Young, A. AP Lab # 1Diffusion and Osmosis

IntroductionDiffusion is the movement of molecules from an area of higher concentration

to an area of lower concentration. The molecules pass across a gradient and have a net change in movement until it reaches its equilibrium. Certain type diffusion is osmosis which is the diffusion of water. The goal of molecules moving along a gradient is to reach equilibrium, which is when the solution and the object placed in the solution are both isotonic. When something is isotonic, it is equal in concentration. This means that the molecules are moving into the object and out of the object into the solution equally. When the solution has a higher concentration than the object has, the solution is hypertonic and the object is hypotonic. Hypertonic has more solute and less water whereas the hypotonic has less solute and more water. The hypotonic solution wants to give water to the hypertonic solution; therefore, the object in the hypertonic solution loses water in attempt to reach equilibrium. When the cell loses water, plasmolysis is occurring because the cell is shrinking due to its loss of water. Water is what typically moves across the membrane because most solutes are too large to move across; they cannot pass through the pores on the membrane.

Water potential is based off of two components: pressure potential and the solute potential. Water potential measures the tendency of water to leave on place in favor of another place. This is when it would move down a water potential gradient. If pressure is increased, the water potential increases. If the solute potential is increased, the water potential is also increased. Water potential is the sum of the pressure potential and the solute potential.

DataTable 1.1

Initial Contents Solution Color Presence of GlucoseInitial Final Initial Final

Bag 15% glucose & 1% Starch

Clear Blue-Purple + +

Beaker H2O & IKI Golden-yellow Golden- yellow - +

Table 1.2 – Dialysis Bag Results: Group DataContents in Dialysis Bag

Initial Mass Final Mass Mass Difference Percent Change in Mass

0.0 M 20.85g 20.2g -0.7 -3.1%0.2 M 20.72g 20.4g -0.3 -1.5%0.4 M 21.09g 24.5g 3.4 16.2%0.6 M 19.97g 21.3g 1.3 6.7%0.8 M 21.64g 23.5g 1.9 8.6%1.0 M 22.27g 27.2g 4.9 22.1%

Table 1.3 – Percent Change in Mass of Dialysis BagsPercent Change in Mass of Dialysis Bags Class

AverageGroup1 Group2 Group3 Group4 Group5 Group6 Group7 Group80.0M -3.1 0 1.8 -0.1 0.5 2.6 4.4 -1.1 0.60.2M -1.5 5.8 6.7 5.0 5.7 7.3 6.3 3.2 4.80.4M 16.2 11.4 14.3 8.9 11.5 11.5 13.8 8.9 12.1

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Young, A. AP Lab # 1Diffusion and Osmosis

0.6M 6.7 14.3 18.8 16.4 16.2 18.3 20.2 13.4 15.50.8M 8.6 17.7 23.7 25.1 25.5 25.2 23.6 21.8 21.41.0M 22.1 32.0 39.7 33.5 39.6 45.0 41.0 27.2 35.0

Table 1.4 – Baby Carrot: Individual DataContents in Beaker Initial Mass Final Mass Mass Diff. % Change in Mass

0.0 M 9.17g 9.1g -0.1 -0.8%0.2 M 12.83g 12.5g -0.3 -2.6%0.4 M 10.36g 9.9g -0.5 -4.4%0.6 M 12.75g 11.3g -1.5 -11.4%0.8 M 13.15g 10.7g -2.5 -18.6%1.0 M 14.39g 11.4g -3.0 -20.2%

Table 1.5 – Baby Carrot: Class DataPercent Change in Mass of Baby Carrots Class

AverageGroup1 Group2 Group3 Group4 Group5 Group6 Group7 Group80.0M -0.8 -1.3 -0.3 0.7 0 2.1 -0.4 0 1.40.2M -2.6 -1.9 -1.5 -0.5 -2.2 -0.6 -2.3 -1.3 -1.60.4M -4.4 -1.9 -3.2 -2.8 -3.9 -2.4 -4.4 -4.4 -3.40.6M -11.4 -8.2 -11.6 -11.6 -8.3 -10.9 -10.8 -10.8 -10.10.8M -18.6 -15.8 -19.0 -16.6 -19.6 -16.0 -18.8 -18.8 -17.51.0M -20.2 -18.4 -21.4 -20.5 -21.3 -20.7 -21.3 -21.3 -20.7

