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Electrochemical Cells

Electrochemical Cells. By, Marvin Lu and Riley Corr. 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. Mg metal.

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Electrochemical Cells

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  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.

  3. Mg metal Electrons are transferred from Mg to Cu2+, but there is no useful electric current. 2+ Cu ions CHEMICAL CHANGE --->ELECTRIC CURRENT Oxidation: Mg(s)---> Mg2+(aq)+2e- Reduction: Cu2+(aq)+2e- --->Cu(s) ----------------------------------------- Cu2+(aq)+Mg(s)--->Mg2+(aq)+Cu(s)

  4. l Cu Mg salt bridge 2+ 2+ Mg ions Cu ions CHEMICAL CHANGE --->ELECTRIC CURRENT voltmeter • 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.

  5. wire Cu Mg salt bridge 2+ 2+ Mg ions Cu ions Mg --> Mg2+ + 2e- Cu2+ + 2e- --> Cu Oxidation Anode Negative Reduction Cathode Positive •Electrons travel thru the voltmeter. • Salt bridge allows anions and cations to move between electrode compartments. <--Anions Cations-->

  6. Procedure • Obtain Goggles • Obtain a 3”x5” piece of copper sheet and a 3” long magnesium ribbon • Obtain .5M, .1M, and .01M Mg(NO3)2 solutions • Obtain .5M, .1M, and .01M Cu(NO3)2 solutions • Obtain a .1M CuSO4 solution • Obtain filter paper and .1M KNO3 solution for salt bridge. To make salt bridge, roll filter paper and soak in solution. • Obtain a voltmeter, set it to 40V. • Obtain two 50mL beakers, and two 50mL graduated cylinders.

  7. Procedure (Continued) • Set up electrochemical cells as follows: • - Measure out 30mL of each solution to be used, pour into • separate beakers. • - Make a salt bridge and place an end into each beaker. • - Place the copper into the solution containing the copper ion. • - Place the magnesium into the solution containing the • magnesium ion. • - Connect the voltmeter to the electrodes, the red wire should • attach to the Copper, the black to the Magnesium. • Repeat the procedure for all combinations of solutions below.

  8. Cu Mg 2+ 2+ Mg ions Cu ions Electrochemical Cell Voltmeter Salt Bridge KNO3 Anode Cathode

  9. Observations • 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 solution was clear. • Solutions were prepared from solid salts: Cu(NO3)2 •3H2O, Mg(NO3)2 •6H2O, KNO3 • The CuSO4 solution was prepared from a .4M solution of unknown quality. • BK Precision Voltmeter • Voltage readings required some time to stabilize.

  10. Data

  11. Discussion In this lab, Mg(NO3)2 and Cu(NO3)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 Cu2+ ions was changed from Cu(NO3)2 to CuSO4. Once again, there was a negligible change in voltage.

  12. Error • The CuSO4 solution was prepared from a .4M solution of unknown quality. • The Cu(NO3)2 solution was a hydrate but the exact chemical formula was unknown. It was assumed to be Cu(NO3)2 •3H2O based on the Flinn Scientific chemical and biological catalog reference manual 2001 • Not all of the impurities of the magnesium ribbon were removed.

  13. Bibliography 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_isbn_issn=003033604X&chapter_number=20&resource_id=21&altname=PowerPoints www.ivygreen.ctc.edu/knutsen/chem160/vltaicll.html

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