Chemical Reactions of Copper Lab
Tara Faggioli Pd. 5 10/19/09
Introduction In this lab, solid copper metal is going to be reacted through a series of reactions using the
cation Cu+2. In order to be sure a reaction has actually taken place, a precipitate or gas will be formed, there will be a significant temperature change, or a color change will occur. At the end of the lab, the copper will be precipitated and compared with the starting point to try and verify the Law of Conservation of Mass. Theory The Law of Conservation of Mass states that matter cannot be created nor destroyed. Our
lab is set up to help prove this theory by starting with a set mass of copper, reacting it in excess solutions, and then precipitating the copper back out and comparing the start and end masses. For For part part A, copp copper er (II) (II) nitr nitrat ate e form formed ed from from soli solid d copp copper er meta metal. l. The The bala balanc nced ed oxidation oxidation-redu -reduction ction reaction reaction is Cu (s) + 5HNO3(aq) -> 2NO2(g) + Cu(NO3)2(aq) + 2H2O + H+. Nitrogen dioxide, NO 2, is toxic and must be collected under a fume hood, and it also is a very strong strong oxidiz oxidizing ing agent. agent. There There are many many differ different ent uses uses for copper copper (II) (II) nitrat nitrate, e, Cu(NO Cu(NO 3)2, among them being being for light-sen light-sensiti sitive ve papers, papers, insectici insecticide de for vines, vines, electroplating electroplating,, and in paints. For part B, copper (II) hydroxide was made from the copper (II) nitrate. The balanced double displacement reaction is Cu(NO 3)2(aq) + 2NaOH(aq) -> Cu(OH)2(s.aq) + 2NaNO3(aq). The net ionic ionic reacti reaction, on, includ including ing the slight slightly ly solubl soluble e copper copper hydrox hydroxide ide,, is Cu +2(aq) + 2OH-(aq) -> Cu(OH)2(s.aq). Copper hydroxide, Cu(OH) 2, can be mixed with latex paint to make a product that that contro controls ls root root growth growth in potted potted plants plants.. Sodium Sodium nitrat nitrate, e, NaNO3, is an ingr ingred edie ient nt in fertilizers, pyrotechnics, pyrotechnics, a rocket propellant, and glass and pottery enamels. For part C, copper copper (II) oxide oxide came came from from the copper copper (II) (II) hydrox hydroxide ide through through the balanced double displacement reaction Cu(OH) 2(s) + H2O(l) —-> CuO (s) + 2H2O(l), with the net ionic ionic being being the same. same.
Copper Copper (II) oxide, oxide, CuO, CuO, can be used to dispos dispose e of hazardou hazardous s
materials, including cyanide, hydrocarbons, and dioxins through oxidation. It is also used as a pigment in ceramics, producing blue, red, and green, and sometimes gray, pink, or black glazes glazes.. Occasi Occasiona onally lly,, CuO is used used as a dietar dietary y supple supplemen mentt in animal animals s agains againstt copper copper deficiency. In addition, it is used in dry cell batteries and some wet cell batteries as the cathode (using lithium as an anode). For part D, the copper (II) oxide reacted with sulfuric acid to produce copper (II) sulfate. The balanced double displacement reaction is CuO (s) + H2SO4(aq) -> CuSO 4(aq) + H2O(l). The net ionic reaction excludes the copper because it would be written as 2H
+ (aq)
+ OH-(aq) ->
H2O(l). However, this is useful to us because we are then left with only copper sulfate in our beaker. Copper sulfate, CuSO 4, is apparently extremely useful. In can be used as a herbicide, fungicide, a pesticide, and an analytical reagent along with being used in organic synthesis,
and being included in many beginner chemistry sets. Previously, copper sulfate was used as an emetic, but it is now considered considered too toxic for this use. One artist, Roger Hiorns, filled filled a flat with copper sulfate, allowed it to crystallize for several weeks, then drained off the extra water to reveal blue crystal-coated walls and floors. The work is titled Seizure. For part E, zinc was added to the copper sulfate to regenerate the copper metal in the balanced oxidation-reduction reaction Zn (s) + Cu+2(aq) -> Zn+2(aq) + Cu(s). The excess zinc was then dissolved out with hydrochloric acid in the single displacement reaction Zn
(s)
+
2HCl(aq) -> ZnCl2(aq) + H 2(g), net ionic reaction of 2H +(aq) -> H 2(g). At this point, the copper from part A has been retrieved and the compound is rinsed with methanol and acetone to ensure the other ions will not reappear once the liquid is dried off. A stoichiometry problem relies on the balanced reactions. Using stoichiometry, you can calculate how much of a product you can expect to yield based on how much reactant you start start with. with. Every Every problem problem uses uses a mole mole to mole mole ratio ratio of compound compounds s based based on the coefficients of the reaction. A percent yield calculation is used to determine how much of product you made compared with how much you expected to make. This is done by first doing a stoichiometry problem to calculate how much reactant you should have formed, then divide the amount of product you actually formed by the amount of product you should have formed and multiply by 100 to get a percent. Materials and Procedure 250mL Erlenmeyer balance copper deionized water 16M nitric acid tongs
hot plate 6M sodium hydroxide red litmus paper stirring rod beaker drying oven
zinc metal evaporating dish 12M hydrochloric acid acetone methanol
Part A: Weigh an Erlenmeyer and add 1.00g copper metal to it. Put the flask under the fume hood and add 5mL nitric nitric acid. Use tongs to swirl on a hot plate and drive off all the gas by holding the flask at an angle since the gas is denser than the air. Allow to cool. Part B: Add 50mL deionized water to the copper (II) nitrate solution, then slowly add 6M sodium hydroxide and swirl between each addition. Add until red litmus paper turns blue. Rinse sides first and use a stirring rod to put the solution on the paper. Part C: Transfer to beaker and gently warm with a hot plate. Allow the precipitate to settle and decant. Heat 200mL deionized water. Wash the copper oxide with the warm water. Allow it to settle and decant again. The compound should be washed twice. Part D: Add 15mL 6M sulfuric acid and swirl until everything is dissolved.
