Introduction
Sometimes, the things that show us if something is an acid or a base come from nature! Red cabbage is a great example, and so are very red roses.
The stuff in red cabbage that acts like an indicator is called an anthocyanin. Anthocyanins are water-soluble pigments that give red, blue, and purple colors to flowers, fruits, and vegetables. They’re even used as food coloring (E-163) and can be found in things like strawberries, plums, cherries, red cabbage, red onions, and eggplants. Anthocyanins are very sensitive to changes in how acidic or basic something is (we call this pH). Usually, they turn red in acidic stuff, blue in neutral stuff, and green in basic stuff.
Goal
To make a homemade indicator and use it to see which common household items are acidic and which are basic.
Materials
- Red cabbage
- Beakers (glass containers)
- Glass stirring rod
- Heat source (like a stove or a safe heating plate, ask an adult for help!)
- Stand and wire gauze (a metal screen to put on the stand)
- Filter paper
- Funnel
- Samples of: hydrochloric acid (ask a grown-up to handle this!), sodium hydroxide (ask a grown-up to handle this!), lemon juice, vinegar, ammonia (ask a grown-up to handle this!), bleach (ask a grown-up to handle this!), and baking soda.
How To Do It
- Take a leaf of red cabbage and chop a part of it into small pieces. Put the chopped cabbage into a beaker with about 50 milliliters of very hot distilled water (ask a grown-up to help you heat the water safely!). Stir it and wait for a little while until the water gets a good color.
- Pour the colored water through filter paper (using a funnel to help) into another container to get rid of any solid bits of cabbage.
- Add a few drops of the colored water you got (your indicator!) to each of your samples. Write down the color you see for each one.
