Try this: The blue bottle experiment

Warning: Sodium hydroxide is a powerful base (the opposite to an acid). Avoid contact with hands and clothes and wash thoroughly in case of contact.

You will need

• water
• sodium hydroxide*
• glucose**
• methylene blue***
• 1 litre container (bottle or glass jar will do). It helps if you can put a stopper or lid on your container.
• 2 teaspoons

*Sodium hydroxide is the active ingredient in Caustic Soda which can be found in the laundry section of your supermarket. It is usually used to unblock drains.

**Glucose can be bought from your chemist. It comes in both powder and tablet form. The powder works the best for this activity. If you buy the tablets, crush them with a mortar and pestle or the back of spoon

***Methylene blue is traditional medication for freshwater aquarium fish. Your local pet store should be able to supply you with some.

What to do

1. Pour 500ml of water into a 1 litre container.
2. Add a heaped teaspoon (approximately 8 grams) of sodium hydroxide and dissolve by swirling.
3. Add two level teaspoons (approximately 10 grams) of glucose and dissolve by swirling.
4. Add 3-4 drops of methylene blue. Swirl the mixture and stop. The liquid should appear blue.
5. Let the solution sit for a while and it should become clear. 
6. Give the flask a few quick shakes so that air dissolves in the solution. If you are using a lid check that it is on properly and take special care not to spill any liquid.
7. The colour will change to blue.
8. This will fade back to a colourless liquid again over a short period of time.
9. The more shaking, the longer the blue colour will take to fade.
10. The process can be repeated for over 20 cycles, you may have to allow more air in if you are using a container with a lid. After some hours, the solution will turn yellow and the colour changes will fail to occur.

Solutions can be flushed down the drain with water.

What's happening?

The blue bottle experiment is an old favourite "chemical magic" demonstration. In the demonstration, a bottle of colourless liquid is shaken for a few seconds until the liquid turns blue. Upon standing for a short period of time, the solution goes clear again. This can be repeated many times.

This is a complex reaction. The simple explanation involves the consumption of dissolved oxygen. The solution is blue to begin with and then becomes colourless as all the available electrons in the mixture are transferred from one substance to another. Shaking restores the blue colour by adding oxygen, which provides electrons, to the mixture.

Just to clarify a few terms:

Electrons are tiny particles moving around outside the nucleus of an atom.

An atom is the basic component of all matter. Everything in the world, including you and I, is made of atoms.

A molecule is two or more atoms joined together by chemical bonds.

By doing this activity you have just demonstrated a redox reaction. This is most fundamental reaction in chemistry. Redox reactions involve the transfer of electrons from one substance to another.

The term 'redox' comes from the two concepts of reduction and oxidation. Reduction describes the uptake of an electron by a molecule or atom. Oxidation describes the loss of an electron by a molecule or atom. These two terms go together, because in a chemical reaction, one cannot occur without the other; electrons lost by one compound must be gained by another. Chemistry students sometimes remember this by using the simple mnemonic device "OIL RIG" - Oxidation Is Loss, Reduction Is Gain.

The bottle contains sodium hydroxide, glucose, water and an indicator called methylene blue. Glucose is a reducing agent that will reduce methylene blue to a colourless form. Shaking the solution provides oxygen which will re-oxidise the methylene blue back to the blue form.

You should also notice that once the mixture has gone colourless, a blue zone remains close to the surface. This is due to oxygen dissolving into the mixture from the air space within the flask.

Applications

Energy is stored and released through redox reactions. Photosynthesis involves the reduction of carbon dioxide into sugars and the oxidation of water into molecular oxygen. The reverse reaction, respiration, oxidises sugars to produce carbon dioxide and water.

Oxidation is part of daily life and can be useful and annoying for people. Useful oxidizing agents are bleaches and antiseptics. Not so useful is the oxidising action of oxygen in the air that can corrode metals. This is known as rust when the metal is iron or tarnish when the metal is copper. When exposed to oxygen most metals will oxidize, although in some cases like aluminium, the oxidised layer then prevents further oxidation.

To view this experiment you can visit these sites:

• Chemistry film studio
• The blue bottle experiment