Jacob Stephens, Will Heffern
Department of Biology
255 Grapevine Road, Wenham Massachusetts, 01984; [email]
1. Chemicals and materials
Copper wire and sand paper were purchased from Home Depot (Danvers, MA). Nitric acid (HNO3) (conc.), sulfuric acid (H2SO4), 3.0 M sodium hydroxide (NaOH), and evaporating dishes were obtained from Fisher Scientific (Pittsburgh, PA). The boiling chips were obtained from Acros Organics (Geel, Belgium). Zinc powder was obtained from Alfa-Aesar (Ward Hill, MA). Acetone was obtained from Pharmco (Brookfield, CT). 18 MΩ Millipore grade deionized water was used.
2. Copper redox reaction with nitric acid to form copper nitrate, water, and nitrogen dioxide
Cu(s) + 4HNO3(aq) Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
Sandpaper was used to clean an approximately 0.500 g strip of #16 copper wire. Then the mass of the wire was measured to the nearest 0.0001 g with a digital scale and recorded. The wire was then placed into a 250 mL beaker. The beaker was then placed under the hood to have two plastic-pipets-full (about 5 mL total) of concentrated nitric acid (HNO3) added. The copper immediately began to react with the nitric acid and was kept under the hood until the reaction completed. Then beaker was transferred to the laboratory bench and had 100 mL of deionized water added.
3. Copper nitrate double replacement reaction with sodium hydroxide to form copper hydroxide and sodium nitrate
+ 2NaOH(aq) Cu(OH)2(s) + 2NaNO3(aq)
Next, 30 mL of 3 M sodium hydroxide (NaOH) was added to the solution in the beaker.
4. Copper hydroxide decomposed by heat to form copper and water
Cu(OH)2(s) CuO(s) + H2O(l)
Two boiling chips (three would have worked as well) were then added to the solution. The solution was then carefully heated until it just began to boil while being stirred with a stirring rod.
5. Copper oxide double replacement reaction with sulfuric acid to form copper sulphate and water
CuO(s) + H2SO4(aq) CuSO4(aq) + H2O(l)
The black solid formed by the previous reaction was allowed to settle, and then the supernatant liquid was decanted. 200 mL of nearly boiling deionized water was then added. The solution was stirred, and then the solid was again allowed to settle. The solution was decanted again. Next 15 mL of 6 M sulfuric acid (H2SO4 (aq)) was added.
6. Copper sulphate and sulfuric acid single replacement reaction with zinc to form zinc sulphate, copper, and dihydrogen
CuSO4(aq) + Zn(s) ZnSO4(aq) + Cu(s)
The boiling chips were removed with tweezers, and then the beaker was taken back to the hood. 2.0 g of 40-mesh zinc metal (Zn(s)) was added. A redox reaction between the Zn(s) and excess H2SO4 took place in the beaker after the Zn(s) was added.
7. Isolation of copper
After the zinc dissolved and the supernatant liquid became clear, two drops of concentrated ammonia were added to test for Cu2+(aq), and a blue complex was formed. The solution was then heated gently to ensure that the zinc was completely dissolved, the the solution was allowed to cool.
As the solution was cooling, a porcelain evaporating dish was weighed. When the solution cooled and precipitated copper settled to the bottom of the beaker, the supernatant was decanted and the copper transferred to the porcelain evaporating dish. The precipitate was washed with 5 mL deionized water, allowed to settle, and then the liquid decanted. The washing process was repeated. Acetone was used as the final washing solution.
After the second washing, the copper sample was dried. When the copper sample dried, the copper was discarded into the hood.