Tools and Materials

To prepare your Christmas tree:

  • 45 white pipe-cleaners
  • Scissors
  • 2 cups of water
  • A kettle
  • 2 containers that can each hold at least 250 ml of hot liquid
  • Bicarbonate of soda (also called bicarb soda and sodium bicarbonate)
  • 3 spoons
  • A slotted spoon
  • Some paper towel
  • 2 baking trays or plates
  • 75 g of citric acid (you can find this in the supermarket)
  • 15 small, white pompoms

To make your Christmas tree:

  • A toothpick or skewer
  • A small foam cone (about 10 cm tall)

To make your pH indicator:

  • 500 ml of hot water (from the tap)
  • 3 large red cabbage leaves
  • A blender or mixer
  • A kitchen strainer
  • A mister or spray bottle

To reveal your Christmas colour:

  • A baking tray or plate
  • Some sheets of newspaper

What to do

Warning

Adult supervision is needed. Hot water, an electric blender/mixer, scissors and a skewer can all be dangerous. Ask an adult to help with this activity.

Preparing your Christmas tree:

Do this the day before you want your Christmas tree!
  1. Gather your materials on a flat surface, like a desk or kitchen table.
  2. Use the scissors to cut the pipe-cleaners into 2.5 cm lengths (these don’t need to be exact).
  3. Boil the water in the kettle.
  4. Pour 1 cup of the boiled water into a container. Use a spoon to add bicarbonate of soda to the hot water, one spoon at a time, while stirring with another spoon. Stop adding bicarbonate of soda when no more will dissolve in the water.
  5. Add the pipe-cleaner pieces to the bicarbonate of soda solution and stir with the spoon for 30 seconds. Using the slotted spoon, carefully remove the pipe-cleaner pieces and place them on some paper towel. Rinse the slotted spoon.
  6. Pat dry the pipe-cleaners with some paper towel. Lay the pipe-cleaners in a single layer on a baking tray or plate and leave them to dry.
  7. Pour half a cup of the boiled water into the other container. Slowly add the citric acid to the hot water, stirring with a clean spoon to ensure that it all dissolves.
  8. Add the pompoms to the citric acid solution and stir with the spoon for 30 seconds. Using the slotted spoon, carefully remove the pompoms and place them on some paper towel.
  9. Pat dry the pompoms with some paper towel. Lay the pompoms in a single layer on a baking tray or plate and leave them to dry.
  10. Leave the pipe-cleaners and pompoms to dry overnight. Once they are dry, you’re ready to make your Christmas tree!

Making your pH indicator:

  1. Add the hot water and red cabbage leaves to the blender or mixer.
  2. Place the lid on the blender and blend until smooth.
  3. Pour the mixture through a strainer to take out any solid pieces of cabbage. Make sure you put something underneath the strainer to catch the liquid!
  4. Carefully pour the red cabbage indicator liquid into the mister/spray bottle. You can store it in the refrigerator for up to 5 days.

Making your Christmas tree:

  1. Gather your materials on a flat surface, like a desk or kitchen table.
  2. Use the toothpick or skewer to poke holes around the small foam cone. Don’t poke holes on the flat end (the base) of the cone – this is what your Christmas tree will be sitting on.
  3. Insert pipe-cleaner pieces into the holes to create the branches of the tree. Once you have poked enough pipe-cleaner pieces in to fill the rounded part of the cone, you may want to bend and shape them gently to make it look more like a tree.
  4. To finish decorating the tree, gently wedge some pompoms between the pipe-cleaner branches.

Revealing your Christmas colour:

  1. Before spraying the tree, you should be aware that the red cabbage indicator can stain. Perform this part of the activity where it’s okay to make a mess, like a laundry or the backyard.
  2. Gather your materials on a flat surface. If you’re doing this activity inside, line the table with newspaper or a sheet of plastic to collect any drips.
  3. Place the tree on a wide plate or tray.
  4. Spray the red cabbage indicator evenly onto your Christmas tree. The more you spray, the more colour you will reveal! Try letting the tree dry a little before spraying it again.

Questions to ask

Did your tree change colour? If not, try spraying on more red cabbage indicator.

What colour did the pipe-cleaners change to when you added the indicator? What about the pompoms?

Why did the pipe-cleaners and pompoms turn different colours? Think about the bicarbonate of soda solution and the citric acid solution that you soaked them in – what is different about them?

What's happening

The pH tells you how acidic or basic (also called alkaline) a solution is. If there are more hydrogen ions (H+) than hydroxide ions (OH-), the solution is acidic (pH between 1.0 and 6.9). Citric acid solution is a type of acid. If there are more hydroxide ions than hydrogen ions, the solution is alkaline (pH between 7.1 and 14). An example of an alkaline solution is bicarbonate of soda solution. If the amounts of the 2 ions are the same – like in pure water – the solution is neutral (pH of 7.0).

A pH indicator is a chemical that changes colour depending on how acidic a solution is. These chemicals can be used to measure the pH of the solution. Red cabbage is a natural pH indicator. At a pH of 7.0 (neutral), the red cabbage indicator is a purple-blue colour. At a low pH (acid), the red cabbage indicator turns red. At a high pH (base), the red cabbage indicator turns green. This is why the indicator turns different colours when it touches different parts of the Christmas tree.

Did you know

Lots of coloured plants contain pigments that react to acids and bases. The pigment we extracted from cabbage, called anthocyanin, is also found in berries, tree leaves and flowers. Flowers like hydrangeas are very sensitive to changes in pH and will actually grow different colours depending on the pH of the soil. Some gardeners use this to control the colours of the flowers.

Turmeric, which is a spice used in cooking, is another type of natural indicator. Unlike the red cabbage indicator, turmeric only has one colour change: from yellow to red in alkaline solutions (pH greater than 8.6).