Activity sheet
Acids, Bases and Red Cabbage Indicator
What are acids and bases?
How to make red cabbage indicator
Acids and bases are two different types of chemicals.
When a substance contains acid it is described as acidic
and when a substance contains a base it is described
as basic.
Safety tip: this experiment requires the use of a knife
and hot water. Please ask an adult for assistance.
Most acids and bases found in our homes are quite safe,
but some strong acids and bases can be very corrosive –
they can even dissolve metal!
Lemon juice and vinegar contain weak acids, while
car batteries contain a very strong acid. Drain cleaner
contains a strong base, while hand soap contains a
weak base.
How do we tell them apart?
Acids tend to taste sour and bases usually feel slippery.
However, it’s not safe to touch or taste unknown
chemicals. Instead we can use special dyes called
indicators to tell them apart. Indicators change colour
when mixed with an acid or base, and safely tell us
whether a substance is acidic or basic.
Where do we get indicators from?
A lot of indicators are found in nature. Flowers, fruits
and vegetables, like geraniums, blueberries and red
cabbages contain indicators.
Red cabbage
Source: Museum Victoria
You will need:
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¼ of a red cabbage
Knife
Chopping board
Hot water
2 jugs
Strainer
Clear plastic cups
Teaspoon
Suggested test items
Geranium flowers
Source: Morguefile
Scienceworks
2 Booker Street Spotswood Victoria 3015
Melway: 56, B1
Phone: (03) 9392 4800
museumvictoria.com.au/scienceworks
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Water
Lemonade
Vinegar
Bicarbonate soda
Cream of tartar
Hand soap
Toothpaste
Shampoo
Lemon juice
Soap powder
Printed on recycled paper.
02/11
What to do:
1. Slice the cabbage, place it into a jug and carefully
pour the hot water over the cabbage.
2. Set aside the cabbage and water mixture for at least
10 minutes to allow the dye to seep into the water.
3. Once the water turns purple, use the strainer to
catch the cabbage and pour the coloured water into
the other jug. The coloured cabbage water is now
ready to use as an indicator.
To test if a substance is acidic or basic it needs to be
mixed with the indicator.
4. Using a fresh cup for each substance, fill the cup
about ¼ with the test liquid. If testing a powder
(for example cream of tartar), measure 1 teaspoon
into a cup and fill ¼ with water to dissolve.
5. Add some cabbage indicator to each cup and look for
colour change. Compare the colour change against
the chart below to find out if your test substance is
acidic, basic or neutral.
Red Cabbage Indicator Chart
Source: Museum Victoria
What’s happening?
Red cabbage contains a chemical called flavin that
changes colour when it is mixed with an acid or a base.
The colour change will depend on the strength of the
acid or base.
Acids turn the indicator different shades of red and
purple, while bases turn the indicator different shades of
blue and green. Liquids that do not change the colour of
the indicator are neutral - they are neither an acid nor a
base. Pure water is an example of a neutral substance.
Straining out the red cabbage
Source: Museum Victoria
Results of mixing red cabbage indicator with various substances
Source: Museum Victoria
Scienceworks
2 Booker Street Spotswood Victoria 3015
Melway: 56, B1
Phone: (03) 9392 4800
museumvictoria.com.au/scienceworks
Printed on recycled paper.
02/11