Sunday, September 23, 2012

Green Hair

Imagine you are living in a small town in Sweden.
You go to bed one night, naturally blonde.
When you wake up in the morning and look in the mirror your blonde hair has turned green!
Not only that, but your naturally blonde neighbour also has green hair!

This actually did happen in 2011, and, no doubt, caused a certain amount of distress.

Where would you begin in order solve the "green hair" mystery?
What could turn hair green?

Blonde hair often turns green after swimming in chlorinated pool water.
Copper, used in compounds to reduce algae growth in water, can be present in concentrations of about 0.5 ppm in pool water. When bleach (often sold as "liquid chlorine") is added to the pool water it oxidizes the copper resulting in a pretty green colour, and the oxidized copper binds to the proteins in the hair.
If you happen to have copper pipes in your bathroom, you've probably seen "green stains" on the pipes where the copper has been oxidized.

So, back to the story in Sweden.
Samples of drinking water were taken from a number of homes in order to measure the amount of copper present but the concentration of copper in the water did not exceed the recommended guidelines (that is, the copper ion concentration was less than 1 ppm).

However, in new houses, when hot water was left overnight and tested the next morning, the concentration of copper in the water increased dramatically. On further investigation it was discovered that the hot water pipes in new houses lacked the coating that the pipes in older houses had. So, overnight, when the water in the pipes was still and not being continuously "flushed" through the pipes, copper particles were being added to the water.

For solving the "Swedish Green Hair Mystery" Johan Pettersson was rewarded with a 2012 Ig Nobel Prize for Chemistry.


Further Reading 

Suggested Study Questions:
  1. Describe 2 methods you could use to detect the presence of copper ions in water.
  2. Describe the process by which Atomic Absorption Sepctroscopy (AAS) could be used to measure the concentration of copper ions in a water sample.
  3. Describe a way that you could prevent copper from entering the water in the copper water pipes in this Swedish town.
  4. Copper is often present in soils at a concentration of around 50 ppm. What mass of copper would be present in 0.5 tonne of soil?
  5. A particular pool contains 40,000 L of water. If the pool water contains 0.5 ppm copper ions, what is the concentration of copper ions in mol L-1 ?
  6. Chocolate can contain 10 mg/kg  copper. What mass of copper is present in a 250 g bar of chocolate?
  7. Doses of copper that exceed 50 mg/kg of body mass can be lethal. Calculate the mass of copper that would be the lethal limit for an 80 kg adult.
  8. What advice could you give the inhabitants of this Swedish town in order for them to avoid having green hair?

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