Lab Experiment 2: Copper Cycle September 7, 2011

Overview Purpose Safety Precautions Chemical Reactions Experimental Procedure

Purpose Verify and understand the law of conservation of mass. Observe chemical change through a series of chemical reactions. Learn simple measuring techniques. Learn proper handling and disposal of chemicals.

Safety Precautions Wear gloves and safety goggles Careful when handling nitric acid (avoid contact). It can cause burns. Copper metal reacted with nitric acid produces NO 2, a red-brown toxic gas. The whole experiment should be done in the hood. NaOH can cause burns (avoid contact). HCl is toxic by inhalation and corrosive to skin and eyes (avoid contact).

Safety Precautions (cont.) Step 9 (addition of HCl with excess Zn) releases H2 gas, which is flammable. Keep all sources of heat away from this chemical reaction. Acetone is also flammable, so keep away from open flames and other sources of heat. Dispose of chemicals properly.

Chemical Reactions RXN 1: Cu (s)  Cu 2+ (aq) + 2e - RXN 2: Cu 2+ (aq) + 2OH - (aq)  Cu(OH) 2(s) (precipitate) RXN 3: Cu(OH) 2(s) + ∆  CuO (s) + H 2 O (l) RXN 4:CuO (s) + H + (aq) + HSO 4 - (aq)  Cu 2+ (aq) + SO 4 2- (aq) + H 2 O (l)

Chemical Reactions (cont.) RXN 5:Cu 2+ (aq) + Zn (s)  Cu (s) + Zn 2+ (aq) RXN 6:Zn (s) + 2H + (aq)  Zn 2+ (aq) + H 2(g)

Experimental Procedure Mass of a 250 ml beaker? Mass of a 250 ml beaker with ~1 g of copper wire? Place them on a hotplate (turned OFF and in the fume hood). Add 5 ml nitric acid to the copper sample and cover the beaker with a watch glass. Gently heat the mixture until it becomes viscous (turn the hotplate ON to 3).

Experimental Procedure (cont.) When it turns viscous, remove the beaker from the hotplate and allow the mixture to cool. MAKE SURE TO TURN OFF THE HOTPLATE while waiting for the mixture to cool! When the mixture is cool, add 10 ml D.I. H 2 O and stir WITHOUT heat (use magnetic stir bar and turn the stirrer on to 5). Then SLOWLY add 8 ml of 6 M NaOH with continued stirring.

Experimental Procedure (cont.) Carefully add 50 ml D.I. H 2 O to it and heat to boiling for several minutes (turn the hotplate up to 8 or 9). Make sure to avoid splattering of the beaker contents during the boiling process. After any changes appear complete, continue heating for another 5 to 10 minutes. Then remove it from the hotplate.

Experimental Procedure (cont.) Then remove the beaker from heat. Carefully decant the liquid portion into another beaker. Keep the solid! What does ‘decant’ mean? Add 25 ml D.I. H 2 O to the solid residue (then swirl but keep beaker on bench) and make sure to wash the sides of the beaker and decant the water. Do this step one more time. Measure out 30 ml of 3 M H 2 SO 4 and add to the solid and gently heat until all of the solid has dissolved. Remove beaker from the hotplate.

Experimental Procedure (cont.) Crease weighing paper to make an X (and tare) and weigh out no more than 3 g of zinc metal and keep this on the weighing paper. From here, use a scoopula to add SMALL PIECES of Zn to the solution as necessary until the solution becomes colorless (verify by holding a white paper behind the beaker). Swirl the beaker (keep it on the bench) after every addition of Zn. This is when the redox reaction takes place. Decant the solution and keep the solid residue. Add 10 ml of 6 M HCl, which will cause a reaction with Zn 2+. Decant the liquid portion and keep the final product, pure copper.

Experimental Procedure (cont.) Wash the pure copper with 2 portions of 50 ml D.I. water and decant the liquid. Then wash the final copper product with ONE 20 ml acetone (modified) and make sure to also wash the sides of the container, to completely dry the water out. Decant the liquid out and keep the solid product in the beaker. Let it air dry for a few minutes and weigh the beaker containing the copper sample.