UW Department of Chemistry Lab Lectures Online

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1 Lab 6: Spectrochemical Series Procedure Overview Part A Weigh out copper(ii) sulfate pentahydrate and transfer to a beaker. Record the mass of the solid. Add 1 M HCl and stir to dissolve the solid. Add glycine to the beaker containing the copper sulfate solution. Record the mass of glycine. Warm the solution for an hour in a warm water bath. Move on to Parts B-E while the solution is warming. After an hour, add sodium bicarbonate to neutralize the HCl in the copper sulfate solution; the Cu(gly) 2 H 2 O will precipitate. Vacuum filter the precipitate and dry it under a heat lamp. Transfer the mostly dried precipitate to a tared beaker and record the mass of Cu(gly) 2 H 2 O produced. Add DI H 2 O to dissolve the solid, heating gently in the warm water bath, if necessary. Gravity filter the solution, preserving the liquid filtrate for measurement of λ max in Part C. Part B Prepare the Cu(H 2 O) 2+ complex from the 0.10 M copper(ii) sulfate stock solution and additional DI H 2 O. Measure the λ max and record the value in your notebook. Prepare the CuCl 4 2- (chloro) complex from the 0.10 M copper(ii) sulfate stock solution, additional DI H 2 O, and solid NaCl. Transfer part of the solution to a cuvette, measure the λ max, and record the value in your notebook. Prepare the Cu(NH 3 ) 4 2+ complex from the chloro complex reserved from the previous step and concentrated NH 4 OH. (Do this in the hood!) Transfer part of the solution to a cuvette, measure the λ max, and record the value in your notebook. Part C In a test tube, combine copper(ii) sulfate stock solution and a small amount of ethylenediamine. Cover the test tube and swirl gently to mix. Add a small amount of water, re-cover, and swirl to mix. Transfer part of the solution to a cuvette, measure the λ max, and record the value in your notebook. In a test tube, combine copper(ii) sulfate stock solution and a small amount of dimethylgloxime. Cover the test tube and swirl gently to mix. Add a small amount of water, re-cover, and swirl to mix. Transfer part of the solution to a cuvette, measure the λ max, and record the value in your notebook. 1 of 7

2 In a test tube, combine copper(ii) sulfate stock solution and a small amount of saturated potassium oxalate. Cover the test tube and swirl gently to mix. Add a small amount of water, if necessary, re-cover, and swirl to mix. Transfer part of the solution to a cuvette, measure the λ max, and record the value in your notebook. Obtain a small amount of copper acetylacetonate solution from the dispenser in the hood. Transfer part of the solution to a cuvette, measure the λ max, and record the value in your notebook. Transfer part of the Cu(gly) 2 H 2 O filtrate solution from Part A to a cuvette, measure the λ max, and record the value in your notebook Part D Obtain a small amount of ferroin solution from the dispenser in the hood. Measure the λ max and record the value in your notebook. Obtain a small amount of iron acetylacetonate solution from the dispenser in the hood. Measure the λ max and record the value in your notebook. Obtain a small amount of potassium ferricyanide solution from the dispenser in the hood. Measure the max and record the value in your notebook. Part E Obtain a small amount of hexachlorocobalt(iii) solution from the dispenser in the hood. Measure the λ max and record the value in your notebook. Obtain a small amount of hexaamminecoblat(iii) solution from the dispenser in the hood. Measure the λ max and record the value in your notebook. Record the readings from the magnetic susceptibility balance for each of the samples. Materials To be checked out from the stockroom: None From your lab drawer: (8) Cuvettes with caps (4) 100-mL beakers 10-mL graduated cylinder 100-mL graduated cylinder 125-mL filter flask Crystallizing dish 43 mm Buchner funnel Spatula Glass stirring rod with rubber policeman Long stem glass funnel (6) 25x150 mm test tubes Grease pencil 2 of 7

3 Provided in the lab: Ocean Optics diode array spectrophotometer interfaced with a computer Copper(II) sulfate pentahydrate, CuSO O Glycine, NH 2 CH 2 COOH 1 M HCl Sodium bicarbonate, NaHCO M Copper(II) sulfate solution Sodium chloride, NaCl Concentrated ammonium hydroxide, NH 4 OH 0.20 M ethylenediamine (en) 1% dimethylgloxime (dmg) in ethanol Saturated potassium oxalate (K 2 C 2 O 4 ) (aq) solution Copper acetylacetonate solution, Cu(acac) 2 (in ethanol) Ferroin solution, Fe(phen) 3 2+ (aq) Iron acetylacetonate solution, Fe(acac) 3 (in ethanol) Potassium ferricyanide solution, K 3 Fe(CN) 6 (aq) Hexacholorcobalt(III) solution, CoCl 6 - (in conc. HCl) Hexaamminecobalt(III) solution, Co(NH 3 ) 6 3+ (aq) Magnetic Susceptibility Balance Hexacholorcobalt(III), CoCl 6 - (in magnetic susceptibility tube) Hexaamminecobalt(III), Co(NH 3 ) 6 3+ (in magnetic susceptibility tube) Parafilm squares Filter paper (20-m) Filter paper (70-mm) Kimwipes Disposable plastic graduated 1-mL pipets Hot plates Clay pipe triangle Iron ring Heat lamps PROCEDURE Important remark: Proceed with speed in order to accomplish all the tasks required. RECORD ALL DATA IN YOUR NOTEBOOK. THEN NEATLY TRANSFER THE NECESSARY DATA VALUES AND CALCULATIONS TO THE REPORT SHEET THAT IS DUE BY THE END OF THE LAB PERIOD. Be sure you record observations of color and appearance of solids and solutions during the reactions. After starting with Part A., Parts B., C., D., and E. can be done in any order. All of the peaks you will be observing should appear between 350 and 900 nm. 3 of 7

