ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Chromium hydroxide precipitate formed by adding sodium hydroxide (NaOH) to a solution containing chromium ions. The simplest chromium ion in solution is the hexaaquochromium ion (Cr(H2O)6). When NaOH is added chromium hydroxide (Cr(H2O)3(OH)3) is precipitated out of solution as a pale grey/green solid. Excess NaOH causes a further change to the chromite ion (CrOH6) in a dark green solution. Addition of sodium hydroxide is used as a test for positive metal ions in solution.
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