PAUL SILVERMAN / FUNDAMENTAL PHOTOS / SCIENCE PHOTO LIBRARY PAUL SILVERMAN / FUNDAMENTAL PHOTOS / SCIENCE PHOTO LIBRARY
Copper complex formation. Three test tubes, demonstrating different stages in the formation of a complex copper ion. The pale liquid at left is copper (II) sulphate. The tube in the centre shows the reaction with the sulphate and ammonium hydroxide; a pale precipitate of copper (II) hydroxide forms at the bottom of the tube. Addition of more hydroxide creates the copper (II) tetrammonium ion, responsible for the deep blue colour seen partially formed in the centre tube and complete in the right-hand tube. This ion is a copper complex, has the formula Cu(NH3)4, and has a double positive charge.
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