Red Cabbage Indicator (Science Box Experiment 4)

As part of CoCoMAD, Royal Society of Chemistry have funded science boxes which are being distributed to local school children - however - the experiments are available online for anyone to take part!

Below you’ll find the experiment introductions, equipment list, method, questions to explore and - very important - health and safety information.

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Introduction

There are many chemicals that change colour when mixed with acids or alkalis and these are known as indicators.

Naturally-occurring indicators include those found in grape juice, turmeric and hydrangea flowers. Red cabbage also contains a chemical called anthocyanin which is an indicator for acids and alkalis:

Equipment List

· A white dish (to give good colour contrast) or a small glass

· Pipette (dropper or syringe will be fine)

· Sieve

· Plastic screw top container

· Blender or pestle and mortar

· Red cabbage (NOT included in the box)

· Bicarbonate of soda(or toothpaste)

· Citric acid (or vinegar)

· Water

What to do

IT IS IMPORTANT THAT YOU HAVE READ THE HEALTH AND SAFETY SECTION BEFORE CARRYING OUT THE ACTIVITY – THE ROYAL SOCIETY OF CHEMISTRY, FRIENDS OF COTTERIDGE PARK AND THE DEVELOPER DO NOT ACCEPT ANY LIABILITY

Method 1

Place some red cabbage in a blender with some water and blend (a pestle and mortar can be used as an alternative).
Add more water to loosen the mixture if needed.
Sieve the blended mixture the liquid (which is the filtrate)
The liquid is your indicator, it can be kept in a sealed container until you need it

Method 2:

If you are already boiling some red cabbage for dinner then keep the liquid after cooking and allow it to cool.
The liquid is your indicator, it can be kept in a sealed container until you need it.

Using the indicator

Make up an alkali solution by dissolving a little bicarbonate of soda in 50 ml water.
Make up an acidic solution by dissolving a little citric acid in 50 ml water
Using a pipette make a small puddle of red cabbage indicator in a dish (or put some in a glass) and note what the colour is.
Using a clean pipette add alkali solution dropwise (one drop at a time) to the puddle of red cabbage indicator see if the colour changes.
In another dish make another small puddle of red cabbage indicator (or put some in a glass).
Add acidic solution dropwise to the indicator and note the colour change
IMPORTANT: Always rinse pipettes and weighing boats between each use – this is good scientific practice and avoids contamination.

Things to investigate

Add drops of other common household products (e.g. toothpaste mixed with water) and foods (such as lemon juice) to fresh red cabbage indicator to see which are acidic or alkaline (DO NOT use corrosive acids or alkalis such as bleach).

Health and Safety
(remember to always use common sense)

Risk(s) & Precaution(s)

Risk of hand injury (from blender or pestle and mortar)
Seek help from an adult to prepare the red cabbage indicator

Where can I learn more?

Red cabbage indicator (RSC website): https://edu.rsc.org/resources/outreach-red-cabbage-ph-indicator/1214.article
Acids and bases (RSC resource): https://edu.rsc.org/resources/acids-and-bases/564.article

Feedback

We really hope you enjoy the experiments and would love your feedback on the activities and on the science activities and talks at Virtual CoCoMAD (4th July).

To send feedback please use the QR code or the link below to get to the feedback form which will probably take about five minutes to complete. If you do you will be invited to leave your email address and you will be entered into a draw to win a pack of RSC Periodic Table Top Trumps.