Electrochemistry

Question 1

Oxidation/Reduction Numbers

Answer 1

Oxidation numbers: used to keep track of electrons in species
- the more electronegative atom gets its preferred ox #

Question 2

Oxidizing agent

Answer 2

• cause of oxidation in another species, it itself gets reduced

Question 3

Reducing agent

Answer 3

• causes reduction, it gets oxidize

Question 4

Balancing redox rxn using 1/2 method

Answer 4

Add H2Os, H+, and electrons
Multiply rxns to balance electrons if needed

Question 5

Random flow vs organized flow of electrons

Answer 5

Random flow:
- reactants are mixed
- electrons transferred directly from one species to another
- energy released as heat
Organized flow
- reactants are physically separated
- redox 1/2 rxns are coexisting in diff 1/2 cells
- electrons flow through conductor between cells
- energy released can be harnessed to do work

Question 6

Galvanic (voltaic) cells

Answer 6

• spontaneity produce electricity
• driving force: spont rxns at electrons
• start with table of standard reductions

Question 7

Cell line notations

Answer 7

• 1/2 cells divided by ||
• ox 1/2 rxn left side
• red 1/2 rxn right side
• electrodes on outside
• phase boundary represented by |
  Ox|ox+||red+|red

Question 8

Galvanic cell diagram

Answer 8

See notes
- red cat
- an ox

Question 9

Ecell solving

Answer 9

Ecell=Eox+Ered

Question 10

Actual potentials & Nernst Eq

Answer 10

E=Ecell-(RT/nF)ln(Q)
- if Q>1: E<Ecell, lnQ(+), more prod than react
- if Q<1: E>Ecell, lnQ(-), more react than prod
- if Q=K: E=Ecell, equilibrium

Question 11

Concentration cells

Answer 11

• galvanic cell in which 1/2 rxns are the same but in positive directions
• driving force: diff in conc, spont direction goes forward, equilibriating the conc
• ln([prod]/[react]) in Nernst

Question 12

Electrolytic cell

Answer 12

• driving force: external power supply driving a nonspont rxn to spont
• start with power supply symbol (see notes)

Question 13

Corrosion of free metals

Answer 13

• most metals are not found in their elemental form in nature
• most found as cations in ores which are reduced to get free metal (smelting)
• corrosion is spont ox back to ionic form

Question 14

Prevent corrosion

Answer 14

• cathodic protection: a metal with a lower Ered is preferentially ox protecting higher metal
• coatings: manmade(paint &/ plastic), self forming (Al & Mg form impenetrable oxide layers that prevent H2O & O2 from ox layers below
• alloys: homogeneous mixture of metals & other elements that retains metallic properties