Hydrogen carbonate indicator solution

Hydrogen carbonate indicator solution

Can you give me a recipe for Bicarbonate (or Hydrogen carbonate) Indicator solution?

Dissolve 0.2g of thymol blue and 0.1g creosol red in 20 cm3 ethanol.

Weigh out 0.84g of sodium hydrogen carbonate (Analar) and dissolve this in about 900 cm3 of deionised or distilled water.

Add the dye solution to the aqueous salt solution in a 1 litre graduated flask and make up to the 1 litre mark with deionised/distilled water. Take care to exclude all traces of dust and dirt as these have a marked effect on the final colours the indicator will produce.

Working solution:-

Pipette 25 cm3 of the stock solution into a 250 cm3 graduated flask and make up to 250 cm3 with deionised/distilled water.

Equilibration with atmospheric air:-

Before the reagent can be used, it must be allowed to reach equilibrium with the CO2 in the atmosphere. Bubble air through the solution using a fish-tank bubbler. The air must come from outside the laboratory as the solution is very sensitive to small changes in CO2. The indicator should appear deep red in the bottle and orange red when viewed in 16mm test-tubes.

In UK, it is possible to buy this ready-made.

(add sodium hydroxide to have a pink colour to show the kids)