The Very Colourful Chemistry Quiz

Answer: chlorophyll

The chlorophylls are large organic molecules with a magnesium ion in the middle, a kind of molecule known as a metal complex. There are two different types of chlorophylls; a and b. The two types differ only in the type of side chain attached to one of the carbon atoms in the molecule. Chlorophylls absorb light in the 640-660 nanometre range (in the red region of the visible spectrum) meaning that they appear green or blue-green, which is the complementary colour to red.

Answer: titanium dioxide

Titanium dioxide (TiO2) is a brilliant white, non-toxic solid often used as a pigment in paints. Compounds of lead used to be used as pigments in paint, but have been phased out due to their toxicity. Titanium dioxide is also used in sunscreens and to coat paper.

Answer: carotene

I was surprised to learn that the pigment that gives carrots their orange colour is also responsible for giving oranges their colour, too! Carotene is a large organic molecule that absorbs light at around 450 nanometres (the blue region of the visible spectrum), meaning that it appears orange. Green oranges contain chlorophyll in their skins, but this is gradually lost and replaced with carotene as the fruit matures.

Answer: lawsone

Lawsone is another organic molecule that absorbs visible light, making it coloured. A common feature of all organic molecules that absorb visible light is conjugation - this means that the molecule contains alternating single and double bonds. The more extensive the conjugation, the stronger the absorption.

The "-one" in the name lawsone refers to the presence of ketone (C=O) groups. These are in conjugation with a benzene ring in lawsone, giving an extended conjugated system.

Answer: melanin

Melanin is a dark brown/black pigment also found in skin - the amount determines how dark or light your skin is. Freckles are small concentrations of melanin. Hair also contains another pigment called phaeomelanin, which is a red-brown or yellow-brown colour. The relative amounts of melanin and phaeomelanin in your hair determine its colour.

Answer: indigo

Indigo was originally derived from plants such as woad and gives a rich blue-purple colour when used as a dye. Plant-derived indigo was almost entirely replaced by synthetic indigo in the 20th century. Indigo is now synthesised on an industrial scale beginning from naphthalene (mothballs!).

Answer: lycopene

Lycopene has a very similar structure to carotene, which explains their similar colours. Lycopene is also found in pink grapefruit, guava and watermelon. A number of studies have suggested that lycopene may be a useful cancer-preventative agent.

Answer: chromium 3+

Once again, the wavelength of the light absorbed by the substance in question is what gives it its colour. The inclusion of the metal ion impurities into the alumina structure alter the wavelength of light that is absorbed, and therefore the colour of the stone. Alumina with both iron 3+ and titanium 4+ impurities gives the blue stone known as sapphire, while alumina with iron 3+ impurities gives the amber-coloured stone known as topaz.

Answer: saffron

Crocin is the name of the molecule responsible for the glorious yellow colour that saffron gives to food (such as saffron rice). It's a very large, conjugated molecule with a similar structure to that of carotene. The name crocin derives from the fact that saffron is produced from the crushed stigma of autumn crocus flowers. Centuries ago, saffron was used to dye the robes of Irish royalty.

Answer: carmine

Carmine is a very large metal complex with an aluminium ion at its centre. It is used as a biological stain in medical laboratories. It takes 70,000 insects to produce one pound of carmine! In solution form, it is known as cochineal extract and is used as a food colouring.