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CH 103: A SERIES OF CHEMICAL REACTIONS,THE COPPER CYCLE • The word chemistry was most likely taken from the Greek χημεία (chemeia) which means to pour metals together. • A chemist studies the transformations of matter at the atomic and molecular scales. • “The Discovery of Phosphorus” was painted by Joseph Wright of Derby in 1771. • Phosphorus was discovered by Hennig Brand in 1669.
STEP #1: PREPARATION OF Cu(NO3)2 FROM Cu • Accurately weigh 0.5 grams of copper wire to 3 significant digits. Record this mass in your data sheet. For example, this wire might weigh 0.512 g. • Perform the rest of this step in a FUME HOOD. • Place the Cu wire in a 250 mL beaker and CAREFULLY add 10 mL of 16 M (concentrated) nitric acid (HNO3). The copper wire should begin to dissolve almost immediately. If necessary, carefully warm the reaction mixture on a hot plate. • The blue color is due to copper(II) nitrate (Cu(NO3)2) and the brown fumes are nitrogen dioxide (NO2). • Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l) • The reactant, Cu metal. The product, Cu(NO3)2.
STEP #1: PREPARATION OF Cu(NO3)2 FROM Cu • Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l) • This is an oxidation-reduction reaction. That is, electrons are transferred from 1 reactant to another reactant. • Oxidation is a loss of an electron or electrons by an atom or group of atoms. • Reduction is a gain of an electron or electrons by an atom or group of atoms. • In this reaction, Cu(0) is oxidized to Cu(II), and N(V)O3- to reduced to N(IV)O2.
STEP #2: PREPARATION OF Cu(OH)2 FROM Cu(NO3)2 • Dilute your solution to 100 mL with distilled water. • You may now move from the fume hood to your laboratory bench. • Cautiously add 30 mL of 6 M (dilute) sodium hydroxide (NaOH) to this solution. • Use a stirring rod to transfer a drop of this solution to a piece of red litmus paper. This litmus paper will turn blue in a basic solution. If it is not basic, add more 6 M (dilute) NaOH until the solution turns red litmus paper blue. • The products of the reaction are the pale blue solid copper(II) hydroxide (Cu(OH)2) and a colorless solution of aqueous sodium nitrate (NaNO3). • You will use any changes in color and solubility to write a balance equation for this reaction.
STEP #3: PREPARATION OF CuO FROM Cu(OH)2 • Use a Bunsen burner to carefully heat your blue Cu(OH)2 solution until it is converted to a mixture of black CuO and H2O. • Stir constantly when heating. • Do NOT let the mixture boil vigorously. • This process should take about 5 minutes. • The product, CuO. • You will use any changes in color and solubility to write a balance equation for this reaction.
STEP #4: PREPARATION OF CuSO4 FROM CuO • Let the CuO settle. • Carefully decant and discard the liquid. • Use a Bunsen burner to heat 200 mL of distilled water. • Use approximately 1/3 of this very hot distilled water to rinse your CuO. Then discard this rinsate. Repeat this process until all of the 200 mL of distilled water is gone. This is called the method of successive dilutions. It is used to remove any residual nitrate that might be leftover from Step #1. If you do not do this your yield of copper will suffer. • Add 15 mL of 6 M (dilute) sulfuric acid (H2SO4) to the CuO. If necessary, add more H2SO4 until all the black CuO has dissolved to yield a blue solution of copper(II) sulfate (CuSO4). • The product, CuSO4. • You will use any changes in color and solubility to write a balance equation for this reaction.
STEP #5: PREPARATION OF Cu FROM CuSO4 • Add 2 g of zinc (Zn) metal to the CuSO4 solution. Stirring occasionally until the solution becomes colorless. Adding more Zn will quicken this process; however, adding too much Zn should be avoided because it will have to be removed later. • The beaker has both Cu and Zn metal. Add 10 mL of distilled water, 8 mL of 6 M (dilute) hydrochloric acid (HCl), and stir to dissolve the excess Zn. Gently warm this solution with a Bunsen burner to speed up the dissolution of Zn. • Hydrogen (H2) gas is evolved as follows: • Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) • (This is another example of an oxidation-reduction reaction.) • The reaction is done when the bubbles of H2 gas stop. • When this reaction is done, let the solid Cu settle and decant the liquid. • Use two 50 mL aliquots of distilled water to rinse the Cu. Discard the rinsate. Be careful not to lose any Cu.
STEP #6: DRYING Cu METAL • Record the weight of an evaporating dish. • Use a rubber policeman to transfer the Cu metal and as little water as possible to the weighted evaporating dish. • Use a boiling water bath to gently dry the sample. • Do NOT heat the Cu to dryness in flame. The Cu will react with air to make CuO. • Let the evaporating dish to cool to room temperature. • Record the combined weigh of the dish and Cu.
SAFETY • Give at least 1 safety concern for the following procedures that will be used in today’s experiment. • Heating glass with a hot plate or a flame. • Injury from a burn or causing a fire. Be careful. Do not wear loose clothing or long hair. Glass can shatter when heating; wear your goggles at all times. • Using 16 M HNO3, 6 M NaOH, 6 M H2SO4, 6 M HCl, and Zn. • These are irritants. Wear your goggles at all times. Immediately clean all spills. If you do get either of these in your eye, immediately flush with water. • Generating H2O(g) and acidic gases. • Again, these are irritants. Wear your goggles at all times. Use the fume hood when handing 16 M (concentrated) HNO3. Immediately clean all spills. If you do get either of these in your eye, immediately flush with water. • Your laboratory manual has an extensive list of safety procedures. Read and understand this section. • Ask your instructor if you ever have any questions about safety.
SOURCES • Amethyst Galleries, Inc. 2006. Copper (Cu). http://www.galleries.com/minerals/elements/copper/copper.htm Available: [accessed 18 September 2006]. • Barnes, D.S., J.A. Chandler. 1982. Chemistry 111-112 Workbook and Laboratory Manual. Amherst, MA: University of Massachusetts. • Hong Qing Chemcial. 2006. Copper Sulfate Pentahydrate. http://www.hongqingchem.com/copper2.htm Available: [accessed 18 September 2006]. • Joseph Wright of Derby. 1771. The Discovery of Phosphorus. • JunCheng International. 2006. Copper(II) nitrate, trihydrate. http://www.czlthg.com/web/2/index43.htm Available: [accessed 18 September 2006]. • JunCheng International. 2006. Copper(II) oxide. http://www.czlthg.com/web/2/index44.htm Available: [accessed 18 September 2006]. • Unknown. 2006. Etymology of Alchemy. http://en.wikipedia.org/wiki/Chemistry Available: [accessed 18 September 2006]. • Weast, R.C, M.J. Astle, W.H. Beyer. 1983. CRC Handbook of Chemistry and Physics. Boca Raton, FL: CRC Press, Inc.