redox Flashcards
how to find e.m.f. when given electrode potentials; also what sign will the answer be
E(cell) = E(RHS) - E(LHS); always positive
which side has the more negative electrode
left
what causes a metal to have a more negative electrode
more reactive metal => more -ve electrode
why is a salt bridge needed in a cell
to complete the circuit by allowing the flow of ions
what salt is usually used in a salt bridge
KNO3
explain, in terms of the relevant oxidation numbers, why this is a redox reaction (what form should the answer be in)
N is reduced from +5 to +4; O is oxidised from -2 to 0
if both ions in a half cell are aqueous, what is the electrode made of
platinum
what conditions are needed to measure standard electrode potential
298 K temperature; 100 kPa pressure; 1 M concentrations
what solution is used in a standard hydrogen electrode
any strong acid (e.g. HCl, HNO3) for the H+ ions
why are platinum electrodes porous
to increase surface area for reactions
a reaction is catalysed by porous platinum; what does this tell us about the reaction
it needs adsorption onto a surface; it involves breaking bonds
what is the purpose of the alkali in an alkaline fuel cell
electrolyte - allows the movement of ions between electrodes
which way are electrode half equations always written
as reductions
which electrode half equation is flipped when making the overall equation
the more negative one (more reactive metal so it gets oxidised instead of reduced)
oxygen half equation at cathode in a fuel cell
O2 + 4H+ + 4e- => 2H2O
