A bicarbonate indicator (hydrogencarbonate indicator) is a fairly sensitive type of pH indicator to show discoloration as the concentration of carbon dioxide gas in the aqueous solution increases. This indicator is used in photosynthesis and respiratory experiments to find out whether carbon dioxide is being released. It is also used to test the carbon dioxide content during the exchange of gas organisms. When the carbon dioxide content is higher than 0.04%, the initial red color turns yellow because the pH becomes more acidic. If the carbon dioxide content is lower than 0.04%, it changes from red to magenta and, in relatively low concentrations of carbon dioxide, becomes purple. Carbon dioxide, even in concentrations found in exhaled air, will dissolve in the indicator to form carbonic acid, a weak acid, which will lower the pH and give a distinctive color change. The color change to purple during photosynthesis shows a decrease in the percentage of carbon dioxide and is sometimes inferred as oxygen production, but there is actually no direct evidence for it.
Great care must be taken to avoid acid or alkali contamination of the equipment in the experiment, since the test is not directly specific to gases such as carbon dioxide.
Video Bicarbonate indicator
Composition
Two solutions are set up separately:
- Solution A: 0.02 g of blue timing, 0.01 g red cresol and 2 ml of ethanol
- Solution B: 0.8 g of sodium bicarbonate, 7.48 g of potassium chloride and 90 mL of water
- Dissolve Solution A and B and mix 9 ml of mixed solution to 1000 mL distilled water.
- This method to determine the concentration of bicarbonate and carbonate is also called "Magni method".
Maps Bicarbonate indicator
References
Source of the article : Wikipedia
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