Part E: Add 3.5g zinc metal to the beaker, swirling until the liquid is colorless. Stir in 20mL 12M hydrochloric acid to dissolve any remaining metal. Add another 5mL of acid if the metal still isn’t dissolved. Pour off the liquid and wash with 20mL deionized water. Transfer the copper to a pre-weighed evaporating dish and wash with 10mL methanol. Decant the liquid carefully so none of it touches your skin, and then rinse with acetone and decant. Place the evaporating dish in the drying oven. Once the liquid is evaporated off, weigh the dried copper to compare with the starting amount. Data and Observations Mass of evaporating dish and copper (end) Mass of evaporating dish (empty) Mass of flask and copper (start) Mass of flask (empty) Mass of copper (start) Mass of copper recovered % recovery of copper
27.87g 26.71g 80.58g 79.62g .96g 1.16g 120%
Calculations: Mass of copper (start) 80.58g – 79.62g = .96g Mass of copper (end) 27.87g – 26.71g = 1.16g % recovery of copper 1.16g / .96g x 100 = 120% % error |.96 – 1.16| / .96 x 100 = 20% Questions: 1. A. Copp Copper er (II) (II) nitrat nitrate e - Cu(NO Cu(NO3)2 – blue B. Copper (II) hydroxide – Cu(OH) 2 – pale blue C. Copper (II) oxide – CuO – black D. Copper (II) sulfate – CuSO 4 – blue E. Copper metal – Cu – “pinkish,” “peachy,” also metallic, “orangish,” slightly “brownish” –> just think of a penny and you’ve got it. A clean, shiny penny. =D 2. Consid Consideri ering ng our percent percent error error of 20%, 20%, I’d say we overshot overshot the Law of Conserv Conservati ation on of Mass just a bit. Possible sources of error besides human ones include a bit of greenishbluish precipitate remaining when we weighed the copper and weighing dish for the final mass, or excess reactants not being fully washed off or reacted away at any other point. Observations: A. B. C.
D. E. Summary
Post-lab Questions 1. Redox: Redox: Cu + NO3NO3- -> Cu+2 Cu+2 + NO
red: (4H+ + 3e- + N (+5)O3- -> N(+2)O + 2H2O)2 ox: (Cu(0) -> Cu+2 + 2e-)3 combined: 8H+ + 6e- + 2NO 3- + 3Cu -> 2NO + 4H 2O + 3Cu+2 + 6esimplified: 8H + + 2NO3- + 3Cu -> 2NO + 4H 2O + 3Cu+2 double displacement: CaCl 2(aq) + Na2CO3(aq) -> CaCO3(s) + 2NaCl(aq) 2. A double displace displacement ment reaction reaction occurs occurs when a solid solid (precipitat (precipitate), e), gas, or a liquid liquid is formed. Two aqueous products haven’t really been reacted because most double displacement reactions happen in solution to start with, and compounds in solution break up into ions. 3. Generally, Generally, percent percent yield yield is the percent percent value of how much much product product is formed formed from a certain amount of reactant. The maximum value a percent yield can have is 100%. Percent yield added to percent error equals 100. 4. reac reacti tion on:: Cu Cu(s) + 5HNO3(aq) -> 2NO2(g) + Cu(NO3)2(aq) + 2H2O + H+ 1.00gCu x 1molCu/63.55gCu x 1molCu(NO 3)2/1molCu x 185.75gCu(NO 3)2/1molc = 2.95g 1.40g/2.95g x 100 = 47.5% yield 5. a. S + O2 -> SO2, 98.0% yield .980(1.00kgS x 10 3gS/1kgS x 1molS/32.07gS x 1molSO 2/1molS) = 30.6molSO2 b. 2SO2 + O2 -> 2SO3, 96.0% yield .960(30.6molSO2 x 2molSO3/2molSO3) = 29.3molSO3 c. SO3 + H2SO4 -> H2S2O7, 100.% yield 1.00(29.3molSO3 x 1molH2S2O7/1molSO3) = 29.3molH2S2O7 d. H2S2O7 + H2O -> 2H2SO4, 97.0% yield .970(29.3molH2S2O7 x 2molH2SO4/1molH2S2O7 x 98.09gH2SO4/1molH2SO4 x 1kg/103g) = 5.85kgH2SO4 6.
