Tag: acid

Infographic on litmus paper. The graphic explains how litmus dyes can be derived from orcinol, itself sourced from species of lichens. The chromophore of the litmus dye is 7-hydroxyphenoxazone. In acidic solutions, the protonated structure is red, while in alkaline solutions the deprotonated structure is blue.

What links litmus paper and lichens?

Infographic on litmus paper. The graphic explains how litmus dyes can be derived from orcinol, itself sourced from species of lichens. The chromophore of the litmus dye is 7-hydroxyphenoxazone. In acidic solutions, the protonated structure is red, while in alkaline solutions the deprotonated structure is blue.
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Along with universal indicator, litmus paper is one of the most commonly encountered pH indicators in school chemistry lessons. Unlike the range of colours produced by the former, litmus is pink-red in acidic solutions and blue in alkaline solutions. This graphic highlights its complex origins in lichens and the chemical changes that account for its colour change.

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Making a Red Cabbage pH Indicator

Making a Red Cabbage pH Indicator: The Method and the Chemistry

Infographic on making a pH indicator from red cabbage. The indicator can be made by roughly chopping cabbage, boiling, straining, and collecting the liquid. The extract contains anthocyanin pigments which give different colours in solutions of different pH, ranging from red, through purple, to green and yellow.
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We all know examples of everyday substances that can be classified as acids or alkalis: lemon juice is acidic, bleach is alkaline, and so on. Another substance that can be found in your kitchen can be used to test other substances to determine whether they are acidic or alkaline. The chemicals that give red cabbage its colour also allow it to be used as a pH indicator – this post looks at how!

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Colourful Chemistry - Colours of pH Indicators

The Colours & Chemistry of pH Indicators

Colourful Chemistry - Colours of pH Indicators
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Most of us, chemists or otherwise, have probably come across pH indicators at one point or another. I’d be surprised if there’s anyone out there who hasn’t, back in school, carried out the standard experiment of adding universal indicator to a variety of household liquids to identify them as acidic or alkaline. You might not be aware of the large range of different indicators that can be used to identify varying pHs, however, or the reasons behind the colour changes observed.

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