Lab 1: Diffusion and Osmosis
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measure of free energy of water in a solution
the movement of a solute through a selectively permeable membrane
the presence of glucose will be tested by __.
the presence of starch will be tested by __.
With a bag with glucose and starch placed in a beaker with H2O and IKI, what are the initial and final colors of hte solution?
What is the initial and final presence of glucose?
- Solution color
- Bag: clear/ blue
- Beaker: gold/ no change
- Beaker presence:
- Bag: + +
- Beaker: - +
Which substances are entering the bag and which substances are leaving?
- Entering the bag:
- Water and IKI
- Glucose and water
- Evidence: At first the bag was clear, but since IKI diffused through (IKI and sucrose cause a bluish color), the bag turned blue.
- The beaker had glucose in it as detected by Benedict's solution.
Explain the results you obtained and the concentration differences.
- The bag was clear and then blue. THis is because IKI diffused into the bag because it was less concentrated on that side. Water diffused into and out of the bag, mostly in because of the more negative water potential, and tried to obtain equilibrium.
- Glucose moved out of the bag because it was less concentrated in the beaker nad moved to obtain equilibrium.
- Starch did not move because the membrane pore sizes were too small to allow starch to pass through but were big enough for water, IKI, and glucose to pass.
How could this experiment be modified so that quantitative data could be collected to show that water diffused into the dialysis bag?
We could have weighed the bags in the beginning and end to detect hte change in mass of the bags.
Rank the following from the smallest:
starch, water, membrane pore, glucose, IKI
water, IKI, glucose, membrane, starch
What results would you expect if the experiment started with a glucose and IKIK solution inside the bag and only starch and water outside?
- the inside would remain gold throughout because starch cant pass into the bag.
- the outside would be clear and then would turn blue because IKI passes into the beaker.
If we placed bags with increasing molarity in a beaker of distilled water, what is expected to happen?
- The distilled bag would be isotonic and therefore really no change in mass.
- All other bags would increase in mass, the one with the greatest molarity would have the greatest increase.
How do you calculate percent change in mass?
[(Final- Initial)/ Initial ] x 100
What is the independent variable in the tubing with different molarities bag?
- inde: molarities in bag
- dep: change in mass
Explain the relationship between the change in mass and the molarity of surcrose in the bags.
As the sucrose molarity in each bag increases, a greater change in mass occurs. More water diffuses into the bag with increasing molarity. THe higher the molarity, the higher the % change in mass.
Why did we calculate for percent change in mass rather than using change in mass?
it was more accurate. THe weight of the bags and volumes were not the same, so they correct for differences in the initial bag. It would show greatly the masses increased or decreased.
A dialysis bag is filled with distilled water and placed in a sucrose solution. THe bag's initial mass in 20 g, and its final is 18 g. Calculate the percent change in mass.
- The solution in the beaker would be hyper, hypo, or iso?
- 18-20= -2/ 20 = -.1 x 100= -10%
How do you calculate the molar concentration (the sucrose molarityin which the mass of hte cell does not change)?
where the line crosses the x axis is where equilibrium is reached.
How do you calculate the solute potential - with what equation?
- -1 x concentration x .0831 x (273 + temp)
A 1.0 sugar solution at 22 degrees C under standard atmospheric conditions is: __
-1x 1 x .0831 x (273+ 22) = -24.51
Knowing the solute potential of the solution and knowing that the pressure potential of hte solution is zero allows you to calculate the __ of the solution.
If a potato core is allowed to dehydrate by sitting in the open air, would the water potential of the potato cells decrease or increase?
it would decrease because the water is leaving the cells, causing water potential to decrease. It increases solute potential but decreases water value.
What effect does adding solute have on the cell?
it increases solute potential but decreases water potential; because the outside is more negative, it causes a decrease in the % change in mass of the cells
What is plasmolysis?
hte shrinking of the cytoplasm and pulling away fo the cell membrane in response to being placed in a hypertonic solution
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