Fun Sparks – Acid or alkali? Making a red cabbage indicator.

Posted by ScienceSparks in Chemistry, Other | 4 comments

Acids and alkalis are substances that can be found in the science laboratory and at home all around us.

Acids can be found in the food we eat, in a bodies (like the stomach) and some acids can be very harmful.

Alkali’s are another group of chemicals that react with acids. Substances such as soap is an alkali and bicarbonate of soda which we use in baking but also harmful things like bleach and drain cleaner.

So how do we know when a substance is an acid or an alkali?

We use a substance called an indicator to test it. An indicator will change colour to determine an acid or alkali.

Where can I get indicator from?

Well today I will show you how to make one from red cabbage.

What you will need

A grater or blender
Red cabbage
Hot water
A saucepan
A sieve
Plastic cups
Different substances to test (I use bicarbonate of soda and vinegar and water but you could try any other substance in the home as long as supervised and act with caution) Wearing latex gloves and goggles are good safety practices when using chemicals.

Method

1. Grate or blend the cabbage. Both are actually time-consuming – I only used half a cabbage

2. Tip into a saucepan and pour over boiling water from the kettle.

3. Heat until simmering and leave for 10 minutes.

4. Sieve the water and cabbage into a jug – you will notice that the fluid is very purple in colour!

5. Leave to cool a bit – your indicator is ready

6. Place out plastic cups of the amount of substances you plan to test.

7. Add equal quantities of indicator to each cup

8. Dissolve some Bicarbonate of soda in water – measure out a set amount e.g 20ml Pour into the first cup. What happens?

9. Repeat this with the same quantity of each substance you test and record the colour change.

Results

In this case of red cabbage indicator the colour will change from purple to red if it is an acid and from purple to green if it is an alkali. The different shades of colour will depend on the strength of the acid or alkali. If there is no colour change the substance is said to be neutral.

Vinegar

Bicarbonate of soda!

 

 

 

So do you have something to show us this week for Fun Sparks? Craft, education or activities are all welcome!