4 A. Preparation of cis-bis (glycinato) copper(ii) monohydrate, Cu(gly) 2. H2 O 1. Place 0.5 g of copper(ii) sulfate pentahydrate, CuSO 4. 5H2 O, in a 100-mL beaker and add 3 ml of 1 M HCl. Record the CuSO 4. 5H2 O mass in your lab notebook. The acid keeps the product complex in solution until you precipitate it in step When the complex has dissolved, add 0.25 g of glycine, NH 2 CH 2 CO 2 H, to the solution. Record the glycine mass in your lab notebook. 3. Prepare a water bath by placing a clay pipe triangle in the crystallizing dish and filling the dish half full with tap water. This assembly is placed on a hot plate and the beaker containing the solution is placed in the water so that it rests on the clay pipe triangle. 4. Warm the solution for one hour on the hot plate (without boiling the water in the water bath). During this hour, proceed to Part B (preparation and spectra of the unidentate complexes). 5. Add sodium bicarbonate, NaHCO 3, in small portions (avoid a large excess) until precipitation is complete and CO 2 evolution stops. Do not add water or rinse the precipitate with water, as it will substantially decrease your yield. Vacuum filter the precipitate with a Buchner funnel, then let the sample dry under a heat lamp. While the sample is drying, continue with Parts B-E. 6. Place a 100 ml beaker on the electronic balance. Press "tare" so that the balance reads zero. Using a stirring rod with a policeman rubber, transfer the Cu(gly) 2.H 2 O from step 5 into the beaker. Record the mass of the Cu(gly) 2.H 2 O. 7. Add 20 ml of deionized water to the beaker and place it in a hot (not boiling) water bath. Warm the solution, swirling the beaker frequently until the solid is dissolved. 8. When the Cu(gly) 2.H 2 O solid has dissolved, some solid impurities may remain. Support the conical glass funnel with an iron ring and position it over a 100-mL beaker. Select a filter paper of appropriate size; fold it in quarters and open the fold to form a paper cone filter. Place it in the funnel (it should come up about two-thirds of the glass wall) and moisten with a little deionized water to seat it properly. Then carefully pour the hot solution through this gravity filter. Preserve the liquid filtrate. This solution will be used for the spectrum measurement. 9. Used filter paper should be placed in the solid waste container in the hood. Instrument instructions for Parts B through E In Parts B through E, you will make measurements of the λ max for a series of solutions using one of the spectrophotometer/computer stations that have been set up in the lab. The spectrophotometers have already been calibrated, the wavelength ranges set, and are in Absorbance mode. Place your sample cuvette in the cuvette holder, making sure the clear sides are oriented in the path of the light beam. To determine a λ max measurement, click on the center of the peak using the left mouse button. The wavelength, channel number, and 4 of 7

