Question

In a dialysis experiment with a dialysis full of glucose/starch solution in a beaker of water (tested starch with iodine)- Which solutes would cross the membrane? Why were these solutes able to cross and not others? Do you have evidence that dialysis occurred? Explain. Do you have evidence that osmosis occurred? Explain. Can dialysis and osmosis occur at the same time? Why or why not?

Answer 1

During this experiment, Glucose will diffuse out of the bag while both water and iodine will diffuse into the bag.

a). Glucose and iodine are the solutes that would cross the membrane.

b). They are smaller in size compared to the other solute, starch. Starch is a complex polymer which is larger in size.

c). Yes. Solutes will move into or out of the dialysis bag causing dialysis, in the direction of low concentration, if size of the molecules is lesser than the pore size of the bag. Here, both iodine and glucose cross the membrane. The solution in dialysis bag will turn deep blue as Iodine will diffuse into it. Iodine will change its color in presence of starch in the bag. In addition, the dialysis buffer in beaker will become very pale orange, indicating the presence of only some iodine in it. Presence of glucose can be checked using Benedict's reagent. It will turn yellow to orange or red in presence of reducing sugars.

d). Yes. The bag will expand and get bigger due to osmosis of water into it. Water will enter into the bag as a result of its osmosis through the semipermeable membrane of the dialysis bag from a less concentrated solution into a more concentrated one.

e). Dialysis and osmosis can occur at the same time. Dialysis is the diffusion of a solute across a selectively permeable membrane and osmosis is the diffusion of a solvents across a selectively permeable membrane. Both theses can continue until an equilibrium is reached on both the sides of the membrane.