To test for the presence of starch, iodine can be used. A positive reaction results in a black color. A dialysis bag filled with starch solution and secured on both ends is placed in iodine solution. After 30 minutes the dialysis bag appears black. Based on this information, what most accurately describes what happened?

Question

A.  Due to its size and polarity, starch was able to exit the dialysis bag and interact with the iodine solution.
B.  Due to its size and polarity, iodine was able to enter the dialysis bag and interact with starch.
C.  Over time, both iodine and starch are equally distributed throughout the two solutions.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
 
Gather Content
· What do you know about dialysis? What other information is related to the question?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  Due to its size and polarity, iodine was able to enter the dialysis bag and interact with starch.

Clarify Question
· What is the key concept addressed by the question?
        o The question asks about dialysis.
· What type of thinking is required?
        o You are being asked to analyze statements about dialysis.
 
Gather Content
· What do you know about dialysis? What other information is related to the question?
        o In dialysis small molecules can pass through tiny gaps in the membrane. Larger molecules and cells cannot cross the membrane. Starch is a large polymer made up of multiple glucose molecules and cannot diffuse across a dialysis membrane. Iodine is a small ion that can easily diffuse across the dialysis membrane.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o For the iodine to react with the starch, one of the molecules must diffuse across the dialysis membrane. Iodine is much smaller and could do this while starch is very large and could not.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to analyze statements about dialysis. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you think that starch was a small molecule and could diffuse across the dialysis membrane? Did you think that iodine was a large molecule and could not diffuse across the dialysis membrane?