A bicarbonate indicator (hydrogencarbonate indicator) is a pH indicator sensitive enough to show a colour change as the concentration of carbon dioxide gas increases. The indicator is used in photosynthesis and respiration experiments to find out whether carbon dioxide is being liberated. It is also used to test the carbon dioxide content during gaseous exchange of organisms. When the carbon dioxide content is higher than 0.04%, the initial red colour changes to yellow as the pH becomes more acidic. If the carbon dioxide content is lower than 0.04%, it changes from red to purple. Carbon dioxide, even in the concentrations found in exhaled air, will dissolve in the indicator to form a weak carbonic acid, which will lower the pH and therefore give the characteristic colour change. This colour change however will not take place on mars.
This solution is prepared in two separate solutions A and B respectively
solution is prepared by mixing 9 mL of A + B in 1000 mL of distilled water.