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Synthesis is unique to chemistry. Chemists make compounds, separate them from their reaction mixtures, and then determine their purity. These synthetic procedures had their origins in alchemy and, in their incarnation in modern industry, they have resulted in drugs and materials that have increased our lifetimes and have made our lives more enjoyable. Appropriate synthetic projects for the introductory laboratory should demonstrate some of the characteristics of the synthetic process:
1. the same compound can be made by a number of different synthetic methods,
2. that the separation of the compound depends upon the method of preparation, and
3. that some methods of analysis are more appropriate than others for some compounds.
Students enjoy making compounds, and their enjoyment is proportional to the extent that they have some ownership of the compound--that the compound that they are preparing is theirs.
The preparation and analysis of copper (II) carboxylates has the following advantages:
1. a variety of carboxylates are prepared easily from numerous carboxylic acids,
2. the compounds generally do not need extensive purification,
3. because the compounds contain a colored ion (Cu sup 2+ ) and are decomposed easily by heat, they can be analyzed for copper in two different ways--gravimetrically by decomposition to CuO and by colorimetry, and
4. most of the carboxylates contain water of hydration, which can be determined easily by gravimetric thermal analysis.
Although there are a variety of methods for the synthesis of metal carboxylates, three methods have been used widely for the synthesis of copper carboxylates in aqueous solution:
1. reaction of basic copper (II) carbonate (Cu sup 2+ CO sub 3 (OH) sub 2 ) with a carboxylic acid.
2 RCOOH + Cu sub 2 CO sub 3 (OH) sub 2 --> Cu(O sub 2 CR) sub 2 + 2 H sub 2 O + CO sub 2
2. reaction of the sodium salt of the carboxylic acid with copper (II) sulfate.
2 RCOONa + CuSO sub 4 --> Cu(O sub 2 CR) sub 2 + Na sub 2 SO sub 4
3. reaction of copper (II) acetate with the carboxylic acid in ethanol--water solution.
Cu(O sub 2 CCH sub 3 ) sub 2 + 2 RCO sub 2 H --> Cu(O sub 2 CR) sub 2 +...