# What color light does iodine absorb?

## The answer says yellow but I don't know how...

Feb 19, 2016

The colour absorbed depends on whether the iodine is in a polar or a nonpolar medium.

#### Explanation:

The colour absorbed depends on whether the iodine is in a polar or a nonpolar medium.

What we see

Solid iodine is a deep purple colour.

Iodine vapour and solutions of iodine in nonpolar solvents are also purple.

Aqueous iodine solutions, however, have a yellow-orange colour, because of the formation of a charge transfer complex.

Colour theory (in brief)

When white light strikes an object, some light is absorbed, and some is reflected.

The colours that we see are those that are reflected, and the colours that we don’t see are absorbed by the material.

For example, carrots absorb blue and green light, so we see them as orange.

Iodine absorption

Iodine vapour has a broad absorption with λ_"max" = 540 nm (chartreuse, RGB 129, 255, 0).

Since it absorbs mostly green light, the colour we see is a violet-purple.

Aqueous iodine has λ_"max" = 464 nm (dodger blue, RGB 0, 142 255).

Since it absorbs mostly blue light, the colour we see is orange-yellow.