Chemistry 107 LabComplex Ions of Cobalt (corrected)

Cobalt Lab: Synthetic schemes v2004Page 1 Chemistry 107 Lab Complex Ions of Cobalt http://academics.smcvt.edu/chemistry/CHEM_107/107_lab_stuff/Cobalt/cobalt_lab.htm CH 107 Cobalt lab 03/28/11 Page 2 of 8 INTRODUCTION -. Clearly draw the octahedral geometry) • Prepare a Table of Reagents as shown in: http://academics. A ligand can be displaced by another ligand.doc 2 . involve oxidation of cobaltous [Co2+ or Co(II)] ion in the presence of an appropriate ligand.8 mole/L. In the process. Don’t worry about ancillary reagents (water. That is the prelab.1 in your text.edu/chemistry/CHEM_107/107_lab_stuff/Cobalt/SA MPLE%20FORMAT%20FOR%20PRELAB%20COBALT%20LAB. • List the MW of CoCl2 • 6H2O and ammonium chloride. • Write the balanced equation for the reaction between ammonia and HCl. PROCEDURE Part 1: Preparation of hexaamminecobalt(III) chloride BEFORE YOU COME TO LAB: • READ SECTION 19. Plan to do the first part of Part I and the first part of Part II simultaneously on DAY 1. How many liters is this at STP? • Determine the MW of [Co(NH3)6]Cl3. and you will make three of them.is a spectator ion). • Concentrated ammonia is 14. • Look up the definition of “LIGAND”.1 in your text. (Hint: Cl. Calculate the number of moles of each reagent used in reaction I (except O2!). have been prepared. like those in this assignment. O2 gets reduced to what? • Define “REDUCTION”. • Co (II) gets oxidized to Co(III). • Draw the structure of [Co(NH3)6]Cl3 (see p 694. Typical preparative sequences.A large number of cobalt complexes. preparative procedures are given for trans-dichloro-bis-(ethylenediamine)cobalt(III) chloride. 695 in text. • Look up the definition of “OXIDATION”. In Parts 1 and 2. In Part 3. hexaamminecobalt(III) chloride and pentaamminechlorocobalt(III) chloride are prepared. HCl) or catalysts ( C ).smcvt. Before you come to lab: READ section 19. • Calculate how many moles of O2 you’ll need to bubble through to react with all your CoCl2 • 6H2O. Ethyl alcohol is volatile. Wash with 3 mL of cold ethyl alcohol. You can stop here Cool your solution in ice water and add more HCl if necessary. Label and save the product for analysis by the methods described in the Handout: Analysis http://academics. CoCl2 • 6H2O. Add 2mL of concentrated HCl to the filtrate. Add 6mL of concentrated ammonia and half a spatula of activated charcoal ( C.edu/chemistry/CHEM_107/107_lab_stuff/Cobalt/Analysis%20of%20Co %20Complexes%20%20by%20AA.smcvt. yields in excess of 65% have been obtained. During the bubbling. the color of the solution will change from reddish to yellowish brown. The carbon acts as a catalyst.40 g of ammonium chloride with 1 mL of water until most of the salts are dissolved. 3 .0 g of cobaltous chloride hexahydrate.doc You can stop here Part 2: Preparation of pentaamminechlorocobalt(III) chloride • • BEFORE YOU COME TO LAB: READ SECTION 19. as the result of the oxidation of Co(II) to Co(III) by oxygen.CH 107 Cobalt lab 03/28/11 Page 3 of 8 The reaction: I. until the next laboratory period.crystals should form. Bubble air through the solution for at least 90 minutes using an aspirator. In the recent past. so the crystals will dry quickly. The HCl reduces the solubility of the chloride salt by the common ion effect (Good old LeChatelier’s Principle!). mix 2. Transfer the filtrate to a beaker and leave it in your drawer. List the MW of Co(NO3)2 • 6H2O and ammonium carbonate. Then weigh the dried product. uncovered. Filter the mixture and wash with a few mLs of hot water to remove carbon. and 1.1 in your text. fresh from the package). and calculate the theoretical yield and percentage yield that you obtained. Filter the yellow crystals. 2CoCl2。6H2O + 2NH4Cl + 10NH3 + H2O2  2[Co(NH3)6]Cl3。2H2O +10H2O In a 150 mm test tube. Place the filter paper with your product in a 250 mL beaker and leave it in your drawer to dry until the next laboratory period.