Class Note for CHEM 242 at UMass(5)
Class Note for CHEM 242 at UMass(5)
Popular in Course
Popular in Department
This 8 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Massachusetts taught by a professor in Fall. Since its upload, it has received 23 views.
Reviews for Class Note for CHEM 242 at UMass(5)
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 02/06/15
Experiment 1 HardSoft Acids and Bases Altering the CquCu2 Equilibrium with Nitrogen Oxygen or Halide Ligands Pre Lab Assignments and Notes 1 Calculate the correct mass of stalen needed MW 2683 gmol see molecular structure on page 3 to form a 11 complex with CuClz using 2 mL of a 003 M copperll chloride solution 2 Write out the procedure you will use in Part G to determine the relative stabilities of CuII and Cul when ligated by salen State what you expect to observe when you carry out the procedure You need not calculate the quantities of the reagents you ll use Note The abbreviation quotenquot refers to ethylenediamine a ligand with two nitrogen donor sites bridged by an ethane moiety HzNCHZCHzNHZ Both nitrogens bind to metals as shown H2N M IH2 H2N NH2 ethylenediamine Experimental Procedure SAFE T Y N 0T ES Aqueous ammonia ammonium hydroxide gives off corrosive vapors Handle this reagent in the hood Ethylenediamine may give off irritating vapors handle in hood H Cl aqueous ammonia and 30 H 2 02 are extremely corrosive H 202 can react violently with organic solvents and substances such as clothes hair paper and dust Wipe up all spills immediately with water If skin or eyes are exposed instantly ush the affected area with copious amounts of water for fifteen minutes H zsalen is a skin irritant if exposed wash thoroughly with water Complexation of CopperII by Nitrogen Donors A Add about lmL of 003M copperII chloride solution a small test tube and in the hood add 1 mL of 6 M aqueous ammonia Record your observations Color Color change Precipitation Gas evolution Other changes Or no changes thoroughly and completely B Add about lmL of 003M copperII chloride solution to a small test tubes and in the hood add 1 mL of 25 aqueous ethylenediamine to the other As always in this week39s experiment record observations Reduction of CopperII to CopperI by Halide Ligands C Four 10 mL of 003M copperII chloride solution into a small Erlenmeyer ask Add 1 g of ammonium chloride to the solution and stir or swirl to dissolve Note any changes Then heat the solution to boiling on a Bunsen burner to expel oxygen and add an excess of clean copper wire 3 of heavy gauge wire is more than enough or about 01 g of clean copper tumings and continue heating Note what happens as this slow heterogeneous reaction proceeds and record the results Note39 CuH exhibits colors in the visible spectrum CuI does not exhibit visible colors and Cu0 is a red metal D Take a small test tube and add 2 mL of 003 M copperII chloride solution Add an equal amount of 01 M potassium iodide solution Note what happens and record the results as always record observations thoroughly and completely Oxidation of CopperI to CopperII By Amine Ligands E Divide the material both solution and precipitate in the test tube from procedure step D into two equal parts It should be a suspension of CuI In the hood add about 1 mL of 6 M aqueous ammonia to one part and carefully record your observations This reaction may proceed differently than reaction A Note any differences or similarities and explain them in the discussion section of your lab report F In the hood add about 1 mL of 25 ethylenediamine to the other part saved from D Again carefully record your observations G Synthesize the ligand bissalicylideneethylenediamine or salen or quotstalenquotsee Figure l by taking 3 mL of 95 ethanol in a test tube that also has a small magnetic stirring bar Heat the ethanol to boiling in an oil bath DO NOT use a Bunsen burner while stirring on a magnetic stirrerhotplate Immediately with continued heating and stirring add 030 mL 28 mmol of salicylaldehyde and then 010 mL 14 mmol of ethylenediamine 98 Heat and stir the solution to boiling about three minutes and then cool in an icewater bath to precipitate the yellow stalen Filter your product wash it with drops of icecold ethanol and dry it as much as possible on the filter by vacuum Then collect the crystals and spread them on a large piece of filter paper not the waxy paper used to weigh out reagents to airdry Weigh your product and determine and record your per cent yield 7 N N 0 7 H2N NH2 2 dOH gt OH HO 2H2O 5 sal HZSalen Cu2 CM N N ou O O Cusalen Figure 1 Synthesis of stalen and formation of the Cusalen complex Develop an experimental scheme to test the equilibria of the oxidation states of copper when ligated by the hard donor ligand salen For example 1 you could show that CuIIsalen is not easily reduced to copperI by copper metal Equation 1 below and thus that CuII is the more stable oxidation state when ligated by salen Alternatively 2 CuIsalen should spontaneously disproportionate to Cu0 and CuII Equation 2 demonstrating that the equilibrium lies towards CuIICu0 the