Science talk With Chris Duggan House of Science

Chris Duggan is a scientist, educator, mother of two adult daughters, and farmers wife. After many years teaching secondary school Science and Chemistry, she switched her focus to primary schools by setting up a charity called House of Science in 2013. This large organisation supports thousands of teachers with science resource kits and professional development.

See what Chris has to say in her latest blog below.

Have you ever tried a bath bomb before? They're these amazing, scented spheres that can make for a colourful and aromatic addition to your bathtime.

Children think that they are wild and fun for their bathtubs and adults use them as a relaxing and luxurious way to pamper themselves after a long day.

To us, at House of Science, the most fascinating aspect of a bath bomb is the science behind them.

Have a go at creating your own fizzy bath bombs in the image of your favourite planet.

Photo: Supplied.

We promise they'll smell better than the planet Uranus which has hydrogen sulfide gas found in its cloud tops.

NB: Make sure that you use your bath bombs relatively quickly, as the citric acid and bicarbonate will oxidize over time, causing them to be less reactive in the water. The suggested shelf life is around six months.

Equipment:

• Baking soda aka bicarbonate of soda or sodium bicarbonate
• Citric acid
• Food colouring (as many different colours as you would like)
• An essential oil suited to bath use e.g., lavender, peppermint
• Bowls
• Spoon
• Sphere bath bomb mould (optional, available from craft stores), OR plastic wrap

Photo: Supplied.

Instructions:

1. Choose your favourite planet to turn into a bath bomb.

2. In a bowl, mix equal parts baking soda and citric acid. To get the correct amount for your mould, heap one half of the mould with baking soda, and the other half with citric acid then pour them both into the bowl. If you do not have a mould use about a quarter of a cup of each.

3. Add a couple of drops of essential oils and mix the oils evenly.

4. Split the mixture into as many bowls as you'd like colours

5. Add a different food colouring to each bowl. Use the least amount of food colouring possible to achieve the colour you want. Keep it to 2-4 drops, mixing it in drop by drop. Too much liquid will make your bath bomb sticky and hard to work with.

6. Fill the bath bomb mould trying to match the colours to the planet. Pack each half tight, then press them together to dry. No mould? Use your hands to squeeze the mixture into a ball shape and wrap in plastic wrap.

7. Leave the bath bomb to dry and set for 4 hours.

8. Carefully remove the bath bomb from the mould or plastic wrap. Now it's ready to use in the bath!

The Science Behind the Fun: The 'bomb” aspect of a bath bomb is the fizziness. But what's going on in those bath bombs that make them so fizzy? Two of the main ingredients are baking soda and citric acid. These two ingredients are what cause the delightful fizz when the bath bomb enters the water.

When sodium bicarbonate (baking soda) dissolves in water, sodium ions separates from the carbonate ions. The citric acid is also dissolving, resulting in hydrogen ions separating from the rest of the molecule. When the released hydrogen ions from the citric acid encounter the carbonate ions from the baking soda another reaction happens. This time, carbon dioxide gas is released as one of the end products. The carbon dioxide forms bubbles in the bath water and rush to the surface with an amazing fizz.

Research idea:

How many different elements can you name? Can you guess which of those elements might be present in this experiment? Research the chemical formula of Sodium bicarbonate and Citric Acid. What other compounds or substances have the same type of elements?