Chem 311 - Electroanalytical Chemistry

Electroanalytical Chemistry Definition (QCA)

Branch of analytical chemistry that uses electrical measurements of chemical systems for analytical purposes.

Electroanalytical Chemistry Definition (IUPAC 2019)

Analytical methods in which electrochemical processes or phenomena are the core of the measurement principle.

Chemical Process Core of Electrochemistry

Movement of electrons involving oxidation and reduction processes (redox reactions) producing changes in voltage, current, or resistance.

Ohm's Law

E = i * R, where E is electrical potential (voltage in Volts, V), i is electrical current (in Amperes, A), and R is electrical resistance (in Ohms, Ω).

Standard State Symbol (E°)

The superscript circle (° or ⦵) denotes thermodynamic standard-state conditions (typically 298.15 K, 1 bar pressure for gases, and 1 M solute concentration/unit activity).

Origin of Chemical Potentials

Arises from an accumulation or deficit of electric charge (buildup of electrons) produced by separated chemical reduction and oxidation half-reactions.

Electrochemical Half-Reactions at Electrodes

Oxidation occurs at the anode (loss of electrons; e.g., Fe -> Fe2+ + 2e-); reduction occurs at the cathode (gain of electrons; e.g., Cu2+ + 2e- -> Cu).

Standard Reduction Potential Reference Point

All tabulated standard reduction potentials are universally measured relative to the Standard Hydrogen Electrode (SHE), which is defined as E° = 0.00 V.

Relationship Between Reduction and Oxidation Potentials

An oxidation potential is obtained directly from the corresponding reduction potential by reversing the reaction equation and flipping the mathematical sign (E°_ox = -E°_red).

Galvanic Cell

An electrochemical cell in which two half-cells are connected via a salt bridge and external circuit, allowing a spontaneous chemical redox reaction to generate a potential difference and power an external electrical load.

Cell Voltage (Potential Difference) Meaning

The difference in electric potential between two electrodes (E_cell = E_cathode - E_anode), acting as a thermodynamic measure of the driving force or tendency of species to be reduced versus oxidized.

Electrical Work and Potential Difference

Work = charge * potential difference (1 Joule = 1 Coulomb * 1 Volt; w = q * E).

Standard Line Cell Notation Order

Written from left to right as: Anode | Reactants & Products || Reactants & Products | Cathode.

Cell Notation Formatting Conventions

Single vertical lines (|) denote phase boundaries; double vertical lines (||) denote the salt bridge; commas or semicolons separate species in the same phase; solute concentrations or gas pressures are shown in parentheses (e.g., (1 M) or (1 bar)); electron flow moves from left (anode) to right (cathode).

Standard Cell Potential and Free Energy Relation

ΔG° = -n * F * E° (or ΔG = -n * F * E for non-standard states), where n is the number of moles of electrons transferred and F is Faraday's constant.

Faraday's Constant (F)

The electric charge carried by one mole of electrons, approximately equal to 96,485 C/mol (96485.33 C/mol).

Spontaneity Criterion for Cell Potential

A reaction is spontaneous when ΔG < 0, which corresponds mathematically to a positive cell potential (E_cell > 0).

Equilibrium Constant and Standard Potential Relation

ΔG° = -R * T * ln(K) = -n * F * E°; rearranged gives E° = (R * T / (n * F)) * ln(K) or K = exp(n * F * E° / (R * T)), linking redox equilibrium directly to standard potential.

Nernst Equation (Natural Log Form)

E = E° - (R * T / (n * F)) * ln(Q), where R is the ideal gas constant (8.314 J/(mol*K)), T is temperature in Kelvin, and Q is the reaction quotient.

Nernst Equation (Base-10 Form at 298.15 K)

E = E° - (0.05916 V / n) * log10(Q), derived by converting ln(Q) to 2.3026 * log10(Q) at 25 °C.

Chemical Activity in Nernst Expressions

The reaction quotient Q must be expressed strictly in terms of thermodynamic activities (A_x = gamma_x * [X]) rather than raw molar concentrations.

Potentiometry

An electroanalytical technique where the electrical potential (E) of an electrochemical cell is measured under conditions of zero current flow (i = 0).

Amperometry

An electroanalytical technique where the electrical current (i) flowing through an electrochemical cell is measured while holding the electrode potential (E) constant.

Voltammetry

An electroanalytical technique where electrical current is measured as a function of time (i = f(t)) while systematically varying the applied electrode potential over time (E = f(t)).

Direct Coulometry

An electroanalytical technique where the total electric charge passed (Q = integral of i(t) dt) is measured while holding the electrode potential constant (E = constant) to exhaustively convert analyte.

Conductometry

An electroanalytical technique based on measuring the electrical conductivity of an electrolyte solution.

Impedimetry

An electroanalytical technique measuring the electrical impedance of a system subjected to a constant potential combined with a small-amplitude time-dependent perturbation (E = constant + f(t)).