Blog

There’s something soothing about a cup of lemon tea. But there’s some fun chemistry happening in that cup too!

Safety: This activity uses a hot kettle, and you may need to juice lemons. Ask an adult to help. Use clean hands and clean equipment.

You will need

• Kettle
• 2 teacups
• 2 black tea bags
• Lemon juice
• Bicarb soda
• Teaspoon
• Honey

What to do

1. Put about 500 mL of water in the kettle and boil it.
2. While the water is boiling, put a tea bag into each teacup.
3. When the kettle is done, carefully pour half of the hot water into each teacup.
4. Start a timer for five minutes.
5. When the timer is finished, take the tea bags out of each cup.
6. Look at the two teacups. Are the teas the same colour?
7. Add about a tablespoon of lemon juice into one cup.
8. Add a tiny bit of bicarb soda to the other cup – no more than a quarter of a teaspoon.
9. Look at the two teacups. Are the teas the same colour now?
10. Add a couple of teaspoons of honey to the lemon tea and enjoy.
11. The bicarb tea will taste bad, so pour that one down the sink!

What’s happening?

Tea might seem simple, but this experiment shows there’s a lot of chemistry hiding in this drink!

Tea is a pH indicator, which means it changes colour based on how acidic it is. Adding lemon juice makes tea more acidic and look paler. Adding bicarb soda will do the opposite, making tea more alkaline and darker in colour.

Theaflavins and thearubigins are the main chemicals that give black tea its distinctive colour. These groups of chemicals are known as tannins, and they’re part of a larger chemical family known as polyphenols, which are pH sensitive.

Tannins also have a bitter taste and are astringent, which means they make your mouth pucker up and feel dry. You might notice the bitterness and astringency in tea, particularly if you drink it black with no sugar.

So what other chemicals are in a cup of tea? There are thousands! Of these, caffeine is probably the most famous (apart from water!). Caffeine is a stimulant, which means it can block feelings of tiredness or sleepiness. A cup of tea in the morning can help you wake up, but too much tea can make it hard to go to sleep, so be careful!

If you’re after more science activities for kids, subscribe to Double Helix magazine!