- In 1797, Louis Vauquelin, a French chemist, discovered chromium.
- The colours of his samples of chromium varied from orange-yellow to orange-red; these samples were a form of lead chromate known as crocodite.
- Crocodite was not readily available in Europe until the early 19th century, when a new source of crocodite was discovered in the Var region of France.
- Within a few years, painters were using the pigment as a dark lemon yellow colour which lasted much longer than the pigments previously available.
- In 1809, Vauquelin carried out a series of investigations to determine the best way of producing crocodite in the laboratory.
- He eventually came up with the following precipitation reaction:
Pb(NO3) 2(aq) + Na2CrO4(aq) 2NaNO3(aq) + PbCrO4(s)
- Or more simply:
Pb2+(aq) + CrO42-(aq) PbCrO4(s)
- Chrome yellow was the first of a range of metal chromates containing lead, barium, strontium or zinc, which can be used to produce pigments with different shades of yellow.
- Chromium yellow is still used today in printing; it is also used to paint the road with double yellow lines!
Useful books for revision
Revise A2 Chemistry for Salters (OCR A Level Chemistry B)
Salters (OCR) Revise A2 Chemistry