Chapter 23 - Redox and electrode potentials Flashcards
define oxidising agent
A species that removes electrons from the species being oxidised, itself is readily reduced
define reducing agent
A species that adds electrons to the species being reduced, itself is readily oxidised
equation for the iron/ manganate redox titration
MnO4- + 8H+ + 5Fe5+ –> Mn2+ + 5Fe3+ + 4H2O
colour change for iron/ manganate titration
colourless –> pale pink
equation for the iodine/ thiosulfate redox titration
2S203^2- + I2 –> 2I- + S4O6^2-
how to determine the endpoint of the iodine thiosulfate redox titration
add starch towards the end
colour change blue/black –> colourless
define standard electrode potential
The e.m.f of a half cell compared with a standard hydrogen half cell measured at 298K, 100kPa, and solution concentration of 1mol dm-3
function of salt bridge
connect solutions of two half cells allowing the flow of ions
example of a salt bridge
filter paper soaked in KNO3
how to find Ecell
E(forward/ positive) - E(backwards/ negative)
when is a reaction feasible in terms of Ecell
positive
limitations of using Ecell to determine feasibility
- kinetically stable reactants leading to a high activation energy
- the reaction may not have occurred under standard conditions
ΔG using Ecell
ΔG = -nFEcell
what is F
faraday’s constant
96500 C mol-1
what is a primary cell
non rechargeable cell based on irreversible reactions
redox system of a primary cell: oxidation
ZnO + H2O + 2e- –> Zn + 2OH-
redox system of a primary cell: reduction
2MnO2 + H2O + 2e- –> MnO3 + 2OH-
what is a secondary cell
rechargeable cell based on reversible reactions
how can the reactions of a secondary cell be reversed
application of a large external current
redox system of a secondary cell: oxidation
Cd(OH)2 + 2e- ⇌ Cd + 2OH-
redox system of a secondary cell: reduction
NiO(OH) + e- + H2O ⇌ Ni(OH)2 + OH-
why is the nickel- cadium system no longer used in secondary cells
Cd(s) is toxic
overall equation for hydrogen fuel cell
H2 + 0.5O2 –> H2O
what are fuel cells
use energy from reactions of fuel with oxygen to create a voltage
