Is it possible to make an accurate DIY Co2 Test Kit?

[Joe]

Hi people,

Is it actually possible to make a DIY Co2 test kit? I really need to get these tests done for my experiment at school, so I just wondered if there is some cheap chemical that I can buy that will react with the amount of co2 in my aquarium?

Joe

[Joshlikesfish]

The test kits are only like $20 on TM?

I know you can test CO2 with limewater

[DubbieBoy]

With any degree of accuracy? No.

Most CO2 tests are merely pH tests; CO2 alters pH in a KH dependant manner.

Even then it's not quantitative. Maybe you could do something with a homemade drop checker, some pH indicator dye and a 4dKH standard solution; it would allow you to visually distinguish low, medium and high CO2 concentrations cheaply. How would you be supplying the CO2 to your experiment?

[Cricketman]

limewater solution of a known molar concentration, added until precipitate is formed in a titration??

Make lime water by getting calcium hydroxide should be easy to get hold of some in the science lab.) and adding it to de-ionised water. distilled water won't work, it will still contain alot of dissolved solids that would interfere with the test.

Calcium should be removed by de-ionisation process, so the only Ca you add is from the lime. D.I water should be available from any laboratory and your school should have a supply or be able to obtain some. By adding the lime slowly, and using measured spoonfuls until you cannot dissolve any more, you can figure out exactly the concentraion of the calcium hydroxide (lime) in the water. By adding this drop-wise to a sample of your tank water, and watching for precipitate (the calcium carbonate) you know exactly how much lime you have added to form the precipitate, and therefore exactly how much CO2 was in your starting sample.

heres the equation:

Ca(OH)2 (aq) + CO2 (g) CaCO3 (s) + H2O (l)

There probably are holes in this theory, but i only just woke up. leniancy please.... 8)