Electrochemistry Kenneth E. Schnobrich

Electrochemistry Every element and ion has the potential to lose electrons as well as gain them - we can make use of these differences in potential to lose and gain in the design of an ELECTROCHEMICAL CELL. DEFINING TERMS: OXIDATION - the loss of electrons by a species REDUCTION - the gain of electrons by a species OXIDIZING AGENT - the substance that undergoes Reduction REDUCING AGENT - the substance that undergoes Oxidation

Electrochemistry DEFINING TERMS (cont.): HALF-CELL - the container in which an oxidation or a reduction reaction occurs SALT BRIDGE - allows a connection between the two half-cells and helps to maintain charge balance in the cell ELECTRODE - a substance that serves as either the Oxidizing or Reducing agent VOLTMETER - a device that allows us to measure the voltage generated by a particular combination of half-cells

Electrochemistry Which way will the electrons flow??

CHART “J” Na Mg Al Zn Fe Sn Pb H2 Cu Just a Sample Greater Tendency to Lose electrons Better Reducing Agent List was taken from a version of the NYS Tables for Chemistry

VOLTAIC CELL

Zn0 + Cu+2 -> Cu0 + Zn+2 Ecell = +1.10v Zn0 -> Zn+2 + 2e- + 0.76v Cu+2 + 2e- -> Cu0 + 0.34v Zn0 + Cu+2 -> Cu0 + Zn+2 Ecell = +1.10v e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- Oxidation - + Reduction e- KNO3 e- Anode Cathode NO3- K+ Mass decrease Mass increase

Chemical Reaction (REDOX) ------> Energy SHORT-HAND NOTATION Zn0|Zn+2||Cu0|Cu+2 Chemical Reaction (REDOX) ------> Energy

Mg|Mg+2||Ni0|Ni+2 What do we know: Mg is the anode (- electrode) Ni is the cathode (+ electrode) Mg is oxidized Mg0 -> Mg+2 Ni+2 is reduced Ni+2 + 2e- -> Ni0 Mg electrode decreases in mass Ni electrode increases in mass K+ moves toward Ni cell / NO3- moves toward Mg cell

Ecell CALCULATION Mg0 -> Mg+2 + 2e- Ni+2 + 2e- -> Ni0 +2.37v Mg0 + Ni+2 -> Mg+2 Ni0 +2.11v

WHERE WILL A REDOX Rx OCCUR?? Using Table J WHERE WILL A REDOX Rx OCCUR?? Al0 Ag0 Cu0 Al0 Mg+2 Cu+2 Ag+1 Fe+2

ELECTROLYTIC CELL Energy ---> Chemical Reaction (REDOX)