These pumpkin lava lamps for Halloween are a fun party activity or decoration and an unusual alternative to a traditional pumpkin. They are super easy to make and entertaining to watch, especially in the dark.
Other ideas are to try different colours, add glitter, or get creative and decorate the jar to look like a witch or ghost.
How to make a pumpkin lava lamp
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
Lava Lamp Instructions
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.
The oil and water will separate into two layers. Water at the bottom and oil on the top.
Decorate as you wish, we used a black white board pen for the face.
Pop in half an alka seltzer tablet and watch what happens.
How do lava lamps work?
Firstly water and oil will not mix – this is because water is a polar molecule. Its structure means that it has a positive charge at one end and a negative charge at the other.
Water molecules are attracted to each other because the positive end of one water molecule is attracted to the negative end of another.
Oil molecules are non polar which means their charge is more evenly spread out. Oil molecules are not attracted to water molecules. They are hydrophobic (water fearing) so try to get as far away from water molecules as possible. The reason that oil rests on top of the water rather than underneath is because oil is less dense than water.
When the alka seltzer ( made of citric acid and sodium bicarbonate) is added it reacts with the water to 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.
More Halloween Science Experiments for Kids
Our spooky lava lamps look great too!
Try one of my great Halloween Science Experiments including jumping ghosts, a spooky noise maker and fake blood.
Or how about giving one of our spooky Halloween STEM challenges a go?
Last Updated on September 28, 2022 by Emma Vanstone