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Acids, Bases, and pH

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What is pH?

The “power” of hydrogen
A scale from 0 to 14 to specify acidity or basicity
Indicators are compounds that can be used to test pH
Examples of Indicators:

Methyl yellow
Phenol red
Bromothymol blue
Indigo carmine
Phenolphthalein
Litmus (lichen)
Universal Indicator
Anthocyanin

H₂O

Each indicator has a different colour chart

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Acids and Bases around the House

Many foods are acidic (stomach acid has a pH of ~1-2)
Many household cleaners are basic (pH > ~ 10-11)
Water is neutral

Colour chart is for Universal Indicator

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Red Cabbage Juice pH Indicator

Red cabbage contains anthocyanin, a type of pigment which is a natural indicator
acids will turn the cabbage juice red/pink
bases will turn the cabbage juice blue/green
Neutral substances will not change the colour: the cabbage juice will remain purple/blue

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Making Your Own Indicator

Get your parents to help! Use gloves (red cabbage stains!)

Don’t let your cabbage juice come into contact with anything acidic or basic while preparing it
Store juice in a clean jar
Juice will last ~1 week
Ask permission before testing any household chemicals

1. Slice 1 red cabbage into ~ 1” x 1” squares

2. Place cabbage pieces in pot of water. Boil, then simmer for ~10 minutes

3. Remove the cabbage leaves by pouring everything through a sieve

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What Else Contains Anthocyanin?

Acai berries
Blueberries
Chokeberries
Purple corn
Blood orange
Skin of eggplant
Grapes
Pansies

WHAT DO ALL OF THESE HAVE IN COMMON?

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Why did we choose Red Cabbage?

Red Cabbage is very concentrated in anthocyanin

data is from Wikipedia article about Anthocyanin. Red Cabbage data from: N. Ahmadiani, R.J. Robbins, T.M. Collins, M.M. Giusi: “Anthocyanins Contents, Profiles, and Color Characteristics of Red Cabbage Extracts from Different Cultivars and Maturity Stages”, J. Agric. Food Chem., 2014, 62(30), pp 7524-7531