Australia's Science Forum

Hydrogen Carbonate indicator solution.. the one used to indicate the presence or absence of CO2

Anyone know how to make it/or have a prac using the coloured indicator?

Thanks

If you mean to test for the presence or absence of CO2 & O2 in photosynth & respiration, I use the bromothymol blue-phenol red combination.

Stock bromo blue
Dissolve 0.5g in 0.35ml 2M NaOH & make up to 1L
Stock phenol red
Dissolve 1g in 30ml 0.1M NaOH & make up to 1L

Indicator
Add 4ml bromo blue stock solution to 20ml phenol red stock solution & make up to 2L
This should give you a pale reddish solution. I've found having it quite diluted helps the pond weed & snails survival rates better.
The presence of CO2 turns it orange/yellow, the presence of O2 turns it pink/purple.
Because the pH of the water you use may be different, you might need to tweak the solution with acid or base to end up with the reddish colour.
Sometimes when I make it up it ends up a bit purple so I add a bit of HCl.

If you mean just the bromothymol blue to test for expired CO2 that the kids breathe with the effect of exercise prac then I use this recipe...

Stock bromo blue
Dissolve 1g in 16ml 0.1M NaOH & make up to 1L

Dilute 25ml / L for class use (& add a few drops of NaOH if the diluted solutions ends up a bit green)

Which prac do you want a copy of? I can send you either depending on what you're after

Cheers,

Thanks Binibadgi
This is exactly what I need!

oops!

Bindibadgi

I forgot to add. I would love a copy of the pracs that you use.
Thinking of an animal (insect respiration), a plant one, and a combination of the two, in sealed tubes. If you have any other good ones I can have those too!

Thanks

Here are our Effect of Exercise & Photosynth & Respiration Pracs

Thank You Bindibadgi

Very grateful