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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]
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 .
Low pH colour Transition pH range High pH colour Thymol blue (first transition) Red 1.2 – 2.8 Yellow Methyl orange: Red 3.2 – 4.4 Yellow Methyl red: Red 4.8 – 6.0 Yellow Bromothymol blue: Yellow 6.0 – 7.6 Blue Thymol blue (second transition) Yellow 8.0 – 9.6 Blue Phenolphthalein: Colourless 8.3 – 10.0 Fuchsia
Plants contain pH-dependent pigments that can be used as pH indicators, such as those found in hibiscus, red cabbage (anthocyanin), and grapes . Citrus fruits have acidic juice primarily due to the presence of citric acid, while other carboxylic acids can be found in various living systems.
Red cabbage extract at low pH (left) to high pH (right) Anthocyanins generally are degraded at higher pH. However, some anthocyanins, such as petanin (petunidin 3-[6-O-(4-O-(E)-p-coumaroyl-O-α-l-rhamnopyranosyl)-β-d-glucopyranoside]-5-O-β-d-glucopyranoside), are resistant to degradation at pH 8 and may be used effectively as a food colorant ...
The main use of litmus is to test whether a solution is acidic or basic, as blue litmus paper turns red under acidic conditions, and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5–8.3 at 25 °C (77 °F). Neutral litmus paper is purple. [2]
Chopped cabbage and onions are sautéed in rendered bacon fat to create this simple dish, before being tossed with crisp pieces of bacon for texture. Different recipes may call for a variety of ...
Use of an inexpensive pH testing kit, where in a small sample of soil is mixed with indicator solution which changes colour according to the acidity. Use of litmus paper. A small sample of soil is mixed with distilled water, into which a strip of litmus paper is inserted. If the soil is acidic the paper turns red, if basic, blue.