Balance Redox Rxns: Fe(OH) 3 + [Cr(OH) 4 ] -1 Fe(OH) 2 + CrO 4 -2 in base
Electrochemistry
Metallic Conduction The flow of electrons through a metal
Ionic Conduction The movement of ions (electrolytes) through a solution Electrolytic Conduct.
Electrode The surface or point in which oxidation or reduction takes place
Anode The electrode where oxidation takes place An Ox (-)
Cathode The electrode where reduction takes place Red Cat (+)
Voltaic or Galvanic Cell Electrochemical Cell in which:
a spontaneous oxidation-reduction reaction produces electrical energy
Half-Cell A cell where only oxidation or only reduction takes place
An electrochemical cell must have two half-cells connected by a salt bridge
A half-cell will not work by itself Both half-cells are required
Salt Bridge 1) Allows electrical contact between the two half-cells
2) Prevents mixing of the two half- cell solutions
3) Allows ions to flow maintaining electrical neutrality
Determining the Redox Rxn & Voltage of an Electrochemical Cell
Identify all molecules & ions (reactants) that exist in the electrolytic cell
1) Determine all possible half- reactions that could occur in the system
2 ) Look up each half-rxn from the Std. Redox Tables
3) Record each half-rxn & its standard voltage
4) Save the oxidation half- rxn that has the highest voltage
5) Save the reduction half- rxn that has the highest voltage
6) Balance the electrons between the two half-rxns
7) Add the two half-rxns to obtain the full electrochemical reaction
7) Add the voltage of each half-rxn to obtain the std. voltage required
Voltaic Cell Problems
Determine all when a cell with a Cu electrode in CuCl 2(aq) is connected to a cell with a Zn electrode in ZnBr 2(aq)
Determine all when a cell with a Fe electrode in FeCl 3(aq) is connected to a cell with a Mn electrode in MnCl 2(aq)
Determine all when a cell with a Mg electrode in Mg(NO 3 ) 2(aq) is connected to a cell with a Au electrode in Au(NO 3 ) 3 (aq)
Electrolysis Using electricity to force a non- spontaneous electrochemical rxn
Electrolytic Cell Chemical cell where electrolysis is being performed
How to determine the Redox Rxn & voltage of an Electrolytic Cell
Identify all molecules & ions (reactants) that exist in the electrolytic cell
1) Determine all possible half- reactions that could occur in the system
2 ) Look up each half-rxn from the Std. Redox Tables
3) Record each half-rxn & its standard voltage
4) Save the oxidation half- rxn that has the highest voltage
5) Save the reduction half- rxn that has the highest voltage
6) Balance the electrons between the two half-rxns
7) Add the two half-rxns to obtain the full electrochemical reaction
7) Add the voltage of each half-rxn to obtain the std. voltage required
Determine the rxn that takes place when 1.5 V is passed through two Pt electrodes in a solution containing MgI 2(aq) & ZnCl 2(aq)
Determine the rxn that takes place when 2.5 V is passed through two Pt electrode in a solution of NaCl (aq) 0
Determine the rxn that takes place when 2.0 V& 9.65 A is passed for 2.5 Hrs through two Pt electrodes in a solution containing MnBr 2(aq) & AlF 3(aq)
Relating Equations G o = H o - T S o G o = -RTlnK eq G o = -nF E o
Nernst Equation E = E o - (RT/nF)lnQ for non-standard conditions
Determine the voltage of a cell with a silver electrode in 1.0 M AgNO 3 & an iron electrode in 0.10 M Fe(NO 3 ) 2 at 27 o C
Determine the voltage of a cell with a silver electrode in 1.0 M AgNO 3 & a zinc electrode in M Zn(NO 3 ) 2 at 27 o C
Determine the voltage of a cell with a copper electrode in 0.10 M CuNO 3 & a zinc electrode in 1.0 M Zn(NO 3 ) 2 at 27 o C
Electroplating & Electro-purifying
Electrolysis During electrolysis, oxidation & degradation would occur at the anode while reduction & electroplating would occur at the cathode
Current Formula Current = charge/unit time Amps = coul/sec Amount (mass, volume, moles, etc) can be determined from the charge
Calculate the mass of copper plated onto the cathode when a 9.65 mAmp current is applied to a solution of CuSO 4 for 5.0 minutes.
Calculate the years required to plate 216 kg onto the cathode when a 96.5 mAmp current is applied to a solution of AgNO 3
Calculate the current required to purify 510 kg of aluminum oxide in 5.0 hours
Calculate the time required to electroplate 19.7 mg of gold onto a plate by passing 965 mA current through a solution of Au(NO 3 ) 3
Calculate the time required to gold plate a 2.0 mm layer onto a 250 cm 2 by passing 965 mA current through a solution of Au(NO 3 ) 3 (D Au = 20 g/cm 3 )
Calculate the time required to purify a 204 kg of ore that is 60.0 % Al 2 O 3 by applying a 965 kA current through molten ore sample:
Calculate the time required to purify a 32 kg of ore that is 75.0 % Fe 2 O 3 by applying a 9.65 kA current through molten ore sample:
Determine the voltage of a cell with a silver electrode in 5.0 M AgNO 3 & an zinc electrode in 0.25 M Zn(NO 3 ) 2 at 27 o C