more stable oxidation states with this harddonor ligand CuHsalen0 Cu0 2 CuIsalen39 1 2 CuIsalen S CuHsalen0 Cu0 salenz39 2 Show your scheme to a TA for approval before attempting your procedure Carry out your scheme and record your results Table 1 Reduction Potentials Involving Copper and Copper Compounds Couple EO value 1 Cu2 1 e CuI 086V 2 Cu2 C139 e CuCl 054v 3 12 2e39 3 2139 054v 4 011 aq e39 r Cus 052v 5 Cu2aq 2e39 3 Cus 037v 6 CuCl e39 3 Cu C1quot 014v 7 CuNH342 2e39 3 Cu 4NH3 0 12v 8 Cu2aq e Cu aq 0 15v 9 Cu1 e39 3 Cu 1 0 19v 10 Cuenzz 2e39 3 Cu 2en 050V en ethylenediamine Data Analysis 1 6 points Write the equation for each reaction you did in procedures A through G both charge and mass balance should be satis ed Then identify from the observations recorded in your notebook the products you obtained from each reaction and whether they concur with the expected products A and B are ligandcomplexing reactions Expected chemical products are A CuNH342 and B Cuenz2 C and D are reduction reactions so halfreactions must added be arrive at the balanced equations Table 1 above Halfreactions 2 and 6 are relevant to procedure C and l and 3 are relevant to procedure D Expected chemical products are C CuCl and D CuI E and F are oxidation reactions Halfreactions 7 and 9 are relevant to procedure E and 9 and 10 to procedure F Expected chemical products are E CuNH342 and F Cuenz2 2 4 points Using Table 1 write out individual halfreactions their balanced overall redox reactions and the overall E0 potential that describe the chemical reactions in procedures A through F Halfreactions 5 and 7 are relevant to procedure A Halfreactions 5 and 10 are relevant to procedure B Use your answers to Data Analysis topic 1 above for halfreactions and balanced equations relevant to procedures C F In each case the halfreactions should sum to the net balanced redox equation with no e39 left over 3 5 points Using Table I calculate the E0 for the preparation of CuI from CuII and Cu0 in the presence of chloride ion halfreactions 2 and 6 use your answers to procedure C from the above topics Calculate the E0 for the same reaction in the absence of chloride ion halfreactions 4 and 8 4 5 points Use the result from the previous problem to calculate the free energy change AGO for the preparation of CuI from copperII and Cu0 in the presence of chloride ion Then calculate the AG0 for the same reaction in the absence of chloride ion Discussion 1 6 points State what the HSAB theory predicts and discuss whether each of your obtained reaction products concurs with the HSAB predictions See the diagram depicting hard and soft acids and bases located at the end of this EP 2 5 points Discuss whether the E0 values obtained for procedures A through F correctly predict your reaction product results In any case did your results disagree with the predictions of the reactions overall E0 potential If so explain why that might be 3 6 points Discuss whether the E0 values for each of procedures A through F concur with what the HSAB theory predicts 4 4 points Discuss what the experimental scheme you developed in procedure G concerning the equilibria of the oxidation states of copper when ligated by salen proved in terms of the HSAB theory 5 6 points Compare the electrochemical potentials and the AG0 values for the preparation of CuI in the presence and absence of the chloride ion Which preparation is more thermodynamically favorable and why What is the reason for the difference in thermodynamic favorability of the two preparations 6 3 points In what ways do our experimental conditions vary from those used to calculate the standard E0 potentials Do the actual electrochemical potential values of our experimental conditions vary a great deal from the standard E0 potentials Use the identity of the products you obtained in procedures A through F to arrive at and justify your answer 10 points Conclusions What do your results the HSAB theory and calculated electrochemical potentials show about how we can manipulate the concentrations of different oxidation states of transition metals Questions 1 2 points Why is CuI colorless while CuII tends to be colored green or blue Think about electron configurations 2 3 points Copper 1 deactivators used in gasoline include a ligand analogous to salen with 12 diaminopropane in place of en This ligand prevents the copperI catalyzed formation of gum in the gasoline Explain why this works in terms of your results Hard 8 Soft Acids 8 Bases Table 81 from Wullsberg Principls a Dzscn39piive Inurxunic Chemistryquot u u an N M an lb ml 019 n m a 57 Lil mo no cm l 9 mu m u a II 4 Nb u 139 u LI r u HadAid Cr LGG 1157 N Lu 1 Mo lo mmulnhh Pk Malia a mm 101 land ll AI my 15 2 Mn mu may on 2 a usf39unn us u m 1 m n Pd A ca lam smu T l x m u munu no m m mun Isqrz u 1 266 u n m It n An H 39n n a m n nu m 254 10 mm Hy 1a 3110 ms Pin 5 Eu Gd To Dy Hu a TM Yb m I2 I22 us 14 us Np Pu Am Cm Bk C 5 Flu Md No me 2 u u I u 11 u u u Humid m nIm h puma s u unm nuun m luubu Man a quotduly5d a a run mwmu 4 a thank
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'