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Test the pH of whats around the house... with red cabbage!

pH is an important concept in chemistry. It is a measure of how acidic or alkaline a solution is. It describes the concentration of hydrogen ions in a solution (pH literally stands for "power of Hydrogen"). The pH of a substance is measured on a logarithmic scale (just like the coronavirus curve we are all trying to flatten!), and goes from 1 to 14. It inversely tells you the concentration of Hydrogen ions in the solution. Something with LOTS of hydrogen ions in solution will have a low pH (an acid), and a solution with FEW hydrogen ions in solution will have a high pH (an alkaline or basic solution). Water is neither acidic nor basic, it is neutral, so it has a pH of 7 - right in the middle of the pH scale.


Measuring the pH scale is fun because you can do it by colour, and classify things as basic or acidic based on what colour they turn when you add the special ingredient.... the indicator. Knowing the pH of something is important for lots of things. We test the soil and water around us to tell us important things about our environment, your doctor will use a pH test when she takes blood or urine samples, your food and everything you buy at the shops has probably had its pH measured to make sure it's safe to use and touch.


Red cabbage has a pigment (a coloured chemical) in it called anthocyanin, which changes colour when exposed to an acid or a base. You can test LOTS of things around the house and work out their pH, just using some boiled cabbage.


To make your own pH indicator using red cabbage you will need:

  • Some red cabbage

  • Boiling water

  • Different things to test (it works best if its a clear or fairly clear liquid, or anything that will dissolve in water). We used...

Lemon juice

Bicarb mixed into water

Washing detergent

Spray cleaning product

Bleach

Bore water

Rain water

Tonic water

(Then everything around the house the kids could think of to test)


Step 1: Cut up your cabbage and cover it with boiling water. The more you do, the more indicator you will get. We made about 1L of dark coloured indicator using a half a cabbage. A few big leaves would work if you didn't want much. Chop it up and soak it in boiling water for 10 minutes.





Step 2: Put the cabbage and water in the blender and whizz it up.


Step 3: Strain the cabbage water so that you have removed all the bits of cabbage, and have some dark purple coloured water. This is your indicator!





Step 4: Assemble the things you want to test. We tested 9 substances and lined them all up in clear glasses (we used wine glasses... everything else was in the dishwasher!). Fill the glass about halfway up with your test substances.





Step 5: Pour about 30mL of the cabbage water (we used egg cups so the kids could pour it in themsevles) into each glass and watch the colour change! Something that turns yellow or green has a HIGH pH and is an alkaline, or basic, solution. Something that turns pink or red has a LOW pH and is an acid. Blue is right in the middle, and is neutral.





You can line all your glasses up and work out what is the most basic, or the most acidic substance in the house!






NOTE: Don't drink any of the substances.


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