Label and store a cast gel between periods
Both bags carry the same two facts. The plastic one keeps the water in, the paper one keeps the light out, and the same pair of materials is wrong somewhere else.
- A label you cannot see is not a label: Once one bag is inside another, only the outer one is readable. Students label the item and stop, and then somebody has to open a package to find out what it is.
- Materials have properties, not rules: Paper lets air through and light does not pass it. Plastic seals and light passes it. Neither is the right answer on its own until you know what you are protecting against.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Give each bag its job, and notice that neither one could do the other's.
A group runs out of paper bags and seals their gel in plastic only, leaving it on the counter under the room lights. Which protection have they lost?
Reviewed- A.The gel will be crushed by other bags
- B.The gel will dry out overnight
- C.The gel will lose its class period label
- D.The gel will be exposed to light all night
Show the worked solution ▾
Answer: D. The gel will be exposed to light all night
- Step 1: List what each bag was doing: One seals, and one is the opaque one.
- Step 2: Remove one and see what is missing: The plastic bag is still sealing. The thing nothing is doing now is blocking light.
Why it's right: The plastic bag is still sealing, so moisture is fine. What has gone is the opaque layer, and a stained gel sitting under room lights all night has nothing between it and them.
- A: Crushing is a real hazard on a crowded counter and it is not what the paper bag was there for, and paper would not prevent it.
- B: Drying is the plastic bag's job and that bag is still on, so this protection is the one they kept.
- C: The label is written on the plastic bag as well, so the identification survives the missing paper bag.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
A group puts their gel loose in the paper bag and seals the empty plastic bag inside it. What is wrong with this arrangement?
Reviewed- A.The gel can dry through the paper, which does not seal
- B.The plastic bag will trap air and crush the gel
- C.The paper bag cannot be folded once a gel is inside it
- D.Nothing, since both bags are still around the gel
Show the worked solution ▾
Answer: A. The gel can dry through the paper, which does not seal
- Step 1: Ask which bag is touching the gel: The paper one, and paper lets air and moisture through.
- Step 2: Ask what the sealed bag is protecting: Nothing, since it is empty.
Why it's right: The layer touching the gel is the one that decides whether moisture can leave, and paper lets it through. The sealing bag is sealing nothing but air, so the slab is drying inside two bags.
- B: A sealed bag of air is harmless. The problem is not what the plastic bag contains, it is that the gel is not inside it.
- C: A paper bag folds perfectly well with a gel inside it, which is exactly what the protocol asks for at the end.
- D: Being surrounded is not the point. What each layer is doing at the surface of the gel is the whole question.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A student can say which bag is doing which job, so a missing bag becomes a known risk rather than a shrug.
Fill these in as you work through the lesson.
- Class period and table number (identifies the gel without naming anyone):
- Opaque (light does not pass through it):
- Sealed (nothing gets in or out, including water vapor):
- Breathable (air and moisture can pass through):
Label bags with the class and the number. The gel is sealed inside the bag, and that goes inside the bag before it is held overnight.
- Explain why the inner bag is labeled when nobody can read it through the outer one.
- Describe what would happen to a gel left on the counter with no bag at all.
- Give a case where sealing something in plastic would be the wrong choice.
Your gel has set. Write your class period and table number on the plastic bag and the same two facts on the paper bag. Put the gel in the plastic, seal it, slide the sealed bag into the paper one, fold the top over, and put it on the side counter for tomorrow.