17 Copper-Silver Nitrate Reaction In this experiment you will weigh a sample of solid silver nitrate and prepare a water solution of it. You will also weigh a piece of coiled copper wire, place it in the silver nitrate solution, and observe its behavior. By weighing the copper wire at the close of the experiment you will be able to determine the amount of copper reacted. Using these and other measurements you will be able to deter- mine a quantitative relation between reactants and products. In keeping with chemical practice, we will refer to the chemical substances by using appropriate symbols. Copper is an element; it contains only one kind of atom. The symbol for copper is Cu. Silver nitrate is a compound and has the formula AgNO 3 . The symbol Ag is for the silver part and the symbols NO 3 for the nitrate part. The group of atoms NO 3 , consisting of one nitrogen atom and three oxygen atoms, is often found in chemical compounds and has the name nitrate. Before coming to the laboratory, prepare a table in your notebook so that you can record the data you will observe. Use the entries suggested at the end of the procedure section. PROCEDURE a. Obtain a 30 cm length of bare copper wire, It will interact with them.) Fasten the tube in a clean dry 100 ml beaker, an 18 x 150 mm a clamp on a ring stand as shown in test tube, and a vial containing about 3 grams Figure 7-1. Stir the solution with a stirring of silver nitrate crystals. rod to dissolve the crystals and mix the b. Weigh the clean dry beaker, the wire, and solution. Drain the stirring rod by touching the vial containing silver nitrate. Determine the end of the rod to the inside of the test all masses to the nearest 0.01 gram. tube near the mouth. Rinse the stirring rod with a small amount of distilled water into c. Measure about 25 ml of distilled water into the test tube. the test tube. Add the solid silver nitrate from the vial to the water in the test tube. d. Coil the copper wire by wrapping it around Do not rinse or wash the vial. Save it to a glass stirring rod. See Figure 7-2A. be weighed as directed in step f. (Caution ! Stretch the coiled wire as shown in Figure Be careful not to get any of the silver nitrate, 7-2B until it is about 2 cm longer than the solution or solid, on your skin or clothing. test tube. Leave the wire tightly coiled near 18 EXPERIMENT 7 Figure 7-1 Figure 7-3 Test tube containing silver nitrate solution clamped in place. Coiled copper wire placed in silver nitrate solution. one end and stretched out and straightened e. Place the coiled wire into the silver nitrate toward the other. Weigh the wire to ±0.01 solution with the closely coiled end at the gram. bottom of the test tube. Place a one hole Figure 7-2A Figure 7-2B rubber stopper in the test tube with the end of the wire extending through the hole. See Coiled copper wire. Coiled copper wire, stretched. Figure 7-3. Be careful not to shake or in any way disturb the contents of the test tube. Record observations in your laboratory note- book. Allow the reaction to continue for 30 minutes. f. While the reaction is proceeding, weigh the empty vial with cap in order to determine the mass of silver nitrate used in the experiment. g. Shake the crystals from the copper wire. Allow the wire to remain in the solution for a few seconds to see if the reaction is com- plete. Using a wash bottle, rinse the wire EXPERIMENT 7 19 into the weighed 100 ml beaker. See Figure 7-4. Empty the contents of the test tube into the 100 ml beaker. Add a few ml of water to transfer all the crystals from the test tube. Dip the copper wire in acetone, and then set it aside to dry. Weigh the copper wire when it is dry. h. Let the crystals of silver settle in the beaker and carefully decant the solution. Decant means to pour off the liquid, leaving solid be- hind. Pour the liquid along a glass stirring rod as shown in Figure 7-5. Wash the residue three or four times using about 10 ml of dis- tilled water each time. Carefully decant after each washing. A few very tiny particles of silver may float off as you decant. They have a very small mass and may be neglected. After the final washing, the sample must be dried. Your teacher will suggest a suitable method. Be sure to identify your beaker Figure 7-5 uniquely. Decanting the liquid from a solid. j. After the residue is dry, allow the beaker to cool to room temperature. Weigh the beaker containing the product. Make all weighings on the same balance. To make sure the sample is dry, you should subject it to further drying and weigh it again. k. Cover the beaker with a watch glass and save the dry silver crystals. They will be used later in Experiment 8. Your Data Table Should Include the Following: mass of clean dry 100 ml beaker mass of vial, cap, and silver nitrate mass of empty vial with cap mass of the coiled copper wire before reaction mass of the coiled copper wire after reaction mass of the beaker plus silver crystals PROCESSING THE DATA Figure 7-4 1) Determine the change in mass of the Rinsing the copper wire using a wash bottle. copper wire during the experiment. • 20 EXPERIMENT 7. 2) Determine the number of moles of copper 8) Using the results of your experiment, write which reacted. Recall that the mass of a whole number coefficients in the following substance divided by the mass per mole statement : equals the number of moles. One mole of Cu plus mole(s) of 3) Determine the mass of silver obtained. AgNO3 in solution produces mole(s) Ag plus one mole of Cu(NO 3 ) 2 in solution. 4) Determine the number of moles of silver. 9) How many atoms of copper were removed 5) Divide the moles of silver by moles of copper to determine the ratio Ag/Cu. Be from the wire used in your experiment? sure to express your answer as a decimal 10) How many atoms of silver metal were and to the correct number of significant formed in your experiment? figures. A QUESTION TO WONDER ABOUT 6) Determine the moles of AgNO 3 used in the What caused the color in the solution to appear experiment. as the reaction proceeded? 7) Divide the moles of silver by moles of silver nitrate to determine the ratio Ag/AgNO 3 . Express your answer as a decimal using the correct number of significant figures.