This week, Roy decided to continue with the science theme. The children were fascinated by all the different experiments you can do at home, and Roy wanted to share another home experiment with his online friends. It had to be something the children could easily do themselves, and it had to be safe. It also had to be reasonably tidy - his Grandma didn't want another mess this week. This eliminated a lot of his favourite experiments, but made his decision much easier. The lava lamp in a glass is not only safe and clean, it is a really interesting experiment to watch. So this week, Roy Creates A Mini Lava Lamp In A Glass.
- A clean, clear glass. You don't want it to be decorated because this will make the experiment harder to see. You can also use a glass jar, like Roy did, and then just put the lid on and throw it out when you're finished.
- Cheap vegetable oil
- Water
- Food colouring
- An Effervescent tablet. These are the ones which give off little bubbles when you put them in water. Roy used a denture cleaning tablet because they are cheap and work well, but you can use whatever you like.
Method:
- Pour water into your jar until it is about 1/3 full.
- Add a couple of drops of food colouring of your choice.
- Now, gently pour oil into the glass until it is almost full. You want to leave a little gap at the top, so that it doesn't overflow. About 2 centimetres should do.
- Wait for the oil and water to separate. The oil will float on top of the water. If you poured your oil gently enough, it should only take a few seconds. Roy had lots of bubbles when he finished, so he left the jar alone for about 10 minutes, and they all disappeared.
- Now, break the Effervescent tablet into a few pieces and gently drop them into the glass.
- Wait until they start to fizz and then watch the colourful bubbles rise through the oil.
What Is Happening?
Oil and water don't mix. Why this is so is really beyond the scope of this blog, and I have tried to very simply explain it here. If you are interested in a more scientific discussion of why oil and water don't mix, do an internet search and you will find plenty of pages discussing it. The water is called a polar substance, because it has both a positive and negative charge. The positive charge is on one side of each molecule and the negative charge is on the other. Water works a bit like a magnet, in that the positive end of the molecules will attract the negative end of other molecules - just like a magnet does. This essentially means the water molecules stick together. Oil is a non-polar substance. It has a charge, but its positive and negative charges are more evenly spread out and the water can't find a negative charge to attach to, so it doesn't mix with the oil for very long. Instead, the oil and water separate out. The oil floats on top of the water, because it is less dense (or less heavy) than the water.
When you add the effervescent tablet, you start a chemical reaction. It fizzes and releases little bubbles of carbon dioxide. The gas is lighter than the water and the oil, so it floats up to the top of the glass to escape. When it is floating away though, it surrounds a little droplet of water. With the gas surrounding the water, it momentarily makes the water less dense than the oil, bringing it along. This is why we can see a colourful 'bubble' of water floating through the oil. When the gas hits the top of the liquid though, the gas escapes and the water is suddenly heavier than the oil again, so it drops back down to the bottom of the glass.
You might also notice, if you use denture tablets, that the colour of the water changes. Roy used red colouring, and this changed to purple, then blue, and eventually became 'clear' (though it looked dirty). Why did this happen? Honestly, Roy and I don't know. However, we did notice that the denture tablets contain a lot of oxidizing agents, and we thought they might have something to do with it. If you know the answer, let us know!
