Activity to demonstrate the disinfectant action of chlorine for young (12-16)

[Markos]

Hello,

I'm organizing a citizen science course with diy activities about water
for young people aged between 12 and 16 years old.

I want to include an activity to demonstrate the disinfectant action of
chlorine, and I need to find an activity that uses affordable materials
and culture media and a protocol that is easy for participants to
replicate with kitchen utensils.

But as a Chemist I ask a help to suggest examples on web so I can save
time searching on Google.

Thanks,

Markos

www.c2o.pro.br

[Simon Quellen Field]

It is fairly easy to show the activity of yeast in a sugar water solution.

Add bleach, and the bubbles stop.

I suspect bubbling chlorine gas through it would have the same effect, but that is not something I would try with twelve-year-olds.

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[Kit Martens]

you could also use kitchen agar, nutritional yeast, salt, and tryptone (if you can source it) to make some LB plates - just mix everything together and autoclave it, pour some plates and store them in the fridge until you're ready to use them. Give the kids each three plates. Have the kids breathe on or touch two of them, and then add a teaspoon of bleach to one of the two. in a day you'll be able to see colonies on the plate with no bleach, and no colonies (hopefully) on the plate with bleach. It's a little more involved than the yeast version Simon suggested, but it might be a bit more engaging - it lets them go through an experiment and record results - plus get some exposure to agar plates - which are just a lot of fun and the colonies from just air and hands often end up being pretty and colourful.

[Tom De Medts]

All good answers already. Before I share my suggestion / protocol, can you reply back with 2 details:

1. No. of participants (maximum expected), and

2. Your maximum budget.

[Markos]

Hi Kit,

Please any recipe with the amount? How many grams of each component?

I don't have an autoclave so I would use a pressure cooker.

Could I use whey protein instead of tryptone?

Thanks,

Markos

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[Markos]

Hi Tom,

4 to 6 participants at a time because space is small

US$10,00 for each group of 4 to 6 participants

The idea is to use scrap and buy only what is strictly necessary, such as agar (for edible use).

Thanks,

Markos

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[Nathan McCorkle]

Will you be able to have a microscope available, or maybe the projection microscope that shines a laser through a hanging droplet? I wonder if you could find a yeast cell, then add some bleach and watch it dissolve. 

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-Nathan

[Markos]

Hi Nathan,

You suggest this type of microscope?

https://mad-science.wonderhowto.com/how-to/build-your-own-projection-microscope-with-syringe-laser-pointer-and-drop-water-0138420/

https://makezine.com/projects/laser-projection-microscope/

Thanks,

Markos

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[Tom De Medts]

Here is my suggested protocol #1:

1. Allow bread to sit outside and become infected with mold (type of fungus)

2. Take 1 sample of this mold (some of them can be very nasty to human health if mold spores i.e. dust, is inhaled, especially by immuno compromised individuals)

3. treat this mold sample (dust) for either different amounts of times (30 sec, 1 min, 5min, 10min, 30min) and / or different concentrations (undiluted commercial bleach, and 5 serial dilutions  with dilution factor of 2 each time , so 2, 4, 8, 16, 32 would be the dilution factor)

4. Take these treated mold powder samples, and put them on a new slice of bread, and leave out

5. As a control experiment, leave out an uninoculated slice of bread

6. Expected results: No growth or slower (RE)growth of mold when it has been treated for longer and / or with more concentrated bleach

This suggested protocol obviates the need for LB medium or plates etc etc
And it is perhaps way more intuitive to understand, especially for really young participants or those with no scientific bent of mind, yet.

Because things are less controlled i.e leaving bread outside is not the most controlled experiment, explaining variations in results between replicated experiments will take some explaining.

Apart from variation in results, you may obtain unexpected results, based on random / (un)lucky events, e.g. the uninoculated bread slice has way more mold, but a different color mold

So on and so forth.

But this protocol should easily fit within your $10 budget for a cohort of 5-10 learners. You would only need to but

commercial bleach - $5

bread - $5

tubes / containers to perform the serial dilution in - borrow from some lab?

pipette to perform the serial dilution with - borrow from some lab?

timer to count minutes of bleach treatment (use watch / smartwatch / computer clock)

Cheers!

TdM

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[Jonathan Cline]

Bonus if this includes buying a McDonalds hamburger and placing it out with the bread; then explaining why the McDonalds food never grows any mold at all, even compared to the bleached control.

[Tom De Medts]

For the sake of all those who eat at McDonalds I hope this is not true. 

 But ROFLMAO! Good one, Jonathan Cline. 😂😆

- TdM

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[Markos]

Hi Tom,

Very cool! :-)

Thanks,

Markos

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[Markos]

Hi Jonathan,

Very good suggestion.

Thanks,

Markos

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