Which indicator can be used to detect the formation of dissolved carbon dioxide gas in water, CO2(aq)?
CO2(aq) reacts with water to form carbonic acid, H2CO3(aq), which lowers the pH of the water. Bromothymol Blue (BTB) 0.5% aqueous indicator solution (#9447202) works well for detecting the resultant drop in pH. This comes in a 30-mL dropper bottle for easy dispensing. BTB is blue above pH 7 and yellow below pH 6. One drop of 0.5% BTB mixed with 100 to 200 mL of water will give a very light blue colored solution. Upon bubbling CO2 gas through the water, the solution color will change to yellow.
