An indicator is a chemical compound that is added in small amounts (usually to a solution) so that the pH (acidity or alkalinity) of the solution being tested can be visually determined.
Indicators used in science:
The are several common laboratory pH indicators. Indicators usually exhibit intermediate colours at pH values inside a transition range. For example, phenol red exhibits an orange colour between pH 6.8 and pH 8.4. For more information http://en.wikipedia.org/wiki/PH_indicator
Naturally occurring indicators:
Many plants or plant parts contain chemicals from the naturally-coloured anthocyanin family of compounds. They are red in acidic solutions and blue in basic. Anthocyanins can be extracted with water or other solvents from a multitude of coloured plant parts, including from leaves (red cabbage); flowers (geranium, rose petals, poppy); fruit or berries (blueberries, blackcurrant, cranberries, grapes); stems (rhubarb); and roots (beetroot). Extracting anthocyanins from household plants, especially red cabbage, to form a crude pH indicator is quite straightforward.
Anthocyanins are water-soluble pigments that may appear red, purple, or blue according to the pH of the solution they are in. In flowers, bright reds and purples are adaptive for attracting pollinators. In fruits, the colourful skins also attract the attention of animals, which may eat these and disperse seeds. In photosynthetic tissues (such as leaves and sometimes stems), anthocyanins have been shown to act as a “sunscreen”, protecting cells from light damage.
cabbage / beetroot
Chop or grate cabbage / beetroot and boil in small amount of water until the colour is released into water (about 15 mins or so). Strain off solids and use liquid once cooled.
pH colour changes for cabbage/beetroot
Red – pH around 2 (acidic)
Purple – pH around 4 (acidic)
Violet – pH around 6 (acidic)
Blue – pH around 8 (basic)
Blue/green – pH around 10 (basic)
Green – pH around 12 (basic)
Make very strong tea and allow to cool.
grape juice / cranberry
Either juice your own fruit or use store bought juice. Strain to remove debris.
Blend blueberries/blackberries and strain to remove debris. If the colour is too dark to see a colour change, can add water to lighten (ensure water is pH neutral).
There are several different recipes for this –
4 tsp turmeric in 1/4 cup water or
4 tsp turmeric in 1/4 isopropyl alcohol (rubbing alcohol) (not edible) or
4 tsp turmeric in 1/4 cup methylated spirits (not edible) or
Personally I haven’t experimented with vodka or other edible alcohols, but they may work.
Turmeric indicator paper
- Add 2 tsp turmeric and 75mL methylated spirits to a cup and stir well.
- Place thin tissue or toilet paper flat onto a dinner plate.
- Allow turmeric to settle to bottom of cup, then pour yellow liquid onto paper.
- Once paper is dry, cut unto strips or shapes.
- Use as indicator paper (keep dry when not using).
pH colour changes for turmeric
Yellow – pH 1 to 7 (acidic or neutral)
Red – pH above 7 to pH 12 (basic)
ACIDIC AND BASIC FOODS
Acidic – citrus fruits and juice, ascorbic acid, vinegar, apple cider, yeast
Basic – bicarbonate soda
for a comprehensive list of food pHs see http://www.fapc.okstate.edu/files/factsheets/fapc118.pdf
IDEAS FOR USING pH IN FOODS
- Add splash of orange juice (or something laced with ascorbic acid) to blueberry juice and watch the colour change. (ie guests add the two drinks together).
- Beetroot and blueberry juice cocktail – add apple cider.
- Layered “drink” – different pHs for different coloured layers.
- Add dry ice to make carbonic acid (as the carbon dioxide dissolves into the liquid) and the solution acidic – changes colour as it bubbles
- Make some sodium alginate / calcium lactate bubbles of acidic or basic solution – puncture once added to a pool of beetroot juice. Watch colour change.