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 ?