Experiment 3 A Cycle of Copper Reactions Chemistry Department UCC1 st Year Practicals

Introduction Copper is one of the most important metals. Copper is reddish with a bright metallic lustre It is malleable, ductile, and a good conductor of heat and electricity (second only to silver in electrical conductivity) Its alloys, brass and bronze, are very important Has various oxidation states: 0 in elemental copper, +1, and +2 which is observable in corroded brass/bronze

Oxidation states Oxidation state is an indicator of the degree of oxidation of an atom The formal oxidation state is the theoretical charge the atom would have of all bonds were 100% ionic Oxidation is loss of electrons, reduction is gain of electrons (OIL RIG)

Oxidation States of Copper Transition metal – different oxidation states Cu 0 elemental state Cu +1 Cu +2 most common Cu +3 / Cu +4 unusual

Objectives To observe a sequence of chemical reactions starting and finishing in elemental copper metal, and to practice quantitative laboratory techniques. Cu  Cu(NO 3 ) 2  Cu(OH) 2  CuO  CuSO 4  Cu Cu(NO 3 ) 2 = copper nitrateCuSO 4 = copper sulfate Cu(OH) 2 = copper hydroxideCuO = copper oxide

Experiment 1(a) Cu + 4HNO 3  Cu(NO 3 ) 2 + 2NO 2  + 2H 2 O NO 2 given off as a coloured gas* Wash conical flask with 10 mL of water Transfer contents to beaker containing 100 mL of water *Carry out reaction in the fumehood

Experiment 1(b) Cu(NO 3 ) 2 + 2NaOH  Cu(OH) 2 + 2NaNO 3 Add 30 mL of NaOH solution to the solution of copper nitrate from part 1(a) while stirring with a glass rod A precipitate of insoluble copper hydroxide forms and settles to the bottom of the beaker Decant off the liquid, taking care not to lose any solid, wash with another 100 mL of water, heat gently, and decant once more Copper hydroxide precipitate

Experiment 1(c) Cu(OH) 2  CuO + H 2 O  Add 100 mL of water to the beaker containing the copper hydroxide and heat with a Bunsen burner  Maintain below boiling, and stir constantly to prevent bumping  Copper hydroxide is gradually dehydrated to copper oxide  Decomposition accompanied by a colour change

Experiment 1(d) Add 15 mL of 6.0 M sulfuric acid to the water/copper oxide mixture while stirring constantly Solution becomes blue in colour CuO + H 2 SO 4  Cu(SO) 4 + H 2 O

Experiment 1(e) Add 2 g of zinc metal to the blue copper sulphate solution Zinc oxidized while copper reduced Stir until solution becomes colourless Decant the liquid off, wash the remaining copper Isolate the metal, allow to dry and weigh CuSO 4 + Zn  ZnSO 4 + Cu

Calculation of % yield All reactions quantitative % yield = [actual yield/theoretical yield] x 100/1 Actual yield = weight of copper produced Theoretical yield = starting weight Yield of 100% is unlikely Leave wet copper product to dry in your locker until next week You can leave a blank space in your report for the % yield calculation and fill it in before you hand up your report

Title of experiment Date Introduction Experimental Procedure (Observations, including colour changes, precipitation evolution of gas etc.) Results – Calculation of % yield Discussion of results Answer questions in the manual Report

Be sure to take care handling any acids/bases during the experiment Make sure to record all your observations during each step Reports to be completed and handed to your demonstrator next practical session