Ok this one is a good one. It’s quick, easy, slightly messy (but can be easily contained/managed) and kids love it. Also it is a super visual way to start to explain about chemical reactions and solids, liquids and gases. What’s not to love?!

What you need:

• Zip lock bags/freezer bags (essential – small ones will do)
• Bicarbonate of soda (essential – this has to be bicarb and not baking powder!)
• Lemon juice (essential – you can use vinegar instead but lemon juice smells a lot nicer!)
• Clothes pegs (essential – could use bulldog clips or something similar too)
• Warm water (not essential but can save on your lemon juice)
• Food colouring (not essential but adds some colour to the activity)

What to do:

• Pour some lemon juice into the bottom of a bag and add food colouring if using.
• Twist the middle of the bag a few times and then peg with a clothes peg or clip.
• Pour some bicarbonate of soda in the top and seal the bag up.
• Remove the peg, untwist and give the bag a little shake.
• Put on floor or in bath as quick as you can!
• Watch it explode!

Tips/extra bits:

• I have been a bit vague with amounts but it depends on the size of your bag as ti how much will explode it! Roughly 80ml or 1/3 cup of lemon and 2 tablespoons of bicarb will work for a small bag but experiment a bit to see what gives the best results.
• You can also add a bit of warm water in with the lemon juice as it will help to not use quite so much lemon. It needs to be warm to help with the reaction.
• Definitely do this somewhere you can contain the mess. Outside is good. Alternatively use the bath or kitchen sink. Plus this doubles up as a bit of clean as lemon and bicarb are both natural cleaning products! The sandwich bag can also be washed up and used again.

 

The Science Bit

What you have going on here is a chemical reaction. Carbon dioxide is being released as a product of this reaction, which is a gas and can be seen in the form of the bubbles. The molecules in the gas can move freely, this means they can change shape and volume. Solids (the bicarbonate of soda) remain the same shape and volume due to their molecules being held tightly together. Liquids (in this case the lemon juice) can change shape but not volume . This is because their molecules are close together but are being held less tightly than in solids. Think of them being linked but in a loose, ever changing way. In this experiment solid and liquid mix together and a gas is produced. Because the molecules in the gas are free to move the bag expands and eventually bursts.

Explaining it to children

Think about things that are either a solid, liquid and a gas and get the kids to think about their properties. Can you hold each one in your hands? What happens when you do? Can you change the shape of each one when you put it in a different container?

You could explain that everything is made up of molecules (tiny parts that we cannot see) and the molecules behave in different ways in a solid, liquid and a gas, which gives them their properties. Think of the molecules like people. In a solid everyone has to stand close together and keep in contact. To act like a liquid everyone holds hand; you can change the shape you make if people move around but you will always take up the same volume (total amount of space). For a gas everyone can just move around where they want, which is why when the gas is in the bag it can force it’s way out!

 

Experiment based on an activity from the fantastic The 101 coolest simple science experiments book.