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The Aqueous Chemistry of the Elements$
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George K. Schweitzer and Lester L. Pesterfield

Print publication date: 2010

Print ISBN-13: 9780195393354

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195393354.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 04 December 2021

The Cu Group

The Cu Group

(p.368) 16 The Cu Group
The Aqueous Chemistry of the Elements

George K. Schweitzer

Lester L. Pesterfield

Oxford University Press

The elements of this group, copper Cu, silver Ag, and gold Au, often called the coinage metals, resemble each other in some ways, particularly their tendency to nobility, but it cannot be said that the properties of Ag are intermediate between those of Cu and Au. Even though the d shell is full, the d electrons are active, particularly in Cu and Au. The most stable oxidation states are II for Cu, I for Ag, and III for Au. For Cu, Cu(I) as the simple ion Cu+ disproportionates in HOH, and Cu(III) is so powerfully oxidizing that it is reduced by HOH. Stability may be brought to Cu(I) and Cu(III) only by complexation or insolubility. For Ag, Ag(II) and Ag(III) are reduced by HOH, stability resulting only by forming complex species or insoluble compounds. For Au, the simple Au+ cation disproportionates in HOH, and Au(II) is not known. a. E–pH diagram. Figure 16.1 sets out the E–pH diagram for Cu at a soluble species concentration of 10−1.0 M. It is assumed that there is no complexing agent or any insoluble compound producing agent other than OH− or HOH. Further, almost all species are being considered in their hydrated forms, that is, the forms that they take in the presence of HOH. Oxidation states of 0, I, and II are present. The reddish-orange Cu is a fairly noble metal, and the sole Cu(I) compound is shown as yellow Cu2O since CuOH is unstable. The Cu+ ion does not appear, even though it has been entered in the construction of the diagram. This reflects its strong tendency to disproportionate into Cu(II) and Cu, as predicted by ΔG˚ values. The compound which results when OH− is added to a blue Cu+2 solution is blue Cu(OH)2, not black CuO. Cu+2 is more properly written as Cu(HOH)6+2, and just off to the left of the Cu+2/Cu(OH)2 line, hydrolyzed species like Cu2(OH)2+2 occur. The legend of the figure shows equations for the lines separating the species.

Keywords:   hydroxides, redox reactions

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