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0 0.2 0.4 0.6 0.8 1 1.20

10203040

Class Average of Percent Change in Mass of Dialysis Bags

Molarity of Solution in Beaker (M)

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Young, A. AP Lab # 1Diffusion and Osmosis

Analysis & Conclusions1. Exercise 1A : Describe and explain the results that were obtained. Explain

HOW we know that each substance was moving where it did (or where it didn’t.)Glucose and starch were in the “cell” and the iodine solution was outside of the cell. The initial color of the “cell” was clear and the initial color of the beaker was golden-yellow due the iodine solution in it. As time elapsed, the “cell” color changed to a bluish-purple color while the beaker color remained the same golden-yellow color. Due to the color change in the bag representing the cell, it shows that the iodine solution came through the pores of the membrane and showed the presence of starch. When tested for glucose, the solution in the beaker tested positive for glucose, thus proving that glucose was small enough to pass through the pores of the membrane on the dialysis bag. The sucrose and the starch were too big to move through

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0 0.2 0.4 0.6 0.8 1 1.2

-25-20-15-10

-505

Class Average Percent Change in Mass of Baby Carrots

Molarity of Solution in Beaker (M)

Perc

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hang

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Mas

s (%

)

0 0.2 0.4 0.6 0.8 1 1.2

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

Percent Change in Mass of Zucchini Cores

Amount of Sucrose Molarity (M)

Perc

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hang

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Young, A. AP Lab # 1Diffusion and Osmosis

the pores of the membrane because they were not found in the beaker solution. The glucose molecules, water molecules, and iodine are small enough to pass through the membranes’ pores.

2. Exercise 1B : Describe and explain the results that were obtained using the dialysis bags in distilled water.The dialysis bags containing different molarity levels of sucrose and weighted. They were then placed in cups of distilled water. After completely immersing the dialysis bags in the distilled water for 30 minutes, the bags were weighted again. The results showed that the difference between the final mass and the initial mass had an increase. The dialysis bags increased in mass, therefore they gained water. The bags were hypertonic to the distilled water, which was hypotonic. The water molecules from the distilled water went into the dialysis bags in attempt to create equilibrium by balancing out the concentration in the bags and the cup. Hypotonic solutions always donate to the hypertonic solution.

3. Exercise 1C : Describe and explain the results that were obtained using the carrots in the varying sucrose solutions.Two carrots were placed in different levels of molarity of sucrose. The carrots were weighted before they were placed in the sucrose solution and then they were left overnight while completely immersed in the solutions. They were then weighted again, and results showed that there was a decrease in mass. This means that the carrots were hypotonic to the solutions, which were hypertonic, they were immersed in. In attempt to reach isotonic and equilibrium, water left the carrot and entered the sucrose solution.

4. Exercise 1D : Describe the results that were obtained in the zucchini core experiment. Explain what these results indicate about the molarity of zucchinis. Identify the molar concentration of the zucchini cores and indicate how you know this.The zucchini cores lost mass throughout the experiment. The higher the sucrose molarity was, the greater the percent change in mass. Like the carrots, the zucchini were hypotonic to the hypertonic solution they were immersed in. Therefore, they lost water in attempt to create equilibrium, making both the zucchini and the solution isotonic. The molar concentration of the zucchini cores is most likely 0.26M because it is at equilibrium when it crosses the X-axis at 0 and it does with the molarity at roughly 0.26M. This is shown in the graph above titled “Percent Change in Mass of Zucchini Cores.”

5. Exercise 1E : Describe and explain the results that were obtained using the onion cells and the salt solution.When the salt solution was added to the onion cells, the onion cells lost water, thus causing them to shrink in the process of plasmolysis, which is the shrinking of the cytoplasm. The cell is hypotonic and the salt solution is hypertonic, so in attempt to reach equilibrium, the water from the cytoplasm leaves the cell and goes to the outer salt solution. The cell wall, however, still holds its shape.

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