Mix a working disinfectant solution
A 10 percent bleach solution is something you make, not something you pour. Learn the dilution, why it is made fresh, and the one thing it must never meet.
- A percentage names a ratio: Ten percent means one part of the thing in ten parts of the finished mixture. It is a recipe, not a brand of bleach.
- A made-up solution has an age: The strength you mixed is not the strength you will have next month. Anything you dilute deserves a date on it.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Now handle an unlabelled bottle, and the one combination that is genuinely dangerous.
A group finds a squirt bottle of cloudy liquid with no label and no date. What should they assume about it?
Reviewed- A.That it was made up this morning, since that is when the room was set up
- B.That it is fine, because bleach is bleach
- C.Its strength and age are unknown, so it should not be relied on here
- D.That it will be stronger than it should be, because water evaporates off
Show the worked solution ▾
Answer: C. Its strength and age are unknown, so it should not be relied on here
- Step 1: List what the bottle tells you: Nothing. There is no label and no date.
- Step 2: Ask what the job needs: A disinfectant of known identity and known strength.
Why it's right: You cannot confirm what is in it or how old it is, and both of those decide whether it will do the job. A disinfectant you cannot vouch for is not a disinfectant, it is a bottle of liquid.
- A: The room being set up this morning is a guess about the bottle, and guessing is exactly what a date on a label removes.
- B: You do not know that it is bleach. An unlabelled bottle could hold anything somebody poured into it.
- D: Water can evaporate from an open container, and that does not tell you what was in it to begin with.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
Why is a bleach solution never combined with another cleaning product?
Reviewed- A.Mixing makes the bleach much less effective than it would be on its own
- B.Mixing products voids whatever guarantee the manufacturer gives
- C.Combined with ammonia or with an acid, bleach releases toxic gases
- D.It leaves streaks that are hard to shift off a laboratory bench
Show the worked solution ▾
Answer: C. Combined with ammonia or with an acid, bleach releases toxic gases
- Step 1: Ask what the risk is: Not a poor clean. A chemical reaction that puts gas into the room.
- Step 2: Ask who it reaches: Everyone in the room, not just the person holding the bottle.
Why it's right: This is not a performance rule, it is a safety rule. Bleach meeting an ammonia based cleaner or an acid produces toxic gas, and that reaches everybody in the room within seconds.
- A: Some combinations do weaken the bleach, and a weaker clean is the least of the problems with mixing.
- B: Warranties are not a laboratory safety consideration and would not apply to a bench cleaning product anyway.
- D: Streaking is a cosmetic complaint and would never be a reason to write a rule this firmly.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A student who finds an unlabelled bottle sets it aside and asks rather than spraying with it.
Fill these in as you work through the lesson.
- Working solution (the diluted version you actually use):
- 10 percent (one part in ten of the finished mixture):
- Fresh (made the day it is used):
- Contact time (how long a disinfectant has to stay wet to work):
A 10 percent bleach solution is one part bleach to parts water. Make it , put a label and a on the container, and never combine bleach with product.
- Say what 10 percent means as a recipe.
- Explain why a working solution gets a date.
- State what must never be added to bleach.
The squirt bottle on your bench says 10 percent bleach and carries today's date. You know what is in it, you know how old it is, and you know it has not been topped up with anything else.