Making our own pH indicators
• We often think of pH indicators as chemicals that can only be bought from chemical suppliers
• In fact, there are natural pH indicators all around us , if we know where to look
Same flowers.. different pH
Can you guess which flowers have been grown in alkaline soil and which have been grown in acidic soil?
Making Our Own Indicator copy
Juice from…
Colour at start
Colour with acid
Colour with alkali
Is this a good
indicator?
Red cabbage
Indicator from red cabbage
• Take some chopped red cabbage and put it into a mortar and pestle
• Add 10ml of water (use a measuring cylinder)
• Grind up the cabbage
Cabbage
10ml of water
Mortar and pestle
Filter the cabbage juice
• Divide the filtered juice evenly between 2 small beakers
• Add a small drop of acid to one …
• And a small drop of alkali to the other
• Note the results in your table
acid
alkali
Indicator from flowers
• Take some flower petals and put them into a mortar and pestle
• Add a small amount of alcohol
• Grind flower petals • Pour the juice
through a strainer
Petals
ethanol
Mortar and pestle
ethanol
Tea strainer
• Divide the strained juice evenly between 2 small beakers
• Add a small drop of acid to one …
• And a small drop of alkali to the other
• Note the results in your table
acid
alkali
• If there is time , repeat the process with different petals or vegetables
• Which juice do you think makes the best indicator?
• Why do you think this ?
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