Red cabbage magic potion

Purple red-cabbage juice changes colour like magic: pink with vinegar, blue-green with bicarbonate. A real wizard's potion.

Age : age 4+; the grown-up makes the juice

Materials

• A quarter of a red cabbage
• A pan of water and a sieve : For the grown-up.
• Clear glasses : At least 4.
• White vinegar and lemon juice : The "acid potions".
• Bicarbonate of soda : The "powder that turns things blue".
• A spoon per ingredient

Steps

Make the magic juice

1. The grown-up cuts the cabbage into strips and simmers it for 10 minutes in the water.
2. Strain and let it cool: the juice is purple.
3. Pour the same amount of juice into each glass.

Do the magic

1. Glass 1: leave it alone, it's the control glass.
2. Glass 2: add a spoonful of vinegar. It turns pink!
3. Glass 3: add lemon juice. Pink too?
4. Glass 4: add a spoonful of bicarbonate. It turns blue or green.
5. Last trick: pour vinegar into the blue glass. It fizzes and turns purple, then pink again.
6. Write down the colours on a sheet: it's a real scientist's chart.

Red cabbage juice contains a pigment that changes colour depending on whether a liquid is acidic or not. Vinegar and lemon are acidic: the juice turns pink. Bicarbonate is the opposite of an acid (a base): the juice turns blue or green. Chemists call this an indicator.

Test other kitchen liquids: fizzy water, milk, soapy water. Guess the colour before pouring!

If it goes wrong

• Juice too pale : Less water, or boil the juice down.
• No clear change : Add another spoonful.
• Strong smell : Open a window; it soon goes.

Safety

• Only use kitchen products: never household products (bleach, laundry detergent) to test colours.
• The hot pan is for the grown-up; potions are not for drinking.

Sources

• Wikidébrouillard, liquide qui change de couleur
• Les parents créatifs, chou rouge qui change de couleur

All activities