A student designed a container to store bleach (sodium hypochlorite solution) and chose a clear PET plastic bottle because it is strong and transparent.
Observations during a 6-week storage test in a sunny window:
- The bleach lost strength faster than expected (less effective cleaning).
- The bottle became slightly yellow and more brittle.
- The same bleach stored in an opaque HDPE bottle kept its strength longer.
Which refinement best matches the evidence?
- Switch to an opaque, bleach-compatible plastic (such as HDPE) or add a UV-blocking/opaque layer to reduce light-driven degradation (correct answer)
- Keep the clear PET bottle but add sugar to the bleach to stabilize it
- Use a thinner PET bottle so less plastic can turn yellow
- Store the bleach at a higher temperature so it reacts faster during cleaning
Explanation: This question tests your ability to use evidence from testing and observations to refine engineering designs by identifying chemical property inadequacies and proposing targeted modifications that address specific problems. Design refinement is the engineering practice of using test results and evidence to improve solutions through iteration: when testing reveals problems (material corrodes, degrades, reacts, fails under conditions), you don't start over completely—instead, you make targeted changes that address the specific issues while preserving aspects that worked well. The key is connecting evidence to refinement: if tests show plastic container cracked after acid exposure (evidence), the refinement must address acid resistance specifically (switch to acid-resistant material or add protective coating), not make random changes. Good refinements are evidence-based (data shows the problem), targeted (fixes specific issue, not everything), and feasible (realistic with available materials/methods). This is how real engineering works—iterative improvement based on testing! Observations during sunny storage show bleach losing strength and PET yellowing/brittling, while opaque HDPE preserved strength, indicating light-driven degradation, so refinement should add opacity or UV protection for compatibility. Choice A proposes an appropriate refinement by targeting the specific chemical property problem identified in test evidence—switching to opaque bleach-compatible plastic or adding UV layer—while maintaining strength. Choice B is wrong because adding sugar doesn't stabilize against light degradation per the evidence, potentially introducing new issues. The evidence-to-refinement process: (1) ANALYZE EVIDENCE: What specific problem does testing reveal? (degradation in light = photo-instability). Be specific about what failed! (2) IDENTIFY CAUSE: What chemical property is inadequate? (PET not UV-resistant for bleach). Connect failure to missing property. (3) TARGET REFINEMENT: What change addresses that specific property inadequacy? (use opaque/UV-blocking material). Refinement must logically fix the identified cause. (4) PRESERVE SUCCESSES: Keep aspects that worked well—don't throw out everything! If strength is good, retain it in new material. You're excelling—keep using evidence!