HIGH-SCHOOL CHEMISTRY
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The Compounds of Copper A Project CHARLES H. STONE 144 Wall Street, Orhndo, Florida
PLEASING departure from the routine procedures of many elementary laboratory manuals may be found in starting with a metal ore and working it up into a series of related compounds which display varieties of color and form. For example, take malachite ore. This ore reacts readily with acids and does not call for furnace treatment or other elaborate proredures associated with bomite and chalcopyrite. Malachite ore is a basic copper carbonate, CuCOaCu(0H)z. The pupil is provided with 50 to 100g. of a good quality of this ore which is crushed to powder in a clean, dry iron mortar. The powder is transferred to a flask provided with a two-hole stopper. Through one hole is inserted the stem of a dropping funnel containing dilute sulfuric acid; the other hole receives the short arm of a delivery tube, of which the long arm extends into a bottle containing lime water or some other compound which will form a precipitate with the gas set free in the flask. When all is ready, the stopcock is opened and a small amount of the acid is allowed to fall upon the powder. The escaping carbon dioxide will react with the liquid in the bottle, producing a precipitate. When action ceases more acid is admitted, and so on until it is evident that all of the reacting substance in the powder has been used and only the gangue remains. Avoid excess acid. The precipitate in the bottle is filtered, drained, dried, and saved. The material in the flask is transferred to a flter, the residue washed with a little water and then discarded. The combined filtrate is used as follows: 10 to 15 cc. are placed in a crystallizing dish and set aside in a warm place until crystals form. These will be hydrated copper sulfate. They should be dried on blotting or filter paper and preserved a t once in a tightly stoppered vial or tube, for they effloresce slowly if left exposed to the air. The remaining liquid is divided into two portions. One portion is subdivided into smaller portions to be treated with such precipitating agents as potassium ferrocyanide, sodium phosphate, potassium chromate, etc., to form a number of insoluble colored salts which are filtered, washed, dried, powdered, and preserved in neatly labeled tubes or vials. The second portion is to be converted into the soluble salts of copper. Since the acids of these salts are more volatile than is sulfuric acid it is best to proceed through the carbonate. Add enough sodium carbonate solution to precipitate all the copper; filter, wash, and drain. Preserve a specimen of the copper carbonate. Diviae
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the residue into portions to be treated, respectively, with dilute hydrochloric, nitric, and acetic acids. Filter if necessary. Remember that copper chloride dissolves filter paper, so use shredded asbestos or glass fibers. The liquids are allowed to stand for spontaneous evaporation in a warm place free from dust. The resulting crystals are to be dried and preserved. Do not use heat to dry the copper chloride since it decomposes. Other copper products may also be prepared but the procedure is less simple. Cupromercuric Iodide.-This red powder changes to black at a temperature around 75°C. It is used to paint the bearings of machinery. A black bearing shows that i t is getting too hot. Dissolve 6.8 g. of mercuric chloride in 50 cc. of water. Dissolve 18.3 g. of potassium iodide in 100 cc. of water. Add exactly half of the iodide solution to the mercuric chloride and stir well. Let settle. Decant the clear supernatant liquid. Add the second half of the iodide. The red precipitate will dissolve, forming ReHg14. Now add a concentrated solution of 12 g. of copper sulfate and pass sulfur dioxide into the liquid until a red powder is formed. Filter, drain, dry, powder, and preserve. While copper usually has a valence of two, i t also bas avalence of one, but less often. Cuprous Oxide.-Dissolve 10 g. of powdered copper sulfate crystals in water and add 3. g. of glucose in 150 cc. of water. Heat to boiling and add 7 g. of caustic soda dissolved in 35 cc. of water. Boil for 10 minutes and cool rapidly. Let settle. Pour off the alkaline liquid. Filter off the reddish oxide. Wash, drain, and dry. A clean carbon rod connected to serve as cathode of a direct electric current, with a copper anode, is inserted into a solution of copper sulfate contained in a beaker. Let the current flow until a good deposit of copper forms on the rod. The various specimens of copper and its compounds may now be assembled for an exhibit in such form as the student chooses. Such an exhibit, since it contains many solid substances of different colors and crystalline forms, is sure to arouse interest in the class or in the home. Work of this kind provides an opportunity to vary the usual procedures of the laboratory by furnishing a chance to apply methods and principles previously learned to the solution of a new, different, and interesting problem. The procedures involved are simple, absolutely devoid of danger, and within the capacity of any pupil of ability.
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