redox and electrode potentials Flashcards
what is an oxidation number?
a measure of the number of electrons that an atom uses to bond with atoms of another element
what is reduction?
gain of electrons
decrease in oxidation number
what is oxidation?
loss of electrons
increase in oxidation number
what is an oxidising agent?
a reagent that oxidises (takes electrons from) another species
it is reduced itself
what is a reducing agent?
a reagent that reduces (adds electrons to) another species
it is oxidised itself
steps for constructing redox equation
1 - identify reactants and products
2 - balance the elements which are oxidised or reduced and identify their change in oxidation number
3 - balance the change in oxidation number: total increase = total decrease
4 - check if any other element needs balancing
manganate (VII) titration colour change
purple MnO4- ions are reduced to very pale pink Mn2+ ions
iodine-thiosulfate titration equation
2 S2O3 2- (aq) + I2 (aq) → 2I- (aq) + S4O6 2- (aq)
what indicator is used for the iodine-thiosulfate titration?
add starch when solution is orange-brown coloured
the solution turns blue-black
as the thiosulfate is added, the solution starts to turn to straw colour
when the blue-black colour disappears, the reaction is complete
significance of standard electrode potential, Eθ, values
more positive Eθ value shows greater tendency to gain electrons and undergo reduction
more negative Eθ value shows greater tendency to lose electrons and undergo oxidation
what direction are the equations in the electrochemical series read in?
equations with more positive Eθ values undergo reduction and are read in the forward direction
what are standard conditions?
298K temperature
101kPa pressure
1.00moldm-3 concentration
what metal is used as the electrode in aqueous solutions?
Pt
because it is inert and is an electrical conductor
what is the standard electrode potential?
the e.m.f. of a half cell compared with a standard hydrogen half cell, measured at 298K, with solution
concentrations of 1mol dm-3 and a gas pressure of 101kPa
set up of an electrochemical cell
the half cells must be connected by a salt bridge
the cell potential is measured in volts from a voltmeter
how is standard cell potential calculated?
Eθcell = Eθreduction - Eθoxidation
value must always be positive
types of storage cells
primary (non-rechargeable)
secondary (rechargeable)
what is a fuel cell?
a fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage
redox equation for the hydrogen-oxygen fuel cell
H2 (g) + 1⁄2 O2 (g) ->H2O (l)
how are species classified in the electrochemical series?
species at the top of the series are the strongest oxidising agents
