Experiment 5: Preparation of Copper(I) Chloride, CuCl
8 September 2015
Goal: To prepare copper(I) chloride by reducing copper(II) chloride with sulfite ions in the
presence of chloride ions.
Objectives: At the end of this session students should be able to:
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Isolate and store inorganic compounds with unstable oxidation states
Discuss the relative stability of Cu(I) and Cu(II) ions
Predict the structures of ionic salts like Cu(I) chloride and Cu(II) chloride from radius
ratio rules
Suggest why radius ratio rules sometimes fail to accurately predict the structure of
ionic crystals.
Theory
Copper can exist as Cu(I), Cu(II) which is most common and Cu(III) which is rare. The
relative stabilities of each oxidation state depend on the nature of ligands and anions as well
as the nature of the solvent medium. In the experiment below the copper(I) ions once formed,
react with chloride ions to form the insoluble copper(I) chloride.
The relevant redox potentials are:
Cu+ + e- ↔ Cu(s)
E° = 0.52 V
Cu2+ + e- ↔ Cu+
E° = 0.15 V
Cu2+ + 2e- ↔ Cu(s)
E° = 0.34 V
Hence Cu(s) + Cu2+ ↔ 2Cu+
E° = -0.37 V
Method
WARNING! Glacial acetic acid is a dangerous liquid and must be used in a fume
cupboard.
Prepare three solutions:
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(a) dissolve sodium sulfite (2.5 g) in 13 cm3 of water,
(b) dissolve copper(II) chloride dihydrate (3.3 g) in 7 cm3 of water,
(c) prepare a sulfurous acid solution by dissolving sodium sulfite (0.3 g) in 250 cm3 of
water and add 3 cm3 of 2 M hydrochloric acid,
Add slowly, with constant stirring, the sodium sulfite solution to the copper(II) chloride
solution. Dilute the suspension of copper(I) chloride so formed with about half the sulfurous
acid solution, allow the precipitate to settle, and decant most of the supernatant solution.
Filter the solid by suction on a Buchner funnel or sintered glass crucible (fumehood) and
wash it into the funnel by means of the sulfurous acid solution. Take care that the copper(I)
chloride is always covered by a layer of solution. Finally, wash the product with 5 cm3 of
glacial acetic acid and 10 cm3 of ethanol and dry it in air, or in a vacuum desiccator.
Determine and record the yield.
Immediately show the product to a demonstrator for grading. Store in a stoppered bottle and
label with your name, formula of compound and yield.
Write a balanced chemical equation for the preparation and calculate the % yield based on the
quantity of copper(II) chloride hydrate used.
Note that both CuCl and CuCl2 have crystalline ionic lattice structures. The structure of an
ionic salt depends on the relative sizes of the ions that form the solid. The relative sizes of
these ions is given by the radius ratio, which is the radius of the positive ion divided by the
radius of the negative ion.
If the assumptions of an ionic model hold then the structures of the ionic crystal can be
rationalized based on the radius ratio rules shown below:
Radius
Ratio
CN
Holes in Which
Cations Pack
0.155 0.225
3
triangular holes
0.225 0.414
4
tetrahedral holes
0.414 0.732
6
octahedral holes
0.732 - 1
8
cubic holes
1
12 close-packed structure
Note: The lower limit in each range is the ideal ratio and is known as the LIMITING
RADIUS RATIO. The text-book and this link to the Univ of Sydney might be useful for
additional information on the calculation of the radius ratios.
Below 400 °C CuCl has the zinc blende structure (ccp) but above this temperature it converts
to the wurtzite structure (hcp). CuCl2 has a CdCl2 type structure (ccp).