We’ve made normal lava lamps and spooky lava lamps and now pumpkin lava lamps. These are so easy and very impressive to watch.
You could try different colours or add glitter, how about making one to look like a witch or ghost?
You will need
- A clear plastic bottle or jar
- A bottle of vegetable oil
- Orange food colouring
- Alka Seltzer
- Black pen and pipe cleaners for decoration
Fill the bottle or jar a quarter full with water, add some orange food colouring and mix well.
Top up to the (near) top with the vegetable oil.
They should separate into two layers, water at the bottom and oil sitting on top.
Decorate as you wish, we used these brilliant pens kindly sent to us from Craft Merrily to draw the face.
Pop in half an alka seltzer tablet and watch what happens.
Why does this work?
Firstly water and oil will not mix – this is because we say that water is a polar molecule, it’s structure means that is has a positive charge one end and a negative charge the other. Water molecules stick together because the positive end of one water molecule is attracted to the negative end of another while oil molecule structure is different – it is non polar meaning that its charge is more evenly spread out, so the oil is not attracted to water, we call it hydrophobic (water fearing) so it tries to get as far away from water as possible and will not mix. The reason that oil rests on top of the water rather than underneath is because it has a different density to water.
As the alka seltzer is added (this is made of citric acid and sodium bicarbonate) it reacts with the water and form carbon dioxide gas and Sodium citrate. It is the bubbles of carbon dioxide that carry the coloured water to the top giving a lava lamp effect.