What is the (II) beside copper of copper(II) hydroxide?

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ncchemist eNotes educator| Certified Educator

Copper (II) hydroxide is Cu(OH)2.  It is also called cupric hydroxide.  The Roman numeral II denotes the level of positive charge on the copper cation.  Hydroxide (OH) always has a -1 charge, so the two of them are negated by the +2 charge on the copper to make a neutral compound.  Copper as a transition metal can form two different cations, Cu+1 and Cu+2.  The Roman numeral is used to distinguish between the two different possible cations.  If we were talking about CuOH, then the chemical name would be copper (I) hydroxide to denote a +1 charge on the copper.