So having had a few unsuccessful experiments recently I needed a sure fire one, and this was it. It’s a fun one for kids to help set up. Kid M is 4 (just) and was a pretty good lab assistant with the pouring, squeezing and mixing. I wouldn’t say she was particularly wowed by the results (although she was having a bit of an ‘off’ day shall we say…), but did enjoy spotting the bubbles. However, I found watching it quite nicely relaxing and it did the job keeping us entertained for about half an hour. So not a bad result in the end!
What you need:
- Glass or jar (essential – any shape will do but tall and thin probably best)
- Oil (essential – we used olive but am sure you can use vegetable, sunflowers etc)
- Washing up liquid (essential – just used some super cheap stuff)
- Water (essential)
- Food colouring (not essential but as always makes it look pretty).
What to do:
- Fill the glass up half way with water and stir in food colouring.
- Pour oil on top, about a cm or two, and wait until it has settled (it should be separate to the water and sitting on top of it).
- Drop washing up liquid into the glass and watch what happens.
- We used the gel variety of food colouring but I would actually recommend good old fashioned liquid stuff as I think it would work better. Also it’s good to use a colour that is different to your oil and washing up liquid (green and yellow were not great for this reason).
- Mix it all up at the end and see what happens. If you do it in a jam jar then you can just pop the lid on and shake.
The science bit
The water and oil don’t mix initially because they are immiscible. This basically means they don’t blend together when mixed, due to the water molecules being more attracted to each other than to oil molecules.
The drops of washing up liquid sink, pushing the oil down underneath them. However the oil is less dense than the washing up liquid and the water, so it escapes and rises to the surface. Density is how heavy and how spread out the molecules are in a substance. The less dense liquid floats, in this case the oil.
Mix them all up at the end and the mixture should eventually become one colour. The washing up liquid attracts both the water and the oil, which allows them to mix together forming an emulsion.
Explaining it to children
Water and oil don’t mix together. Basically the water wants to stay with other bits of water, and the oil wants to stay with the oil. The water also pushes the oil to the top of the glass. The washing up liquid sinks when it is dropped in and pushes a bit of oil down with it. However the oil wants to be at the top so bubbles of it float up again when it can get free from the washing up liquid. When you mix them all together the washing up liquid happily mixes with both the oil and the water, and so the oil and the water mix together too.
Experiment based on an activity from the fantastic Usborne Activities: 365 Science Activities book.