In the Laboratory
`
`Synthesis and Analysis of Copper Hydroxy Double Salts
`Laura M. Brigandi, Phyllis A. Leber, and Claude H. Yoder*
`Department of Chemistry, Franklin and Marshall College, Lancaster, PA 17604; *claude.yoder@fandm.edu
`
`W
`
`Many naturally occurring, important materials are
`double salts; that is, compounds that can be thought of as a
`combination of two or more simple salts. Several articles have
`been published in this Journal involving copper double salts,
`including the preparation and analysis of basic copper car-
`bonate (1), the preparation and analysis of copper and other
`double salts (2), the purification of basic copper sulfate (3),
`the reaction of malachite with acid (4), and the determina-
`tion of percent copper by colorimetry (5). We report here
`on a project involving the synthesis of several naturally oc-
`curring copper double salts using simple aqueous conditions.
`The ions present in the compound are analyzed using colo-
`rimetric, gravimetric, and gas-analysis techniques appropri-
`ate for the first-year laboratory. From the percent
`composition, the empirical formula of each compound can
`be obtained.
`The mineral paratacamite, Cu4(OH)6Cl2, can be thought
`of as a combination of CuCl2 and Cu(OH)2 in a one-to-three
`ratio—CuCl2[Cu(OH)2]3. It can be prepared by addition of
`hydroxide to aqueous cupric chloride:
`4Cu2+ + 8Cl− + 6OH− → Cu4(OH)6Cl2(s) + 6Cl− (1)
`The two simple salts can combine in a variety of different
`ratios, as shown in Table 1, which also shows that the per-
`centage of copper in the different stoichiometries does not
`vary significantly. However, the chloride percentage varies
`considerably and can be used to determine the stoichiom-
`etry of the compound.
`Four copper hydroxy double salts, the minerals mala-
`chite, Cu2(OH)2CO3; brochantite, Cu4(OH)6SO4; parataca-
`mite, Cu4(OH)6Cl2; and Cu4(OH)6Br2 can be prepared and
`
`tnereffiDrofnoitisopmoCtnecreP.1elbaT
`stlaSedirolhCyxordyHreppoCfoseirtemoihciotS
`tlaSelbuoD
`oitaRtlaSelpmiS
`)%(reppoC
`)%(edirolhC
`uC 5
`)HO(
`2 lC 8
`lCuC4
`)HO(uC1
`10.05
`46.44
`2⭈
`)HO(
`2 lC 6
`lCuC3
`)HO(uC1
`47.05
`75.24
`uC 4
`2⭈
`)HO(
`2 lC 4
`lCuC2
`)HO(uC1
`20.25
`07.83
`uC 3
`2⭈
`)HO(
`2 lC 2
`lCuC1
`)HO(uC1
`77.45
`65.03
`uC 2
`2⭈
`)HO(
`4 lC 2
`lCuC1
`)HO(uC2
`48.75
`15.12
`uC 3
`2⭈
`)HO(
`6 lC 2
`lCuC1
`)HO(uC3
`15.95
`06.61
`uC 4
`2⭈
`uC 5
`)HO(
`8 lC 2
`lCuC1
`)HO(uC4
`65.06
`15.31
`2⭈
`
`2
`
`2
`
`2
`
`2
`
`2
`
`2
`
`2
`
`analyzed by similar methods, allowing a choice of com-
`pounds. The presence of copper, as well as the particular an-
`ion in each compound, can be ascertained by qualitative tests.
`Copper can be identified by formation of the blue–violet
`ammonia complex, carbonate by reaction with acid (fizzing),
`halide by precipitation with silver ion, and sulfate by pre-
`cipitation with barium ion. The presence of the hydroxide
`ion can be determined by IR spectroscopy if desired.
`Quantitative analysis of the compounds involves several
`different procedures. The percent of copper ion can be found
`by colorimetry, using the dark blue color of the copper am-
`monia complex. The percent chloride, bromide, and sulfate
`anions can be determined gravimetrically, and the percent of
`carbonate ion is found by the collection over water of CO2
`gas, evolved on addition of acid. Typical student results for
`this project are given in Table 2 and reveal that the data for
`the percent copper and percent anion can be used to estab-
`lish that, for example, the identity of the compound synthe-
`⭈3Cu(OH)2.
`sized in the paratacamite preparation is CuCl2
`It is unlikely that time constraints will allow each stu-
`dent to do all parts of this project within two laboratory pe-
`riods (the total time for preparation and analysis of one
`compound is three 3–4 hour laboratory periods). The project
`is structured so that it can be broken down in several differ-
`ent ways. One option is to divide students into groups of
`three, with one student doing the synthesis of one compound,
`while a second student is responsible for the copper analysis
`(including preparation of standard solutions), while the third
`is responsible for analysis of the anion. Another option is to
`have each student prepare a compound and then divide the
`analytical work among students, who then share results.
`Clearly, many other permutations are possible.
`
`Hazards
`
`Appropriate eyewear should be worn at all times. Al-
`though copper compounds are generally not very toxic, they
`should be handled with care and all solutions and residues
`disposed of in the appropriate manner. Sodium hydroxide,
`ammonia, and nitric acid are corrosive and must be handled
`with great care, preferably in the hood.
`WSupplemental Material
`Instructions for the students and notes for the instruc-
`tor are available in this issue of JCE Online.
`Literature Cited
`1. Sheeran, D. J. Chem. Educ. 1998, 75, 453–455.
`2. Snavely, F. A.; Yoder, C. H. J. Chem. Educ. 1971, 48, 621–622.
`3. Rodriguez, E.; Vicente, M. A. J. Chem. Educ. 2002, 79, 486–
`488.
`4. Stone, C. H. J. Chem. Educ. 1944, 21, 350.
`5. Yoder, C. H.; Smith, W. D.; Katolick, V. L.; Hess, K. R.;
`Thomsen, M. W.; Yoder, C. S.; Bullock, E. R. J. Chem. Educ.
`1995, 72, 267–269.
`
`tnereffiDrofataDlatnemirepxEdnalaciteroehT.2elbaT
`stlaSnoinAyxordyHreppoCfoseirtemoihciotS
`)%(reppoC
`)%(noinA
`.roehT
`.pxE
`.pxE
`84.75
`85.75
`53.62
`02.65
`20.65
`42.32
`15.95
`94.95
`21.71
`62.94
`85.05
`43.92
`
`dnuopmoC
`
`etihcalaM
`etitnahcorB
`etimacataraP
`uC 4
`
`)HO( 6 rB 2
`
`DS
`22.4
`77.1
`11.1
`51.3
`
`.roehT
`41.72
`42.12
`06.61
`79.03
`
`DS
`58.0
`33.0
`34.0
`92.2
`
`1662 Journal of Chemical Education • Vol. 82 No. 11 November 2005 • www.JCE.DivCHED.org
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