Is a plastic sandwich bag selectively permeable?
Today you will be investigating whether or not a plastic sandwich bag is selectively permeable. We can figure this out by
using iodine, which is a known indicator for starch. An indicator is a substance that changes color in the presence of
another specific substance. When iodine comes in contact with starch it turns the solution a dark purple color.
Procedure:
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Fill a plastic sandwich bag with 25ml of the iodine solution and tape the bag closed.
Fill a plastic cup with 25ml of the cornstarch solution.
Place the bag of iodine solution in the cup so the solution is submerged in the cornstarch solution.
Fill a plastic sandwich bag with 25ml of the starch solution and tape the bag closed.
Fill a plastic cup with 25ml of the iodine solution.
Place the bag of cornstarch solution in the cup so the solution is submerged in the iodine solution.
Record your initial observations in table 1.
Let the solutions sit for ½ hour and record your final observations in table 1.
Pour your solutions into the sink, throw away your bags and rinse out your cups.
Table 1.
Initial color
Final color
Iodine solution in bag
Cornstarch solution in cup
Iodine solution in cup
Cornstarch solution in bag
Answer the following questions
1. Based on your observations, is a plastic sandwich bag permeable?
2. Is the plastic sandwich bag permeable to both solutions?
a. Explain how you know.
3. Why can the iodine solution move through the bag and not the starch solution?
4. Explain what the phrase selectively permeable means.