Lab 6 Diffusion PDF

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Lab 6 Diffusion...

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Diffusion PRE-LAB QUESTIONS 1. A concentration gradient affects the direction that solutes diffuse. Describe how molecules move with respect to concentration.

a. Diffusion is a process in which solute molecules when left to themselves in a solution move from a region of higher concentration to lower concentration, this eventually leads to uniform distribution of that solute molecule in that solution over a period of time.

2. How does the size of a solute affect the rate of diffusion? Consider the size and shape of a molecule in your response.

a. The size of the solute molecule is inversely proportional to the rate of diffusion, so bigger the size of the solute molecule, slower will be the rate of diffusion.

3. Does polarity affect the rate of diffusion? Explain your answer using scientific principles.

a. Polarity of solute has negligible effect on diffusion of the molecule in solvents like water or any other aqueous solutions. But in case of a cell, if the molecule has to pass though cell membrane then at that situation polarity may play an important role towards diffusion of the molecule.

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Diffusion EXPERIMENT 1: DIFFUSION THROUGH A LIQUID Result Tables Table 1: Rate of Diffusion in Corn Syrup Time (sec)

Blue Dye

Red Dye

10

0.7cm = 7mm

1.4cm = 14mm

20

1cm = 10mm

1.5cm = 15mm

30

1.1cm = 11mm

1.7cm = 17mm

40

1.2cm = 12mm

1.8cm = 18mm

50

1.2cm = 12mm

2.0cm = 20mm

60

1.3cm = 13mm

2.1cm = 21mm

70

1.5cm = 15mm

2.3cm = 23mm

80

1.6cm = 16mm

2.5cm = 25mm

90

1.6cm = 16mm

2.5cm = 25mm

100

1.6cm = 16mm

2.6cm = 26mm

110

1.7cm = 17mm

2.6cm = 26mm

120

1.7cm = 17mm

2.6cm = 26mm

Table 2: Speed of Diffusion of Different Molecular Weight Dyes Dye

Molecular Weight

Total Distance Traveled (mm)

Speed of Diffusion (mm/hr)*

Blue Dye

793g/mole

250mm

7500mm/hr

Red Dye

496g/mole

156mm

4680mm/hr

*Multiply the total distance diffused by 30 to get the hourly diffusion rate.

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Diffusion Post-Lab Questions 1. Record your hypothesis from Step 3 here. Be sure to support your hypothesis with evidence. a. The increase in the water temperature increases the rate of diffusion and if the water temperature get decreased rate of diffusion will decreased. b. Potassium permanganate is added in different quantities in the water that show different rates of diffusion. 2. Which dye diffused the fastest? a. The red dye 3. Does the rate of diffusion correspond with the molecular weight of the dye? a. yes 4. Does the rate of diffusion change over time? Why or why not? a. Yes, as the solution reaches equilibrium the rate of diffusion decreases. 5. Examine the graph below. Does it match the data you recorded in Table 2? Explain why or why not. Submit your own plot if necessary.

a) No it doesn’t, the times the, and the diffusion distance do not cohere correctly between the graph and the table

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Diffusion b) No

EXPERIMENT 2: CONCENTRATION GRADIENTS AND MEMBRANE PERMEABILITY Result Tables Table 3: Indicator Reagent Data Indicator

Starch Positive Control (Color)

Starch Negative Control (Color)

Glucose Positive Control (Color)

Glucose Negative Control (Color)

IKI Solution

Dark blue

Light brown

n/a

n/a

Glucose Test Strip

n/a

n/a

green

Yellow

Table 4: Diffusion of Starch and Glucose Over Time Indicator

Dialysis Bag After 1 Hour

Beaker Water After 1 Hour

IKI Solution

from uncolored changed to blue dark color

pale yellow

Glucose Test Strip

yellow

green

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Diffusion

Post-Lab Questions 1. Why is it necessary to have positive and negative controls in this experiment? a. positive and negative controls are very useful because we will be sure that in the solution in the baker there is no traces of glucose before the initiation of the experiment and to know which color have the strip is glucose is present or absent 2. Draw a diagram of the experimental set-up. Use arrows to depict the movement of each substance in the dialysis bag and the beaker.

3. Which substance(s) crossed the dialysis membrane? Support your response with databased evidence. a. Glucose and iodine can pass through the dialysis bag membrane as its molecules are smaller than the pores sizes of the membrane. 4. Which molecules remained inside of the dialysis bag? a. Starch will remind inside the bag and react with iodine turning to dark blue color 5. Did all the molecules diffuse out of the bag into the beaker? Why or why not? a. No starch did not as its molecules are larger than the pore sizes of the dialysis bag membrane

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