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Comparing Selective Membranes in a Model Wash 4 questions
Comparing Selective Membranes in a Model Wash
Base your answers on the information provided and your knowledge of chemistry. Use the 2025 Chemistry Reference Tables as needed.
A classroom model uses a membrane to wash dissolved salt out of a solution containing a large colored polymer. It measures the percentage of each solute that crosses into fresh water. A membrane is acceptable if at least 80% of the salt crosses and at most 5% of the polymer crosses during the test.
| Membrane | Salt crossing (%) | Polymer crossing (%) |
|---|---|---|
| A | 91 | 12 |
| B | 85 | 3 |
| C | 65 | 1 |
Question 1
Which membrane meets both requirements?
- A only
- B only
- C only
- B and C
Question 2
Give a particle-size explanation for why a membrane could pass many dissolved ions but little of the polymer.
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A student tests a used piece of B and finds 75% salt crossing and 2% polymer crossing. The class wants to know whether use caused the change or whether this piece of B already performed differently when new.
Question 3
Describe a comparison that would better isolate the effect of repeated use on B. State what to measure.
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Question 4
A student says the used piece still meets the requirements because it loses less polymer. Evaluate that claim using both limits.
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