Did you know there’s a science lab in your kitchen?

Kitchen Chaos is your opportunity to get hands on and try some real science at home.

You’ll be able to have a go at extracting DNA from onions and make your own margarine. You’ll even be able to make your own pH indicator to test acids and alkalis around you’ll find under your kitchen sink.

We’ll also explain some of the science we see every day - from heat transfer to rising bread, you’ll be able to understand more about the science of everyday life.

Acids and alkalis

Acids and Alkalis (also known as ‘bases’) have the ability to change the colour of certain vegetable materials. One common vegetable whose colour is able to respond to acids and alkalis is the humble red cabbage. In fact, it makes a very effective pH indicator. Why don’t you have a go at testing some common chemicals around your home with your own red cabbage pH indicator?

Red cabbage as a pH indicator

Red cabbage contains a pigment called flavin, which is an anthocyanin. Anthocyanin is the red/purple pigment that is found in autumn leaves, red poppies, grapes, pea flowers and blackberries. Very acidic solutions will turn this pigment a red colour. Neutral solutions result in a purple colour and basic solutions appear greenish yellow. Indicators, such as the one we’re about to make, acquire a proton at low pH but lose it at higher pH. The structure of the anthocyanins changes on protonation such that the molecule absorbs light of a different frequency and thus reflects light of different frequency.

PH is a measure of how ‘acidic’ a solution is, so the lower the pH, the more acidic the solution. An acidic solution has an excess of protons (or H+), and a pH indicator is able to acquire these protons to affect the colour change.

In chemical terms, pH means “the negative log of the concentration of protons” in solution, which is written pH = -log[H+].

So, for example, if the concentration of H+ is .01M, the pH will be:

-log[.01] = -log[10 -2] = -(-2) = 2 (very acidic!)

Make your own red cabbage pH indicator

When juice is extracted from a red cabbage, it’s a very dark red/purplish colour.

You will need:

• red cabbage
• blender
• hot or boiling water
• strainer or filter paper

Test solutions

To test your pH indicator, try some of these:

• antacids (calcium carbonate, calcium hydroxide, magnesium hydroxide)
• baking soda (sodium bicarbonate NaHCO₃)
• cream of tartar (potassium bitartrate KHC₄H₄0₆)
• household ammonia (NH₃)
• lemon juice (citric acid, C₆H₈0₇)
• soda water (carbonic acid, H₂CO₃)
• vinegar (acetic acid, CH₃C00H)

Method:

Chop the cabbage into small pieces. Place about 2 cups of cabbage in a blender, cover with boiling water and blend. Strain or filter out the cabbage to get the red/purplish liquid.

Alternatively, if you don’t have a blender, place the cabbage in a glass container and add enough boiling water to cover. Let it sit for about 10 minutes to allow the colour to leach out of the cabbage. Strain or filter to extract the liquid.

This liquid is about pH 7 (neutral) but its exact colour will depend on the pH of the water.

Pour some of the liquid into a number of different containers (beakers are ideal, but cups would be fine) Add to each container some of the test solutions and note the change in colour.

Litmus paper

You can make your own litmus paper by taking either blotting paper or filter paper and soak it in a concentrated red cabbage juice solution.

After a few hours, remove from the solution and allow to dry. Cut into strips, and voilà - home made litmus paper!

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