Chemistry Facts

08 Feb Chemistry Facts

A Chemistry tuition student at Miracle Learning Centre asked a teacher about this amazing phenomenon that she has seen on Instagram of a colour-changing drink at a local café:
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The drink was at first assumed by the student to be made up of alcoholic ingredients that are often seen to have these colour-changing properties. However, upon further research by the student about this colour-changing drink, the drink is actually non alcoholic – it is made up of purely tea!

Why can the tea change its colour from dark cobalt blue to purple?
Miss Ong, a teacher from Miracle Learning Centre replied, “The reason is actually very simple – it is due to the pH change in the drink! This tea is the butterfly pea tea – it is a natural pH indicator due to an anthocyanin, which is a water soluble pigment that acts as an indicator. Anthrocyanins are pink in acidic solutions (pH < 7), purple in neutral solutions (pH ~ 7), greenish-yellow in alkaline solutions (pH > 7), and colourless in very alkaline solutions. Therefore, based on the colour of the drink, it was most probably originally a slightly alkaline solution, and the acidity of the syrup, which most likely contains lemon juice, makes it more acidic. Acids donate hydrogen ions in an aqueous solution, and pH is the –log[H+], the increase in hydrogen ions means that pH is lowered and the pH level of the solution is decreased to indicate that it is now a neutral solution, and thus acting as an natural pH indicator.”

If you want to try out other homemade pH indicators, perhaps you could crush the juice of a red cabbage to get its colour. Red cabbage juice has, similar to the butterfly pea tea, anthrocyanins which works in the same way, sans the cost of the café price.

pH values are usually taught during Chemistry tuition lessons under the topic Acids, Bases and Salts. This article provides more insight than the usual syllabus that we cover. Do come back and read more of the chemistry tuition articles.

If you would like to find out more about pH levels, pH indicators and other applications of chemistry, do come on down to Miracle Learning Centre to find out more.

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