7-Copper Cycle Demo [Class Presentation]
Splash Conc. Nitric Acid (25 to 50ml in Hood)
Add a bit water (100-300ml) [green when Cu “coordinated” with NO3 (acid
concentrated) – charge balanced; blue as Cu complexes with water (acid diluted)
and replaces all nitrate – [Cu(H2O)6]2+ complex ion!]
Let penny completely dissolve [use descriptive chem. rules to write equation]
Desc. Rules:
Balanced Redox:
Mention NO2 equilibrium:
Cu + H+ + NO3-  Cu2+ + NO2 + H2O
Cu + 4H+ + 2NO3-  Cu2+ + 2NO2 + 2H2O
2NO2  N2O4 + heat
Cold = Clearer; Hot = Browner (NO2 dominates)  Ask if endo or exo
Pour some brown gas and put in freezer
Pour some brown gas and keep out for comparison
Add 4M NaOH to form blue solid [write equation for formation of solid]
Heat goes to black [use descriptive chem. rules to write equation]
[take notes if waiting – on hot plate]
Put in ice water bath
Add HCl conc. [predict answer with no rules]
Aluminum wire in copper chloride solution overnight [predict answer with no
rules]
Copper Cycle Demo Reactions:
1st : Transistion metal in an oxyacid (see rxn sheet #10)
Have students complete “skeleton rxn” for Cu + HNO3  then balance with half-reactions.
Cu + 4HNO3  Cu(NO3)2 + 2NO2 + H2O
Cu + 4H+ + 4NO3-  Cu2+ + 2NO3- + 2NO2 + 2H2O
Cu + 4H+ + 2NO3-  Cu2+ + 2NO2 + 2H2O (Green solution – it appears that the blue copper complex exists
here as expected together with a high concentration of brown NO2 gas giving an overall green color. This can
be shown by letting a similar sample react completely and swirling to remove any dissolved gas – goes to blue
even without further dilution.)
2nd: Complex Ion Formation (see rxn sheet #9)
Think of this as a transistion metal in excess water (similar to concentrated solutions). This complex already
exists, but diluting emphasizes the complex and slows the production of NO2 gas (less brown emphasizes the
blue).
Cu2+ + 4H2O  [Cu(H2O)4]2+ (blue)
http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Transition-Metal-Ions-in-Aqueous-Solutions1055.html
BUT, continue to simplify as Cu2+ or Cu(NO3)2 (aq) (In fact, the following reactions are all simplifications
and metal complexes make following them in exact descriptive reactions beyond the scope of the course).
3rd: Metathesis Precipitation (see rxn sheet #1)
Cu(NO3)2 (aq) + NaOH (aq)  have students predict and go straight to net ionic. (produces blue solid)
4th: Decomposition (see rxn sheet #13)
5th: Metal Oxide (basic anhydride) in Water (see rxn sheet #7)
heat 
Cu(OH)2  CuO + H2O
(black solid)
cool 
CuO + H2O  Cu(OH)2
(blue solid)
6th: Metathesis Acid Base (see rxn sheet #2)
Cu(OH)2 + HCl  have students predict and go straight to net ionic.
Cu(OH)2 + 2H+  Cu2+ + 2H2O
7th: Single Replacement (see rxn sheet #3)
Cu2+ + Al  have students predict and go straight to net ionic. Comment on metal redox potential sheet.