VANISH THAT STAIN!

YOU WILL NEED:

Clear plastic tumblers Iodine liquid or tincture (available online) Sodium thiosulphate powder or crystals (available online) Water Safety goggles Rubber gloves

WHAT’S GOING ON?

When mixed in water, iodine swims around as two Iodine atoms bound tightly together. Iodine is blueblack in its solid form but when it is combined with water, the iodine pairs form loose links with water molecule, forming what are called charge-transfer complexes. These water-iodine complexes have a yellow-browny colour. Sodium thiosulphate is known as a ‘reducing agent’ and it forces a negatively charged electron into the iodine duo, causing the iodine atoms to break apart as two negatively charged entities (called iodine ions). The separated iodine no longer interacts with light and so the liquid loses all its colour.

This demonstrates how chemical stain removers remove stains by breaking apart the molecules that are causing the unwanted colourations. Colour-conveying molecules, termed chromophores, can often be torn asunder by either stripping them of an electron (oxidation) or by forcing them to accept an extra electron (reduction). Stain removers are either an oxidising or a reducing agent: household bleach is an example of an oxidising agent, while many carpet cleaners are reducing agents. As a very general rule, synthetic dyes, such as those in brightly coloured soft drinks, are broken apart by reducing agents, while naturally occurring dyes, like the pigments in red wine, are most vulnerable to an oxidising agent.

2. Add a few drops of iodine to the bottom of another tumbler, and half fill with water. Iodine stains, so protect hands and surfaces.

1. Put on safety goggles and rubber gloves. Put a tablespoon of sodium thiosulphate into the bottom of a tumbler. Half fill with water and stir to dissolve.

3. Carefully pour the sodium thiosulphate solution into the iodine. And voilà – the pigment will vanish!