Problem 2

Copper(I) oxide

\ce{Cu2O}

is a semiconductor used in solid-state electronics and solar cells. The cubic unit cell has lattice constant

a = 427.0

pm, with oxygen atoms (A) forming a body-centered cubic sub-lattice and copper atoms (B) occupying positions forming a face-centered cubic sub-lattice. (a) What are the coordination numbers of Cu and O? (b) Calculate the shortest

\ce{O-O}

\ce{Cu-O}

, and

\ce{Cu-Cu}

distances. (c) Calculate the theoretical density of stoichiometric

\ce{Cu2O}

in g cm

^{-3}

. (d) A non-stoichiometric sample has

0.2\%

of all Cu atoms oxidized to

\ce{Cu^2+}

. What percentage of Cu sites are vacant, and what is

x

\ce{Cu_{2-x}O}

? (e) Write balanced equations for the reaction of

\ce{Cu2O}

with: (1) atmospheric

\ce{O2}

in humid air; (2) dilute sulfuric acid; (3) hot concentrated sulfuric acid.

Step 5 of 5: Chemical reactions of cuprous oxide

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(1)\; \ce{2Cu2O + O2 -> 4CuO};\quad (2)\; \ce{Cu2O + H2SO4 -> Cu v + CuSO4 + H2O};\quad (3)\; \ce{Cu2O + 3H2SO4 -> 2CuSO4 + SO2 ^ + 3H2O}

Analysis

In moist air $\ce{Cu2O}$ oxidizes to black $\ce{CuO}$ . Dilute sulfuric acid induces disproportionation: $\ce{Cu+}$ is unstable in aqueous acid and splits into insoluble metallic $\ce{Cu}$ and blue $\ce{Cu^2+}$ . In hot concentrated sulfuric acid, sulfuric acid acts as an oxidant, reducing to $\ce{SO2}$ while all copper is oxidized to $\ce{Cu^2+}$ .