Writing for Children: Post from the Backyard Experiments blog

Visit www.backyardexperiments.wordpress.com to see this post with its original formatting. Intended for an audience around age 10 or 11 (or their parent/guardian/teacher)

Make your own Lava Lamp

Everyone loves lava lamps. I’ve never met anyone who doesn’t like them. They’re fascinating to watch, and they are absolutely essential to the complete bachelor pad.

With this awesome experiment, you can make your own version!

What you need: a tall clear bottle, water, food dye, vegetable oil or canola oil, and fizzing tablets like Alka-Seltzer (I’m based in New Zealand, so I used these Aspro-Clear pain relief tablets). A funnel is helpful but not necessary.

Steps:

1.  Pour about 4 cm or 2 in of water into the bottle.

2.  Fill the rest of the bottle with veggie oil. This is where the funnel comes in handy! What happens when the oil meets the water?

3.  Add several drops of food dye. Aim the color right at the middle of the surface of the veggie oil. How do the drops of dye behave? Does the color mix with the oil?

4.  Squeeze the bottle and gently tap it against your table or counter to make the drops of food dye mix in with the water at the bottom of the bottle. You can also use a straw or a long stick to mix the color into the water.

5.  Once the color has spread through all the water, remove 2 fizzy tablets from their packaging. You’ll probably need to break them in half so they’ll fit through the neck of the bottle. Drop them into the bottle.

6.  Enjoy the show! Watch how the fizzy tablets affect the colored water in the oil.

Tip: To really make this look like a lava lamp, take it into a dark room and put a flashlight under it.

What’s going on here?

First, the water and the oil don’t mix together. The water is what we call polar, meaning that each water molecule, like the one below, has a positive region (+) and a negative region (-), just like how a magnet has a north and a south.

Oil, on the other hand, is nonpolar. Its molecules don’t have a negative side and a positive side. Polar liquids mix together, and nonpolar liquids mix together, but they don’t mix with each other very well. That’s why you have to shake up salad dressing before you put it on your salad. That’s also why it’s hard to just rinse oil off things with water – you need soap to break it down and wash it away.

Second, the oil has less density than the water. Density refers to how much stuff fits into a certain amount of space. A brick is more dense than a wad of bubble wrap. In this case, a teaspoon of water has more molecules than a teaspoon of oil. It’s the same amount of liquid, but the water is denser than the oil. So the oil floats on top of the water. That’s why you can see those rainbow oil slicks floating on top of puddles on the road when it rains.

As for the food coloring, the dye is both polar and more dense than the oil, so drops of dye float right through the oil without mixing in. But it does mix with the polar, dense water.

Third, when the tablets hit the water, they start fizzing and releasing gas bubbles. The bubbles travel up because the gases inside are lighter and less dense than either the water or the oil. So they go all the way up to the top of the liquid and then burst, releasing the gases. Soda is fizzy for the same reason – carbon dioxide gas is trapped in the bottle or can, and when you open it, the gas is released in bubbles traveling up to the surface. If you drink the soda too fast, the gas might try to go out through your nose or come out as a burp! As the bubbles in the bottle travel up, they each carry a little bit of the colored water with them, which creates the lava lamp look.

Fun Fact: Of all the elements (the most basic substances that make up the universe) the most dense is called osmium. Osmium is a metal very similar to platinum, but it’s too brittle to be used for much of anything. Other very dense elements include gold, lead, and mercury. Liquid mercury is so dense that you can float heavy coins on it!

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