starting a timer.

When the starch in the dialysis tubing changes color (black-blue), record the time. You're done!
As osmolarity increases, so does the amount of water transferred across the membrane. As a result, more water will be drawn out of the 0.0 mOsM dialysis tubing as the osmolarity of the NaCl solution on the outside of the tubing is increased.
An average diffusion rate was taken for each of the three osmolarities. Mass over time and volume over time were calculated to show rate of diffusion. 2 mOsM yielded diffusion rates of 0.0236 g/min and 0.0608 mL/min, 10 mOsM had diffusion rates of 0.0386 g/min and 0.0883 mL/min, while 20 mOsM produced diffusion rates of 0.0491 g/min and 0.1125 mL/min. The relationship between osmolarity and rate of diffusion was direct.
As the distance between the surface of the solution and the bottom of the beaker increases, the time it takes for the drop of iodine to reach the floor of the beaker increases as well.
Our results show that diffusion took longer to occur in cold water (the amount of time it takes iodine to initially react with starch), averaging at about 9 minutes 24 seconds, than it did in room temperature and hot water. Hot water also took longer to diffuse than room temperature water. The average time for hot water being 7 minutes 52 seconds while the room temperature water produced an average time of 6 minutes 49 seconds.
In conclusion, we found that our hypothesis was somewhat reinforced in the sense that cold water diffused slower than room temperature water, but was refuted in the sense that hot water also diffused slower than room temperature water.

Possible Errors:
While tying the dialysis tubing it's possible that some starch solution leaked out. As a result, it could have caused the iodine to react faster than intended.
On one trial we forgot to shake the stock starch solution before adding it into our 10mL solution, which changed the concentration gradient compared to the other solutions.
We found that on one trial that dropping the iodine solution directly on the membrane caused an immediate reaction
Higher temperatures than 40℃ produced longer reaction times
We didn't use the same thermometer for each trial, which would have been ideal.
After collecting data for three different distances, we took the average times for each distance and plotted the information onto a graph. The average times for each distance were 3.70 seconds for 2.70 cm, 14.44 seconds for 4.30 cm, and 29.81 seconds for 5.90 cm. A direct relationship between distance and time can be observed from the gathered information.
In this final experiment, we found our data yielded results that reinforced our hypothesis. As the distance between the surface of the solution and the bottom of the beaker increased, the time it took for the iodine to reach one point to the other increased as well.

Possible Errors:
Dropping the iodine at a higher height would have been helpful to allow the person with the stopwatch more time to react to the droplet hitting the surface of the solution.
Any particles of starch floating around in solution may affect diffusion rate; therefore, we suggest one to wait for the starch to fully settle at the bottom of the beaker.
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