Keep the extraction alcohol ice cold
The materials list does not say alcohol. It says alcohol kept ice-cold. Learn what the temperature is buying you and what a warm bottle costs your result.
- A substance can be dissolved or clumped: Dissolved means spread through a liquid and invisible. Clumped means gathered into something you can see and pick up. This extraction is a deliberate move from one state to the other.
- Temperature changes how much stays dissolved: Cooling a mixture usually leaves less dissolved and more settled out. That is the lever this step is pulling, and it is why the bottle sits in ice.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Now read a tube that came out almost empty, and decide what to change.
A group's tube shows almost no white strand. Their buffer and volumes were right, but their alcohol came from a bottle that had sat out since the start of the period. What is the most likely reason?
Reviewed- A.They used more alcohol than the procedure calls for at that step
- B.The alcohol was warm, so more of what they extracted stayed dissolved
- C.Their cheek cells never released any material into the salt solution they rinsed with
- D.The salt solution they rinsed with was made up too weak
Show the worked solution ▾
Answer: B. The alcohol was warm, so more of what they extracted stayed dissolved
- Step 1: List what was the same as everyone else: Buffer, volumes, technique. Those are ruled out.
- Step 2: List what was different: Only the temperature of the alcohol. That is the variable to name.
Why it's right: Everything else matched the groups that got a strand. The one condition that did not match was the temperature of the alcohol, and warm alcohol is exactly the condition that leaves more of the material in solution and less of it visible.
- A: Volume was stated to be correct, and in any case adding extra alcohol does not thin out a strand that has formed.
- C: A rinse that produced nothing at all is possible, but it does not explain why this group differed from the others on one specific handling step.
- D: The salt solution is also stated to have been handled the same way, so it is not the variable that separates this group.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
That group wants to try again. What should they change, and what should they leave alone?
Reviewed- A.Leave the tube on the bench overnight so it has longer to form a strand
- B.Add a second volume of the same bench-temperature alcohol on top of the first, and give it longer to gather
- C.Shake the tube hard after the pour so the two liquids meet everywhere at once
- D.Take the alcohol from the bottle standing in ice and leave the rest of the procedure as written
Show the worked solution ▾
Answer: D. Take the alcohol from the bottle standing in ice and leave the rest of the procedure as written
- Step 1: Name the one thing that went wrong: The temperature of the reagent.
- Step 2: Change only that: Changing several things at once means you will not know which repair worked.
Why it's right: One condition was out of specification, so one condition gets fixed. Taking the alcohol from the ice restores the reagent the procedure asked for and leaves every other step exactly where it was working.
- A: Time is not the limiting factor here, and a tube left open overnight on a bench is not a stored sample.
- B: More of a reagent does not substitute for a reagent in the wrong condition, and the volume was already correct.
- C: Shaking works directly against the next step, which depends on the two liquids staying apart rather than meeting everywhere.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A student whose extraction failed names the reagent condition rather than blaming their own hands.
Fill these in as you work through the lesson.
- Dissolved (spread through the liquid, not visible):
- Precipitate (come out of solution as something solid):
- Ice-cold (a condition in the materials list, not a suggestion):
- Flammable (what 95 percent alcohol is, all day, capped or not):
DNA stays in water and clumps together in . Keeping that alcohol leaves less of the DNA in solution, so more of it gathers where you can see it.
- Say what the crushed ice in the materials list is actually for.
- Describe what a tube looks like when the alcohol was too warm.
- Explain why the stock bottle gets capped between pours.
You pour your 3 mL from the bottle standing in the ice cup, cap the bottle, and set it back in the ice. The alcohol that reaches your tube is as cold as the one that reached the group before you, which is the only way two groups can compare their results.