Lava lamps

The video shows the lava lamp for method 2.

Most methods use Alka Seltzer as it gives the best results. However, here's a couple of methods for making your own lava lamp without Alka Seltzer.

Apparently, Polident (denture cleaning tablets) also work too.You can reuse method two.

Difficulty:

Time: 10-15 minutes plus 10 watching & marvelling

Adult supervision: yes

Dangers: minimal

Objective

To make a lava lamp using chemical reactions and density.

Materials

Container for the lamp: large glass or plastic jar, plastic bottle (i.e. soft drink, water)

Water

Oil (cheap vegetable oil)

Baking soda

White vinegar

Measuring spoons

Small bowl

Food colouring

Dropper or a straw

For method 2:

citric acid (under $3 for a 100g jar) or Alka Seltzer (for a pack of 20 about $8)

Method 1

Put 1 tablespoon of baking soda in the bottom of the jar or bottle (I used a Craig's jam jar).
Pour in warm water until the jar or bottle is 1/4 full.
Mix until all the baking soda is dissolved.
Add the oil until it is about 3 cm from the top.
In a small container, mix 1 tablespoon vinegar with a few drops of food colouring.
Using a dropper or straw, add drops of coloured vinegar to the jar or bottle. It will sink to the bottom and you should see a reaction with the baking soda.

NOTE: the reaction may be quite weak compared to Method 2.

Step 5: mix vinegar Step 6: Add with a

and food colouring dropper

Method 2

Add water to the jar or bottle into it is 1/4 full (I used a 600 ml water bottle).
Add the oil until it is about 3 cm from the top.
Add a few drops of food colouring.
In a small container, mix 1 teaspoon of citric acid and 1 teaspoon of baking soda. Alternatively, use an Alka Seltzer tablet broken into quarters.
Add about 1 teaspoon of the citric acid/baking soda mix or the Alka Seltzer tablets.
You should see a reaction and it should last for about 5-10 minutes. Add the rest of the citric acid/baking soda mix when the reaction slows down.
If you want to store the jar/bottle, make sure the reaction has completely finished before capping.

Left: Step 4 Right: Alka Seltzer tablets

The Science

Lava lamps were invented in 1963 by Edward Craven Walker, founder of an English lighting company. These lamps (left) have a special coloured wax (the orange floating substance) and a clear, water-like liquid enclosed in a glass vessel. An incandescent light bulb heats the wax and its density reduces in comparison to the surrounding liquid. This causes it to rise up through the clear liquid. When the wax reaches the top, it cools and the density increases (compared to the surrounding liquid) and sinks to the bottom.

How do our homemade lava lamps work?

These also work on the principle of density plus an acid-base reaction.

Even though oil is more viscous (thicker) than water, it is less dense. Oil has large molecules compared to water. That is why oil floats on water.

Generic-structure-of-vegetable-oil-conta

Left: structure of vegetable oil. Oils have a glycerol backbone and three fatty acid chains.

Right: the simple H20 structure of water.

In the same volume, less molecules of oil can pack together than water.

The acid-base reaction of the citric acid and baking soda generates carbon dioxide. This forces the coloured water droplets up into the oil. But they fall back to the bottom because they are denser than the oil. Alka Seltzer is comprised of citric acid, sodium bicarbonate (baking soda) and aspirin.