%20titration%20grav%20chloride%20&%20UV-Vis. doc • • Place 4. Don’t worry about ancillary reagents (water. and then filter the purple red crystals of tetraamminecarbonatocobalt(III) nitrate. Bubble air through the combined solution for three hours: II. Co(NO3)2 • 6H2O. HCl) or catalysts ( C ). takes several steps. write the net equation for the conversion of cobalt(II) nitrate to [Co(NH3)5Cl]Cl2. How many liters is this at STP? Notice that the road to [Co(NH3)5Cl]Cl2. Draw the structure of and List the MW of [Co(NH3)5Cl]Cl2. Pour the solution into an evaporating dish. [Co(NH3)4CO3]NO3 • ½H2O. In the following procedure. Calculate how many moles of O2 you’ll need to bubble through to react with all your Co(NO3)2 • 6H2O. Calculate the number of moles of each reagent used in reaction II (except O2!).smcvt.edu/chemistry/CHEM_107/107_lab_stuff/Cobalt/SA MPLE%20FORMAT%20FOR%20PRELAB%20COBALT%20LAB.8 mole/L. Evaporate the solution to 10 mL by heating the dish on a beaker of boiling water. Then add concentrated ammonia to bring the total volume up to the 35 mL mark and mix. Periodically add a total of 1.CH 107 Cobalt lab 03/28/11 Page 4 of 8 • • • Concentrated ammonia is 14. in 5 mL of water. Cool the dish well (15 to 30 minutes) in ice water.2 g of powdered ammonium carbonate in small portions. dissolve 2. (See page 695 in your text) Prepare a Table of Reagents as shown in: http://academics. You can stop here Get your LABELLED & STOPPERED SOLUTION OUT. By adding up equations II through VI. Now add the first solution to the second solution and mix. In a 200 mm test tube. the ultimate product.0 g of cobaltous nitrate hexahydrate. Co(NO3)2 + (NH4)2CO3 + 3 NH3 + 1/4 O2  [Co(NH3)4CO3](NO3).0 g of ammonium carbonate in a 50 mL or 100 mL graduate cylinder and add water to fill to the 25 mL mark and stir to dissolve the solid. The reaction solution may be LABELLED & stoppered until the next laboratory period.½ H2O + NH4NO3 (muddy blue-ish purple) (burgundy red/purple) The color of the solution will change from muddy blue-ish purple (cobaltous) to burgundy red/purple (cobaltic). use all of the product you have just 4 . Let the solution cool to cause crystallization. Filter the violet crystals. Co(NO3)2 + (NH4)2CO3 + 4NH3 + 1/4O2 + 3HCl  [Co(NH3)5Cl]Cl2 + NH4NO3 + 1. Dissolve the tetraamminecarbonatocobalt(III) nitrate in 8-10 mL of water in a large test tube. III. [Co (NH3)4 CO3 ](NO3) + 3H+ + 2H2O  H2CO3 + [Co(NH3)4(H2O)2]3+ + HNO3 IV. H2CO3  H2O + CO2 ( g ) About 1 mL should be enough for the complete reaction Neutralize the solution with concentrated ammonia (check with red litmus) and add 1 mL excess. Heat the test tube containing the solution in a beaker of boiling water for 20 minutes. [Co(NH3)4(H2O)2]3+ + NH3  [Co(NH3)5H2O]3+ + H2O Cool the mixture. Add concentrated hydrochloric acid until all the carbon dioxide is expelled (bubbles stop). The following reaction occurs: VI. which is pentaamminechlorocobalt(III) chloride (the modern name). Label and save the product for analysis by the methods described in the Handout: Analysis You can stop here 5 . [Co(NH3)5Cl]Cl2. then add 10 mL of concentrated hydrochloric acid.5H2O + CO2 + HNO3 Cool the test tube in ice water. The reaction is: V.CH 107 Cobalt lab 03/28/11 Page 5 of 8 obtained. Heat the test tube in the water bath for another half hour. and weigh the dry product. Dry as in Part 1. Calculate the theoretical yield and the percentage yield. [Co(NH3)5H2O]3+ + 3Cl. and then with alcohol. wash them with a few drops of ice water.+ H+  [Co(NH3)5Cl]Cl2 + H3O+ NET RX: (Adding up II – VI) VII. add distilled water from time to time to keep the volume of solution between 3 and 5 mL. After one hour of aeration. Try not to get the ethylenediamine solution on your skin or clothing because it is toxic. and since ethylenediamine is not very volatile. Draw the structure of and List the MW of [Co(en)2Cl2]Cl• HCl (See p 698 in your text) Prepare a Table of Reagents as shown in: http://academics. Clamp the assembly in a beaker of water on a ring stand so that it can be heated during the aeration. Bring the water to boiling. remove the test