5 absorbance value will be shown in the legend at the bottom left of the screen (you only need to record the λ max for the purposes of this experiment). You can fine-tune the selected wavelength by using the cursor keys on the computer keyboard. If the absorbance of your sample is very high (>3.0), the signal will become saturated and the displayed absorbance will drop to zero on the screen (it will appear as a peak with the middle cut out of it). If this is the case, you will have to dilute your sample and record another absorbance measurement. Notify your TA if there is a problem with the instrument. B. Preparation and Measurement of λ max of Unidentate Cu(II) ligands 1. Cu(H 2 O) 4 2+, aquo (water) complex Obtain 10 ml of the stock 0.10M copper sulfate solution. Using a disposable plastic pipet, add 1 ml to a cuvette. Add 2 ml of DI water to dilute the sample. Record λ max. If more than one peak appears, record the λ max associated with the absorption of the highest wavelength. If the sample has an absorbance higher than 2, dilute the sample by taking a small volume (< 1mL) of the copper sulfate in the cuvette and adding water to dilute. Do not dilute your stock solution, but rather the small portion of it that is in the cuvette. Aim for an absorbance between 0.10 and CuCl 4 2-, chloro (Cl - ) complex Using a graduated cylinder, add 5 ml of 0.10 M copper sulfate stock solution to a beaker. Add ml of deionized water and 2 g of solid NaCl. Stir the mixture with a glass stirring rod to dissolve the NaCl. Using a disposable plastic pipet, add 2-3 ml to a cuvette. Record λ max. If more than one peak appears, record the λ max associated with the absorption of the highest wavelength. If the sample has an absorbance higher than 2, dilute the sample by taking a small volume in the cuvette and adding water to dilute. 3. Cu(NH 3 ) 4 2+, ammine complex Using a graduated cylinder, add 5 ml of the chloro complex solution to a new clean test tube. Add 1 ml concentrated NH 4 OH (do this in the hood!). Initially, light blue copper hydroxide precipitates. This should re-dissolve upon stirring. If necessary, add more NH 4 OH. Transfer the solution to a cuvette and record λ max. If more than one peak appears, record the λ max associated with the absorption of the highest wavelength. 4. All waste solutions for this part should be placed in the 4-L amber waste bottles in the hood. C. Preparation and Measurement of λ max of Bi-dentate Cu(II) ligands 1. Cu(en) 2 2+ complex Place 1 ml of 0.10 M copper(ii) sulfate stock solution into a clean test tube. Add 1 ml of the 0.20 M ethylenediamine to the test tube. Cover with Parafilm and swirl to mix. Add 5 ml of DI water. Cover with Parafilm and swirl to mix. Transfer the solution to a cuvette and record λ max. If more than one peak appears, record the λ max associated with the absorption of the highest wavelength. 5 of 7

6 2. Cu(dmg) 2 complex Repeat step 1, but this time add 1 ml of 1% dmg solution to the copper sulfate solution instead of ethylenediamine. 3. Cu(ox) 2 2- complex Repeat step 1, but this time add 1 ml saturated potassium oxalate solution instead of ethylenediamine. Cover with Parafilm and swirl to mix. If a precipitate appears add DI water in 5-mL increments and after each addition, cover with Parafilm and swirl to mix. Keep adding water until all the precipitate is dissolved. Transfer the solution to a cuvette and record λ max. If more than one peak appears, record the λ max associated with the absorption of the highest wavelength. 4. Cu(acac) 2 complex A solution of Cu(acac) 2 is available in the hood. Obtain 2-3 ml of this sample into a clean, dry cuvette and record its λ max. 5. Cu(gly) 2. H2 O complex Record the λ max for the Cu(gly) 2. H2 O filtrate solution that you made in Part A. 6. All waste solutions for this part should be placed in the 4-L amber waste bottles in the hood. D. Measurement of λ max of Octahedral Iron(II,III) Complexes 1. Obtain 2-3 ml of ferroin, Fe(phen) 3 2+ (aq), in a clean, dry cuvette. Record λ max. 2. Obtain 2-3 ml of Fe(acac) 3 (aq) in a clean, dry cuvette. Record λ max. 3. Obtain 2-3 ml of K 3 Fe(CN) 6 (aq) in a clean, dry cuvette. Record λ max. 4. Fe(phen) 3 2+, Fe(acac) 3, and K 3 Fe(CN) 6 solutions should be placed in the 4-L amber waste bottles in the hood. E. Spectral and Magnetic Properties of CoCl 6 3- and Co(NH 3 ) Obtain 2-3 ml of CoCl 6 3- (in conc. HCl) in a clean, dry cuvette. Record λ max. 2. Obtain 2-3 ml of Co(NH 3 ) 6 3+ in a clean, dry cuvette and record its λ max. 3. From the magnetic susceptibility balance, record R for CoCl 6 3- and Co(NH 3 ) 6 3+ which are both solids. The samples will already be inserted in calibrated balances, so you just need to record the R value shown on the display. 4. Co(NH 3 ) 6 3+ and CoCl 6 3- solutions should be placed in the 4-L amber waste bottles in the hood. 6 of 7

7 Before You Leave the Lab 1. Upon completing the experiment, show your work to your TA. 2. Obtain your TA s signature in your lab notebook and turn in the carbon copy of your lab notebook pages associated with this experiment. 3. Clean your lab bench and have your TA check your equipment drawer and lab bench. Waste Disposal All solutions should be placed in the 4-L amber waste bottles in the hood. Filter paper should be placed in the trash. Information to Enter in your Notebook during the Lab Part A Masses of copper(ii) sulfate pentahydrate and glycine added to the beaker. Volumes and identities of liquids added. Mass of precipitate recovered after vacuum filtration and drying. Observations as the sample is prepared (precipitates forming/dissolving). Parts B-D Part E Observations as solutions are prepared (precipitates forming/dissolving). Volumes and identities of liquids used. λ max for all 11 solutions prepared/provided. Volumes and identities of liquids used. λ max for each of the 2 solutions provided. R value from magnetic susceptibility balance for both solid samples Any other notes or observations that will help when you work on your post-lab report or need to explain your results 7 of 7