Electrochemistry Quiz

Electrochemistry

• Electrochemistry is the study of processes involving the interconversion of electrical and chemical energy.
• Electrolysis is the decomposition of an electrolyte by an electric current. Positive ions are attracted by the cathode and negative ions are attracted to the anode. This involves oxidation at the anode and reduction at the cathode which depends on electron transfer at the electrodes.

Faraday's Laws of Electrolysis

• Faraday's First Law states the amount of substance deposited or evolved at an electrode is proportional to the quantity of electricity passed. W = ZIt
• Faraday's Second Law explains that the weights of different substances evolved/deposited are proportional to their chemical equivalents when the same quantity of electricity passes through different electrolytes. W1/E1 = W2/E2

Electrochemical Cells

• Galvanic/Voltaic cells produce electric current from spontaneous chemical reactions.
• Single electrode potentials signify the tendency of metals to become positively or negatively charged when placed in contact with their ions.
• Standard hydrogen electrode (SHE) is used as a reference. It is assigned a potential of zero under standard conditions. Measurement of standard electrode potential of other half-cells can be done using SHE.
• Factors like temperature and concentration affect electrode potential.
• The Nernst equation is applicable to correlation of free energy and cell emf.
• Electrochemical series is used to predict the spontaneity of a reaction.

Conductance

• Metallic Conductors: The movement of electrons results in no change to the overall chemical properties. Resistance increases with temperature and follows Ohm's law.
• Electrolyte Conductance: The movement of ions results in chemical changes. Resistance decreases with temperature and does not follow Ohm's law. Factors affecting electrolytic conduction include solute-solute interaction, solute-solvent interaction, temperature, viscosity, size of ions.

Specific, Equivalent, and Molar Conductance

• Specific Conductance (conductivity): The reciprocal of specific resistance (K=1/ρ), represented by unit Ω⁻¹ cm⁻¹.
• Equivalent Conductance( ^ eq): The conductivity of a solution containing 1 g equivalent of the solute when placed between two electrodes 1 cm apart. ^eq = Kx 1000/C
• Molar Conductance ( A m): The conductivity of a solution containing 1 mole of the solute when placed between two parallel electrodes of 1 cm apart. A m = x1000/M

Variation with Dilution

• Specific conductance decreases, as the number of ions per unit area decreases with dilution.
• Equivalent conductance and molar conductance of an electrolyte increases with dilution, but strongly electrolytes increases only slightly
• For strong electrolytes, molar conductivity approaches a constant maximum value as dilution approaches infinity.
• For weak electrolytes, molar conductivity approaches a constant value as dilution approaches infinity. This value cannot be obtained by extrapolating the curve.

Electrodes

• Standard Hydrogen Electrode (SHE) is the standard reference
• Calomel electrode and Weston cell are other electrodes used as reference electrodes.

Electrode Potentials

• Standard electrode potentials (E°) are measured under standard conditions.
• The higher the reduction potential value, the more likely an electrode is to undergo reduction.
• Nernst equation describes how electrode potential varies with concentration.

Galvanic Cells

• Diagram explanations of Zn/Cu galvanic cells and relevant electrochemical reactions.
• Salt bridges explanations in Galvanic cells
• Functions of salt bridge: Completing the circuit, maintaining electrical neutrality, preventing the mixing of electrolytes

Batteries

• Primary cells are not rechargeable (e.g., Leclanche cell, mercury cell)
• Secondary cells are rechargeable (e.g., Lead storage battery)

Fuel Cells

• Electro-chemical cells that require a continuous supply of reactants to keep functioning.
• Fuel cells are pollution free.

Corrosion

• Corrosion is the slow conversion of a metal to undesirable compounds, by reaction with moisture and other gases.
• Factors affecting corrosion: Reactivity of the metal, presence of moisture and air, presence of electrolytes (ions).
• Mechanism of corrosion: involves oxidation at the anode and reduction at the cathode.
• Prevention of corrosion: includes barrier protection (painting, oil/grease coatings, electroplating), sacrificial protection (using more reactive metals), and using antirust solutions.