Yummy Science – Secret Messages. Experiments you can try in the kitchen – Custard Bouncing Balls, Magical Water, Growing Crystals, Spud Guns, Designer Onions, Honeycomb Toffee, Sticky Milk, Toast Busters, Toasty Science, Self Slicing Banana

How it's done

We tried this experiment with Northsound1, listen to the results:

Photos

Science Links

Other links:

More fun nutrition activities at
the Rowett Research Institute, eduweb
Check out National Science & Engineering Week at:
The BA (British Association for the Advancement of Science)

Further food science ideas for the primary aged audience are presented in the ‘Food for Thought resource, downloadable at The BA

For secondary pupils, there are lots of great kitchen chemistry ideas available in the Salters Chemistry Club handbooks or in various publications produced by the Royal Society of Chemistry

Exploring the science:

Method 1: The lemon juice is oxidised (burnt) in the oven to produce a brown colour. The oven temperature isn’t high enough to burn the paper so that you end up with brown writing on a white paper background.
Method 2: Red cabbage water is an indicator - a chemical which turns different colours according to the acidity or alkalinity of the solution it is added to. In neutral solutions it is a purple colour but it turns pink with acid (the lemon juice) leaving a pink message on a pale purple coloured background.
Method 3: Red cabbage water is an indicator it turns green with an alkali (the bicarbonate of soda) leaving a green message on the paper.
Method 4: Iodine solution is used to test for starch. The iodine reacts with the starch in the paper to give a message in dark blue writing. When the lemon juice is painted over the top of the writing, the Vitamin C (ascorbic acid) in the juice reacts with the iodine to make a new colourless compound and the writing disappears.

Taking it further:

Try soaking some blotting paper in red cabbage water and then allowing to dry. Use your paintbrush to draw a picture, dipping the paint brush into acidic solutions e.g. lemon juice, vinegar, fizzy drink and alkaline solutions e.g. bicarbonate of soda, washing up liquid. According to the acidity or alkalinity of the solutions, the treated blotting paper will turn different colours producing an amazing multicoloured picture!
The pigment molecule in the red cabbage water involved in the colour changes is called flavin which is an anthocyanin. Anthocyanins can be extracted from other plants, including the flowers of geranium, poppy and rose; the berries of and blueberry; the stems of rhubarb. Try making yourself another indicator solution using one of these plants.

Safety:

Adult supervision required when using oven danger of burns.

Ever fancied yourself as a spy? Well you will need a bit of knowledge about secret messages, how to write them and how to read them. Follow the instructions below and have some fun….

You’ll need:

Lemon juice
Red cabbage water*
Bicarbonate of soda (from home baking section of supermarkets)
Iodine solution (available as ‘iodine tincture’ from chemist shops it is used as an antiseptic for treating minor wounds)
Paintbrushes (or cotton buds)
Lump of cotton wool
Paper

*To make red cabbage water, chop some red cabbage, cover with water, bring to boil and simmer for approximately 5 minutes, strain off cabbage (of course the cabbage makes a delicious vegetable to eat with your evening meal!), retain liquid (which will be a reddish/purple colour) and allow to cool.

What to do:

Method 1: Using a paintbrush, write a message on a piece of paper using lemon juice. Allow to dry (message becomes invisible). To reveal the message, put the paper on a shelf in the oven at 175°C and check every few minutes until message appears. (Milk, apple juice and onion juice can be substituted for the lemon juice and will behave in just the same way).

Method 2: Using a paintbrush, write a message on a piece of paper using lemon juice. Allow to dry (message becomes invisible). Then use a lump of cotton wool to wipe red cabbage water all over the paper.

Method 3: Dissolve a teaspoon of bicarbonate of soda in a small amount of warm water. With a paintbrush, write a message on a piece of paper and allow to dry (message becomes invisible). Then use a lump of cotton wool to liberally wipe red cabbage water all over the paper.

Method 4: Add 3-4 drops of iodine solution to a tablespoon of fresh water. Use to write a message with a paintbrush on a piece of paper. Then take a lump of cotton wool dipped into lemon juice and wipe over the written message.

What happens:

Method 1: The writing turns brown.
Method 2: The writing turns red.
Method 3: The writing turns green.
Method 4: The writing turns dark blue but then disappears when the lemon juice is painted over it!