tube from the water bath. This 6 . wash the area well with water immediately. It is 10% mass/mass ethylene diamine in water.5 g of cobaltous chloride hexahydrate (CoCl2 • 6H2O) in 10 mL of distilled water in a 200 mm test tube. Calculate the MOLARITY of the 10% ethylene diamine. If the dark red solution does not turn green as the hydrochloric acid is added. Fit the test tube with glass tubing and a stopper for bubbling air through the solution. and draw air through the test tube with an aspirator for one hour.edu/chemistry/CHEM_107/107_lab_stuff/Cobalt/SA MPLE%20FORMAT%20FOR%20PRELAB%20COBALT%20LAB. The dark green crystals are the hydrogen chloride salt of trans-dichloro-bis-(ethylenediamine)cobalt(III) chloride.CH 107 Cobalt lab 03/28/11 Page 6 of 8 Part 3: trans-Dichloro-bis-(ethylenediamine)cobalt(III) chloride BEFORE YOU COME TO LAB: READ SECTION 19. Concentrated HCl is 12 M.00 g/mL. the ethylenediamine will not be lost during aeration. If you do get some on you.doc • • • • • • Dissolve 1. Ammonia. List the MW of CoCl2 • 6H2O Calculate the number of moles you will use in this experiment. Because evaporation of the reaction solution will occur during aeration. The density is 1. Determine the MW of ethylene diamine (H2N-CH2-CH2-NH2). Cool the test tube in ice water. concentrate the solution in an evaporating dish on a beaker of boiling water (as in Part 2).1 in your text. The oxidation proceeds faster at the higher temperature. add 5 mL of a 10% ethylenediamine solution and mix well. The dark red solution should turn dark green. and immediately add 5mL of concentrated hydrochloric acid. To the solution. and add 1 mL of concentrated hydrochloric acid before cooling. as in Parts 1 and 2.smcvt. would be lost readily. Calculate how many Moles of ethylene diamine you will use in this experiment. Calculate how many moles of HCl you will use in today’s experiment. emerald-green crystals may be obtained. [Co(en)2Cl2]Cl • HCl + heat  [Co(en)2Cl2]Cl + HCl(g) Filter the crystals. This can be tested by holding a piece of moistened blue litmus paper over the mouth of the test tube. crush the crystals. Calculate the theoretical yield and the percentage yield. beautiful large diamond-shaped. ANALYZE THEM ACCORDING TO THE PROTOCOLS IN THE ANALYSIS HANDOUT. Weigh the dried product. Label and save the product for analysis by the methods described in the Handout: Analysis You can stop here NOW THAT YOU HAVE MADE THREE COBALT COMPLEXES. and stir to form a slurry. Another crop will probably result. it may be advisable to concentrate the solution from which the crystals were obtained. 7 . No more hydrogen chloride should be given off. VIII.5 g of cobaltous chloride and calculated number of moles of ethylenediamine (remember there are two ethylenediamine ligands in each molecule of [Co(en)2Cl2]Cl. Place the green plates of trans-[Co(en)2Cl2]Cl • HCl in a DRY 150 mm test tube with 5 mL of anhydrous methyl alcohol.CH 107 Cobalt lab 03/28/11 Page 7 of 8 can be placed in your drawer uncovered until next week for crystal formation. and calculate the maximum yield theoretically possible from 1. If the yield is small (less than half a gram). 2 CoCl2(aq) + 4 H2N-CH2-CH2-NH2 + 4 HCl + ½ O2  2 [Co(en)2Cl2]Cl • HCl + H2O IX. If the mixture is left in your drawer for several days. Heat the test tube for 15 minutes in boiling water. van Houten. Nicholas James and Dr. CITING SOURCES OTHER THAN ONES YOU YOURSELF HAVE ACTUALLY USED WILL RESULT IN 500 LAB POINTS DEDUCTED. Foust and P. Paul Frail. J.C. Olgiati from the original handout by Dr. READ THEM AND USED THEM. Rev. Some material was adapted from an article in the Journal of Chemical Education by R. ARE WE CLEAR? 8 . See also Coord. Sarah Locknar. Chem. 12: 151 (1974)]. K.D. COORD CHEM REV or ANY OTHE SOURCE IN YOUR PAPER UNLESS YOU YOURSELF HAVE OBTAINED THEM THROUGH INTERLIBRARY LOAN. We gratefully acknowlege the assistance of Melissa Gaudette. DO NOT REFERENCE THE JCE.CH 107 Cobalt lab 03/28/11 Page 8 of 8 -Adapted by Dr. Ford [JCE 47:165 (1970).