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Extracting anthocyanins from household plants, especially red cabbage, to form a crude pH indicator is a popular introductory chemistry demonstration. Litmus, used by alchemists in the Middle Ages and still readily available, is a naturally occurring pH indicator made from a mixture of lichen species, particularly Roccella tinctoria.
A gradient of red cabbage extract pH indicator from acidic solution on the left to basic on the right. Red cabbage contains an anthocyanin-based dye that can be used as a pH indicator. It is red, pink, or magenta in acids (pH < 7), purple in neutral solutions (pH ≈7), and ranges from blue to green to yellow in alkaline solutions (pH > 7). [7]
Anthocyanins may be used as pH indicators because their color changes with pH; they are red or pink in acidic solutions (pH < 7), purple in neutral solutions (pH ≈ 7), greenish-yellow in alkaline solutions (pH > 7), and colorless in very alkaline solutions, where the pigment is completely reduced.
The buffering capacity of the water probably overwhelmed the small amount of acid in the cabbage drippings, bringing the pH back to ~7 and turning the color blue. It's not that the tap water was very basic, it's just that it was less acidic than the juice. -- 174.21.247.23 ( talk ) 04:10, 17 February 2010 (UTC) [ reply ]
A roll of universal indicator paper Colors of universal indicator. A universal indicator is a pH indicator made of a solution of several compounds that exhibit various smooth colour changes over a wide range pH values to indicate the acidity or alkalinity of solutions. A universal indicator can be in paper form or present in a form of a ...
It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity. In an acidic medium, blue litmus paper turns red, while in a basic or alkaline medium, red litmus paper turns blue. In short, it is a dye and indicator which is used to place substances on a pH scale.
This category contains articles about pH indicators: chemical compounds which change colour or fluorescence in response to changes in pH Wikimedia Commons has media related to PH indicators . Subcategories
The indicator is used in photosynthesis and respiration experiments to find out whether carbon dioxide is being liberated. [1] 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.