Managing Resources: Electrons, Fuels and Materials as Resources
Moving and conserving resources
This domain treats electrons, fuels and materials as resources to be moved, stored and conserved. Electrochemistry is central: oxidation and reduction, galvanic cells with their anode (oxidation) and cathode (reduction), standard electrode potentials, E°cell = E°cathode − E°anode, cell notation and the salt bridge, and electrolysis with its applications in refining, electroplating and chlorine production. Faraday's laws connect charge, moles of electrons and mass deposited. Around this sit corrosion and its prevention (sacrificial anodes, coatings, alloying), energy resources and combustion, atom economy and percentage yield as efficiency measures, and recycling or water treatment as sustainability responses.
Traps
- Reversing the electrode-potential subtraction. Spontaneous cells need E°cell > 0.
- Multiplying E° by stoichiometric coefficients; electrode potentials are intensive and stay unchanged.
- Forgetting that in a galvanic cell the cathode is positive while in an electrolytic cell it is negative - reduction occurs at the cathode in both.
- Mixing up percentage yield (actual over theoretical) with atom economy (mass of desired product over total mass of reactants).
- Losing the mole ratio between electrons and metal in Faraday calculations.
Worked example
A current of 2.00 A passes through copper(II) sulfate solution for 30.0 minutes. Find the mass of copper deposited.
Q = It = 2.00 × 1800 = 3600 C. n(e⁻) = Q/F = 3600/96 500 = 3.73 × 10⁻² mol. Since Cu²⁺ + 2e⁻ → Cu, n(Cu) = 1.865 × 10⁻² mol. Then m = nM = 1.865 × 10⁻² × 63.55 = 1.19 g.