Colourful Chemistry

The chemistry of Polaroid photography – in C&EN

Preview image of the infographic - click through for the full image and alt-text
Click to view the full graphic on the C&EN site

Today (June 29) is National Camera Day, so it feels appropriate to share this recent graphic. Polaroid photography lets users snap a photo and print it on the spot. In the latest edition of Periodic Graphics in Chemical & Engineering News, we focus on the chemistry that makes this instant printing possible. Click through to the C&EN site to view the full graphic.

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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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The colour of alexandrite

The chemistry of colour-changing alexandrite

The colour of alexandrite
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Decades of marketing have placed diamonds on a pedestal above other gemstones. They’re an engagement ring tradition and are also found in lots of other jewellery. However, there’s another, coloured gemstone which is arguably superior. Not content with being one colour, it can display a whole range of hues, depending on the light falling on it. The gemstone in question? Alexandrite.
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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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