Every wondered what makes bath bombs fizz? Follow this recipe to make your own DIY bath bombs at home (or at school) and find out the chemistry behind how they work.

You will need

  • food colouring
  • flower petals or body glitter
  • sweet almond oil
  • scented oil such as lavender oil
  • ten tablespoons of bicarbonate of soda
  • three tablespoons of citric acid
  • two large mixing bowls
  • one large muffin tray
  • one small glass jar
  • rubber gloves
  • spoon.

What to do

  1. Your homemade bath bombs will fizz when you put them into your bath water.

    Grease the sides and bases of a large muffin tray with a small amount of almond oil. Use an alternative oil if allergic to nuts.
  2. Place the citric acid and bicarbonate of soda into a large bowl. Mix the ingredients together well, to form the base mixture.
  3. Scoop out about half a cup of this mixture and put it in into another bowl. This will make about one or two bath bombs (depending on the size of the holes in your muffin tray). You could also use old plastic containers or anything that will hold a shape.
  4. Add the flower petals or body glitter to the base mixture.
  5. In the small glass jar, mix together 6 drops of your scented oil, 5 teaspoons of sweet almond oil and about 10 drops of food colouring.
  6. Gradually pour the oil mixture into the half cup of the base mixture. While wearing rubber gloves, quickly mix it all together. The mixture is ready when it stays together in your hands without crumbling too much.
  7. Spoon the mixture into the muffin tray. Press it down firmly.
  8. You can use the rest of the mixture with other types of scented oil or food colouring to make more bath bombs.
  9. Leave the bombs in the tray to set for a few days.
  10. Carefully up-end your bath bombs to remove them from the moulds.
  11. Run a bath, hop in and drop a bomb. Watch it fizzzzzz!

What's happening

When the bath bomb dissolves in water, there is a chemical reaction between the citric acid and the sodium bicarbonate. The result is called sodium citrate. During the reaction, carbon dioxide is released. This causes the 'fizzing' that you see, similar to that in carbonated water.

The sweet almond oil is released during this reaction. It will form a thin layer on your skin which can help to moisturise it. The lavender oil is for fragrance.

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