Reactions of hexaaquacopper(II) ions with ammonia solution
The reaction of hexaaquacopper(II) ions with carbonate ions
An undergraduate chemistry laboratory project involving the synthesis of [Ag(NH3)2]2SO4 and Cu(NH3)4SO4 from the simple sulfate salts is described. Characterization of the stoichiometry of the complexes is accomplished by gravimetric and volumetric analysis. Silver is precipitated as the chloride and copper is precipitated as the hydroxide and converted to the oxide before weighing. The ammonia content of each complex is determined with a back titration using dilute nitric acid and sodium hydroxide. Typical student work gives results for the stoichiometry of the complexes within 1-5% of the theoretical values. The project provides a convenient preparation of two compounds whose identity and formula will not be obvious to the student. The analytical procedures illustrate the fundamentals of gravimetric and volumetric analysis and some basic characteristics of simple coordination complexes. The analytical data allow the student to determine the identity of each product by determining its empirical formula.
The reaction of hexaaquacopper(II) ions with iodide ions
Although our primary focus in this unit is on bonding, the topic of coordination complexes is so important in chemistry and biochemistry that some of their basic features are worth knowing about, even if their detailed chemistry is beyond the scope of this course. These complexes play an especially crucial role in physiology and biochemistry. Thus heme, the oxygen-carrying component of red blood cells (and the source of the red color) is basically a complex of iron, and the part of chlorophyll that converts sunlight into chemical energy within green plants is a magnesium complex.
Investigation of Copper(II) amino acid complexes
If you have taken a lab course in chemistry, you have very likely admired the deep blue color of copper sulfate crystals, CuSO4·5H2O. The proper name of this substance is copper(II) sulfate pentahydrate, and it is typical of many salts that incorporate into their crystal structures. It is also a , a term used by chemists to describe a substance composed of two other substances (in this case, CuSO4 and H2O) each of which is capable of an independent existence. The binding between the components of a complex is usually weaker than a regular chemical bond; thus most solid hydrates can be decomposed by heating, driving off the water and yielding the salt:
To synthesize a Copper(II) oxalate complex 2
Driving off the water in this way also destroys the color, turning it from a beautiful deep blue to a nondescript pale yellow. If the anhydrous salt is now dissolved in water, the blue color now pervades the entire solution. It is apparent that the presence of water is somehow necessary for the copper(II) ion to take on a blue color, but why should this be?