GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY
Copper ion solutions. Left: 0.5M copper sulfate water solution has a blue colour due to copper aquo complex formation ( (Cu(H2O)6)2+ ). Right: after concentrated hydrochloric acid is added to the solution, tetrachlorocuprate complex ( (CuCl4)2- ) is formed and the solution colour changes to green.
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