Handle a flask heated in a microwave
One minute or until clear, out with a mitt, and cool until your palm agrees. Learn why the clock is not the endpoint and why hot glass looks exactly like cold glass.
- Hot glass looks like cold glass: There is no color change and no steam coming off a closed flask to warn you. The only reliable information is knowing what has just happened to it.
- An endpoint is a condition, not a countdown: When a protocol says a time or a condition, the condition is the real instruction and the time is an estimate of how long the condition usually takes.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Now use the second check, the one your own hand performs.
The mixture goes clear at forty seconds. Should the group run the microwave to the full minute?
Reviewed- A.Yes, because extra heating makes the gel set faster
- B.No, because a microwave should never run for a full minute
- C.No, because the visible endpoint has already been reached
- D.Yes, because the stated time is the instruction
Show the worked solution ▾
Answer: C. No, because the visible endpoint has already been reached
- Step 1: Find the endpoint in the wording: The step says one minute or until clear, so it offers two ways to stop and one of them has arrived.
- Step 2: Ask what more heating would add: Nothing is left to dissolve, so the extra twenty seconds only boils water away.
Why it's right: The step offers a time or a condition, and the condition has been met. Continuing does nothing except boil off water that was measured into the flask on purpose.
- A: Setting is controlled by cooling, not by extra boiling, and a mixture that has lost water is more concentrated rather than better behaved.
- B: A minute is a perfectly reasonable heating time. It is the wrong stopping rule here only because the mixture got there sooner.
- D: The word or in that step exists to let the condition finish the job early. Treating the time as fixed ignores half the instruction.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
A group is behind and wants to pour while the flask is still too hot to hold. What is the strongest argument against it?
Reviewed- A.Hot buffer stops agarose from ever setting
- B.The gel will be the wrong color if it is poured hot
- C.The mixture will not pour smoothly while it is hot
- D.The protocol names a hand check that has not been passed
Show the worked solution ▾
Answer: D. The protocol names a hand check that has not been passed
- Step 1: Find the instruction: The protocol says to wait until it is comfortable to hold in the palm.
- Step 2: Ask what that check is standing in for: It is the group's only measure of how hot the flask is, and skipping it means pouring blind.
Why it's right: The protocol gives one check for this stage and it is the hand. Skipping it means pouring with no idea how hot the mixture is, next to a tray, tape and a comb that nobody has tested against boiling liquid.
- A: Agarose sets as it cools whether it went into the tray hot or warm, so this overstates the consequence and misses the real one.
- B: The color of the finished gel is not what this wait is about, and a stain has its own separate step.
- C: Hot agarose actually pours more freely than cooler agarose, so the pouring itself is not what argues against this.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A student uses the cooling wait to label bags and set up the tray, which is exactly what the protocol schedules into that gap.
Fill these in as you work through the lesson.
- Endpoint (the condition that says stop):
- Clear (no grains or cloudiness left):
- Mitt (what goes between your hand and hot glass):
- Boil over (the mixture climbing out of the flask):
Heat for about one minute or until the mixture is . Take the flask out with a and set it down rather than carrying it around. Wait until it is comfortable to hold in your before pouring.
- Explain what you are looking for when the protocol says until clear.
- Describe what boiling for longer than needed takes out of the flask.
- Say why a flask that has stopped bubbling is not necessarily safe to grab.
You start the microwave and watch through the door. At forty seconds the last of the cloudiness disappears and the liquid is clear. That is the endpoint, so you stop there rather than running to a minute. Mitt on, flask out, set it on the lab table, and leave it until your palm says it is ready.