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.
Following on from the start of the Chemistry Advent Calendar yesterday, here’s another festive post, this time looking at the chemistry of the poinsettia plant. The red leaves of the poinsettia plant can be used to make a pH indicator, due to their chemical composition; this is actually something of an upgrade on one of the oldest posts on the site, now complete with a explanatory graphic!
I’m making pH indicator paper with some of my classes this week, using the coloured leaves of red poinsettia plants, which set me thinking about the chemistry behind why these plants can be used as indicators.
Poinsettias have a reputation for being poisonous – a claim that is in fact entirely unfounded. A quick google search will reveal that the myth of poisonous poinsettias potentially originates from a ingestion of poinsettia leaves being mistakenly attributed as the cause of poisoning of an american child in 1919. Not being poisonous obviously isn’t quite the same as being edible, and eating poinsettia leaves can potentially cause stomach pain and vomiting – but there have been no recorded deaths as a result of the plant. As its leaves also have a reportedly ‘indescribably awful’ taste, few could probably bear more than a nibble.
