Lava Lamps

This week we are going to make our very own lava lamps!

lava lamp

 

You will need…

  • A clear plastic bottle – I used an old 2L Cola bottle (washed up of course)
  • A bottle of vegetable oil
  • Water
  • Alka Seltzer
  • Food colouring (a bright colour is best!)

Method

Fill the bottle a quarter full with water. Top up to the (near) top with the vegetable oil.

The oil and water should separate into two layers, water at the bottom and oil on the top.

Add about 6-8 drops of food colouring once they have separated. The colour will mix with the water at the bottom.

Pop in half an alka seltzer tablet and watch the bubbles form. Add more alka seltzer bit by bit to keep the bubbles rising and falling.

Your lava lamp can be used over and over again.

lava lamp

The Science bit

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.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 – in fact 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 carbon dioxide bubbles that carry the coloured water to the top.

There are 25 comments

  1. Suzette

    I did this in the fall and plan to do it again with my group in the spring. I don’t know who was more excited, the children the parents or myself. It’s a great way to bring science into the classroom for preschoolers. Even though the excitment for the 2 &1/2 year old wore off after the bubbles stopped, needless to say he enjoyed that part.

  2. Actually Mummy...

    Must give that one a try! Thanks for the linky – I must admit mine has been flogged around a little bit, but it is a good one, and I’ve never flogged it here before! Will try to be a bit more creative next time 😉

  3. Ticia

    I’ve seen someone do a similar one with layering liquids and that one looked impossible. This actually looks doable and fun. Now would I remember to actually pick up alka-seltzer?

    Thanks for linking up to Science Sunday!

  4. Tabitha Carri

    Hi! I love the lava lamp idea and that it involves recycling! I linked to it in a recent post at The Green Classroom blog. If you do not wish to be in this post, just let me know, and I will remove it. You can check out the post here – Your Green Classroom

    Thanks a bunch!

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