1. Electrochemical Cells By, Marvin Lu and Riley Corr

2. Purpose To determine the effects of changing the concentrations of solutions and the identities of the solutions themselves on the voltage in an electrochemical cell. To determine the effects of changing the concentrations of solutions and the identities of the solutions themselves on the voltage in an electrochemical cell.

3. Oxidation: Mg(s)---> Mg 2+ (aq)+2e- Reduction: Cu 2+ (aq)+2e- --->Cu(s) ----------------------------------------- Cu 2+ (aq)+Mg(s)--->Mg 2+ (aq)+Cu(s) Electrons are transferred from Mg to Cu 2+, but there is no useful electric current. CHEMICAL CHANGE ---> ELECTRIC CURRENT Mg metal Cu 2+ ions

4. CHEMICAL CHANGE ---> ELECTRIC CURRENT To obtain a useful current, we separated the oxidizing and reducing agents so that electron transfer occurred thru a volt meter. To obtain a useful current, we separated the oxidizing and reducing agents so that electron transfer occurred thru a volt meter. This is accomplished in a GALVANIC or VOLTAIC cell. A group of such cells is called a battery. Mg 2+ ions Cu 2+ ions salt bridge l voltmeter

5. Electrons travel thru the voltmeter. Electrons travel thru the voltmeter. Salt bridge allows anions and cations to move between electrode compartments. Salt bridge allows anions and cations to move between electrode compartments. Electrons travel thru the voltmeter. Electrons travel thru the voltmeter. Salt bridge allows anions and cations to move between electrode compartments. Salt bridge allows anions and cations to move between electrode compartments. Mg --> Mg2 + + 2e- Cu 2+ + 2e- --> Cu <--AnionsCations--> OxidationAnodeNegativeOxidationAnodeNegativeReductionCathodePositiveReductionCathodePositive Mg 2+ ions Cu 2+ ions wire salt bridge

6. Procedure Obtain Goggles Obtain Goggles Obtain a 3”x5” piece of copper sheet and a 3” long magnesium ribbon Obtain a 3”x5” piece of copper sheet and a 3” long magnesium ribbon Obtain.5M,.1M, and.01M Mg(NO 3 ) 2 solutions Obtain.5M,.1M, and.01M Mg(NO 3 ) 2 solutions Obtain.5M,.1M, and.01M Cu(NO 3 ) 2 solutions Obtain.5M,.1M, and.01M Cu(NO 3 ) 2 solutions Obtain a.1M CuSO 4 solution Obtain a.1M CuSO 4 solution Obtain filter paper and.1M KNO 3 solution for salt bridge. To make salt bridge, roll filter paper and soak in solution. Obtain filter paper and.1M KNO 3 solution for salt bridge. To make salt bridge, roll filter paper and soak in solution. Obtain a voltmeter, set it to 40V. Obtain a voltmeter, set it to 40V. Obtain two 50mL beakers, and two 50mL graduated cylinders. Obtain two 50mL beakers, and two 50mL graduated cylinders.

7. Trial:12345 [Mg(NO 3 ) 2 ] (mol/L).1.01.5.1.1 [Cu(NO 3 ) 2 ] (mol/L).1.1.1.01.5Trial:6 [Mg(NO 3 ) 2 ] (mol/L).1 [CuSO 4 ] (mol/L).1 Set up electrochemical cells as follows: Set up electrochemical cells as follows: - Measure out 30mL of each solution to be used, pour into - Measure out 30mL of each solution to be used, pour into separate beakers. separate beakers. - Make a salt bridge and place an end into each beaker. - Make a salt bridge and place an end into each beaker. - Place the copper into the solution containing the copper ion. - Place the copper into the solution containing the copper ion. - Place the magnesium into the solution containing the - Place the magnesium into the solution containing the magnesium ion. magnesium ion. - Connect the voltmeter to the electrodes, the red wire should attach to the Copper, the black to the Magnesium. attach to the Copper, the black to the Magnesium. Repeat the procedure for all combinations of solutions below. Repeat the procedure for all combinations of solutions below. Procedure (Continued)

8. Anode Cathode Electrochemical Cell Mg 2+ ions Cu 2+ ions Voltmeter Salt Bridge KNO 3

9. Observations Copper solutions had blue color, the higher the concentration, the darker the color. Copper solutions had blue color, the higher the concentration, the darker the color. Magnesium ribbon was coated in a white oxide, it was scraped off with a scoopula before use. Magnesium ribbon was coated in a white oxide, it was scraped off with a scoopula before use. Magnesium solution was clear. Magnesium solution was clear. Solutions were prepared from solid salts: Cu(NO 3 ) 2 3H 2 O, Mg(NO 3 ) 2 6H 2 O, KNO 3 Solutions were prepared from solid salts: Cu(NO 3 ) 2 3H 2 O, Mg(NO 3 ) 2 6H 2 O, KNO 3 The CuSO 4 solution was prepared from a.4M solution of unknown quality. The CuSO 4 solution was prepared from a.4M solution of unknown quality. BK Precision Voltmeter BK Precision Voltmeter Voltage readings required some time to stabilize. Voltage readings required some time to stabilize.

10. Data Trial:123456 Voltage (V) 1.471.761.551.661.671.54

11. Discussion In this lab, Mg(NO 3 ) 2 and Cu(NO 3 ) 2 were used as solutions in a voltaic cell. Concentrations of both were varied and the differences in voltage were negligible. In trial 6, the source of Cu 2+ ions was changed from Cu(NO 3 ) 2 to CuSO 4. Once again, there was a negligible change in voltage.

12. Trial:12345 [Mg(NO 3 ) 2 ] (mol/L).1.01.5.1.1 [Cu(NO 3 ) 2 ] (mol/L).1.1.1.01.5 Voltage (V) 1.471.761.551.661.67 Trial:6 [Mg(NO 3 ) 2 ] (mol/L).1 [CuSO 4 ] (mol/L).1 Voltage (V) 1.54

13. Error The CuSO 4 solution was prepared from a.4M solution of unknown quality. The CuSO 4 solution was prepared from a.4M solution of unknown quality. The Cu(NO 3 ) 2 solution was a hydrate but the exact chemical formula was unknown. It was assumed to be Cu(NO 3 ) 2 3H 2 O based on the Flinn Scientific chemical and biological catalog reference manual 2001 The Cu(NO 3 ) 2 solution was a hydrate but the exact chemical formula was unknown. It was assumed to be Cu(NO 3 ) 2 3H 2 O based on the Flinn Scientific chemical and biological catalog reference manual 2001 Not all of the impurities of the magnesium ribbon were removed. Not all of the impurities of the magnesium ribbon were removed.

14. Bibliography http://bkprecision.com/www/np_searchmodel7.asp?lf= Dual+Display+RS%2D232+Interface+Multimeters http://bkprecision.com/www/np_searchmodel7.asp?lf= Dual+Display+RS%2D232+Interface+Multimeters http://www.brookscole.com/cgi- Brookscole/course_products_bc.pl?fid=M63&product_isb n_issn=003033604X&chapter_number=20&resource_id =21&altname=PowerPoints http://www.brookscole.com/cgi- Brookscole/course_products_bc.pl?fid=M63&product_isb n_issn=003033604X&chapter_number=20&resource_id =21&altname=PowerPoints www.ivygreen.ctc.edu/knutsen/chem160/vltaicll.html www.ivygreen.ctc.edu/knutsen/chem160/vltaicll.html