Fun With Acids and Bases – How to Use Red Cabbage as an Indicator

Red cabbage acid base indicato original

Do kids want to learn about acids and bases? If they’re like my kids then probably yes in theory – but in practice, “Not right now, thanks Mummy, I’m just finishing this game on Grid Club/making this cardboard helmet/playing my guitar”.

Do kids want to play with colourful potions? Absolutely! And once you’ve ignited their curiosity, of course they’ll want to know all about it!

Bring on the red cabbage and those old faithfuls, vinegar and bicarbonate of soda…

What You Need

  • Red cabbage (we used half a head)
  • Water (the book says to used distilled water, but we used tap)
  • Saucepan
  • Stove Top / Hot Plate
  • Glass jars/glasses etc (to pour the cabbage water into)
  • Household substances to test eg vinegar, lemon juice, bicarbonate of soda, soap
  • Marker pen or dry wipe marker (optional) to label the jars
red cabbage acid base indicator homeschool science

What You Do

  1. Roughly chop the cabbage and boil it in water for about 10 minutes.
  2. Drain (and discard/eat) the cabbage, reserving the water.
  3. Pour the water into as many jars/glasses as you have substances to test, plus one as a control.
  4. Add one substance (e.g. lemon juice) to each jar of purple cabbage water. Label the jar so you don’t forget what you’ve added.
  5. Observe any colour change, comparing against the control cabbage water (to which nothing has been added).

What Happened

The water the cabbage has been boiled in is dark purple.

C and J both chose to add vinegar  to their first jar, which turned the cabbage water a pinkish colour. Then they predicted (proper science!) what would happen when they added lemon juice, and were happy to confirm their hypothesis that lemon juice also turned the water pink.

The effect of adding bicarbonate of soda was more subtle.  We had to scoop up a small amount of the liquid with a teaspoon to fully appreciate the change – the water took on a blueish hue.

Red Cabbage Acid/Base Homeschool Fun

Soap turned the water very slightly blue, and soy sauce had no noticeable effect.

What We Might Do Next Time

What we forgot to try (there’s always something!) is adding vinegar or lemon juice to our bicarbonate of soda water.  If you get the quantities right, this should turn the water back to the original (purple cabbage) water colour.

There are also lots of other substances we might test – orange juice, milk, Coca-Cola, tomato sauce…

How Does It Work?

Science Experiments Book

I’ll hand you over to the Science Experiments book here:

“An acid is a substance that produces positively charged particles made of oxygen and hydrogen, called hydronium ions, when dissolved in water…

A base is the chemical opposite of an acid.  Bases produce negatively charged particles in water, called hydroxyl ions….

Cabbage water [is an indicator, which means it shows] whether a liquid is acidic or basic. [It changes] colour because the structure of [its] molecules changes depending on the amount of hydronium or hydroxyl present.”

red cabbage acid base indicator homeschool science

Taking It One Step Further

For this you’ll need a pack of pH-testing litmus paper (£2.76 on Amazon).

red cabbage acid base homeschool science

I gave the children a book of litmus paper and they dipped a fresh piece in each of their cabbage water jars. They compared the colour the paper turned with the colour scale on the book, to obtain a pH value.

Red cabbage acid base indicator homeschool science

I explained that pH is a measure of the acidity or alkalinity of a solution. (Bases that dissolve in water are called alkalis.) Acids have low pH’s, alkalis have higher pH’s.

red cabbage and litmus acid base indicator - homeschool science

C noticed by testing with litmus paper that our soy sauce solution was very slightly acidic.

Has anyone else tried this? Do leave a comment to let me know how it went or if you know of any other fun experiements with acids and bases!

More Hands-On Science Posts

How to Make Slime and Plastic

Fizzy Fountains

Copper-Plating a Nail

Thanks to Adventures In Mommydom for hosting Science Sunday!

Science Sunday
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