Editing Copper(I) oxide (section)

==Preparation==
Copper(I) oxide may be produced by several methods.<ref name=Ullmann/> Most straightforwardly, it arises via the [[Redox|oxidation]] of copper metal:
: {{chem2|4 Cu  +  O2 →  2 Cu2O }}
Additives such as water and acids affect the rate as well as the further oxidation to copper(II) oxides. It is also produced commercially by reduction of copper(II) solutions with [[sulfur dioxide]]. 

Alternatively, it may be prepared via the reduction of [[copper(II) acetate]] with [[hydrazine]]:<ref>{{cite book|author1=O. Glemser|author2=R. Sauer|chapter=Copper (I) Oxide|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|year=1963|place=NY,NY|volume=2pages=1011}}</ref>
:{{chem2|4 Cu(O2CCH3)2  +  N2H4 + 2 H2O→  2 Cu2O  +  8 CH3CO2H +  N2}}

[[Aqueous solution|Aqueous]] [[Copper(I) chloride|cuprous chloride]] solutions react with base to give the same material.  In all cases, the color of the cuprous oxide is highly sensitive to the procedural details. Cu<sub>2</sub>O degrades to [[copper(II) oxide]] in moist air.

[[File:Cu-pourbaix-diagram.svg|thumbnail|left|[[Pourbaix diagram]] for copper in uncomplexed media (anions other than OH<sup>−</sup> not considered). Ion concentration 0.001&nbsp;mol/kg water. Temperature 25&nbsp;°C.]]

Formation of copper(I) oxide is the basis of the [[Fehling's solution|Fehling's test]] and [[Benedict's reagent|Benedict's test]] for reducing [[sugar]]s. These sugars reduce an [[alkaline]] solution of a copper(II) salt, giving a bright red [[precipitate]] of Cu<sub>2</sub>O.

It forms on [[silver]]-plated copper parts exposed to moisture when the silver layer is porous or damaged.  This kind of [[corrosion]] is known as [[red plague (corrosion)|red plague]].