This is a really magical experiment for kids of all ages. Pouring a purple liquid into a clear liquid and the color changes to a radiant pink, a bright yellow, a dark green or a deep blue- how fascinating, not just for kids.
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how to do it
Supplies you'll need
- red cabbage
- materials to test the pH, such as:
- baking soda
- vinegar
- lemon/lime juice
- sugar
- bleach (adult supervision necessary!)
- dish soap (hand soap is usually pH neutral)
- 6-7 glasses (depending on how many materials you want to test)
- chopping board, knife, pot, strainer
Get the red cabbage ready for your experiment
- Chop up the red cabbage into big chunks. (Let our kids help you with these safety gloves)
- Cover with water and boil for 10 minutes.
- Switch off heat and let stand for another 30 minutes.
- Strain cabbage but safe the water in a bowl.
The purple water is your pH indicator and you can pour it into your different test solutions (e.g. vinegar)
Prepare test solutions
- Pour water in 6 glasses (about half full)
- add to the first glass some lemon juice
- add vinegar to the second glass
- add baking soda to the third glass
- and so on…
- remember to leave one glass with just water for color comparison (that’s your control)
Do the experiment
I’m sure you kids already enjoyed all this prep work and are eager to finally see what’s going to happen when you mix the purple cabbage water with your test solutions.
Let your kids pour a little bit of the purple cabbage water into each of the solutions and watch how the color “magically” changes.
The science behind it
The purple pigment in the red cabbage is called anticyanins and is a pH indicator. That means that the pigment changes its color depending on the pH value.
The solutions we used in this experiment have different pH values. The vinegar and lemon juice are very acidic, meaning they have a very low pH value. Anticyanin changes to red or pink at an acidic pH (pH value below 7).
Sugar water, baking soda, dish soap and bleach have high pH values (pH value above 7), meaning they are basic. The purple cabbage dye changes to blue, green and yellow depending on how high the pH value is.
Water has a neutral pH value of 7 and acts as our control in this experiment. The cabbage water stays purple when added to only water.
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