Red cabbage

Public summary: 

We use a little red cabbage juice to find out more about acids and bases in the world around us.

Making a natural pH indicator.
Useful information
Kit List: 

Red cabbage
Knife/grater/rolling pin or other masher
Large Bowl for grated cabbage
Absorbent white paper

Packing Away: 

Wash down surfaces.
Cabbage waste can be binned.

Frequency of use: 

*** OVERVIEW ***

Cabbage juice is used as a pH indicator to demonstrate the concept of pH. Paper stained with cabbage juice will change colors when dipped in an acid (vinegar) or base (bicarb).

Possible Activities:
1) Dip the paper (with cabbage juice as indicator) into the acid and base to show the kids how it changes color.

Other things to talk about:
1) What are other examples of acids/bases?
2) What is pH?
3) Why does the juice change color in acids/bases?

Tips for demonstrating: If the kids want to, let them take home the pH paper!


Before Event:
1) Cut up half a head of red cabbage and grate it.
2) Crush it using a rolling pin. Strain the liquid into another beaker, and you should have a bluish/dark purple liquid – this is your basic universal indicator. When added to acids it should go pink, and in alkalis or bases it should go blue/green.

At Event:
3) If the cabbage still needs to be crushed/strained into a cup, ask the kids to help you.
4) Dip a piece of paper into the juice and explain that this juice will act as a pH indicator – in other words it will tell us whether something is acidic or basic.
5) Ask them if they know what pH is?
-tailor your explanation to the age of the child
-pH scale is a logarithmic scale defined by pH = -log10[H+] – for older kids
-pH is a number that tells you how acidic or basic something is [neutral substances, such as water, have a pH of seven, acids (vinegar/lemon juice) have a pH of less than seven, and bases (sodium bicarbonate) have a pH of more than seven.]
6) Ask them if they can name some acids/bases. (Lemon juice, bicarb, vinegar, orange juice, etc)
7) Explain that the cabbage juice will turn blue/green when dipped in a base and pink when dipped in an acid
8) Show them your two “mystery” liquids (vinegar and bicarb/water) – ask them to use the indicator paper to determine which one is an acid/base.

1) How can the cabbage juice act as an indicator?
-red cabbage contains coloured pigments called “anthocyanins” which have antioxidant properties
-in acidic conditions they lose an –OH group, and gain it in basic conditions
-most indicators gain an H+ in acidic conditions and lose in again in basic conditions
- This change in the physical structure will change the wavelength of light reflected off it, and so it changes colour
2) What would happen if we dipped the paper into water?
-Explain the concept of neutral substances.

Risk Assessment
Date risk assesment last checked: 
Wed, 17/01/2018
Risk assesment checked by: 
Date risk assesment double checked: 
Sun, 04/02/2018
Risk assesment double-checked by: 
Risk Assessment: 
DESCRIPTION Cut and grate red cabbage before the event. Then mash, eg. using a half rolling pin, to give pH indicator solution. Paint onto paper and observe colour change when lemon juice/vinegar or bicarb solution is added.
RISKS 1. Sharp knives and grater may cause cuts
2. Lemon juice/vinegar and bicarbonate of soda irritant to eyes
3. Children eating/drinking bicarbonate, lemon juice or vinegar.
ACTION TO BE TAKEN TO MINIMISE RISKS 1. Only demonstrators to use knives or graters to cut cabbage. Knives and graters to be kept concealed and out of reach for the duration of the experiment
2. Only use small amounts. Do not squirt.
3. Don't leave children with experiment unsupervised.
ACTION TO BE TAKEN IN THE EVENT OF AN ACCIDENT 1. Call first aider in case of injury
2. Wash with emergency eye wash provided if trained and confident to do so. Call first aider if necessary.
3. Advise parents that reactants are all edible, but to seek medical attention if child is feeling unwell as reactants may have been in box for unknown amount of time.
Publicity photo: