3.1 redox and standard electrode potential

define oxidation

loss of electrons

define reduction

gain of electrons

what is an oxidising agent?

substance which causes another species to be oxidised by taking electrons from it (it itself gets reduced)

what is a reducing agent?

substance which causes another species to be reduced by donating electrons to it (it itself gets oxidised)

what happens in displacement reactions?

more reactive metal replaces less reactive metal from a solution (because more reactive = stronger reducing agent)

what does a voltmeter do?

measures difference in strength of the 2 reducing agents

allows electrons to flow

what does a salt bridge do?

connects the 2 half cells, completing the circuit

allows ions to flow

what is a salt bridge saturated in?

potassium nitrate solution KNO3 (aq)

metal-metal ion half cell

metal placed in a solution of its ions

eg Cu (s) | Cu2+ (aq)

gas-gas ion half cell

gas bubbled into solution of its ions

eg Pt (s) | H2 (g) | H+(aq)

ion-ion half cell

inert metal conductor placed in solution of the same element in 2 different oxidation states

eg Pt (s) | Fe3+ (aq), Fe2+ (aq)

what does a more negative standard electrode potential mean?

stronger reducing agent

what does a more positive standard electrode potential mean?

weaker reducing agent

what are the standard conditions of the standard hydrogen electrode?

298K

1 atm

1 moldm-3

how to put half equations together for cells?

compare Eθ values

more negative = negative electrode

flip equation of more negative equation

add together

write the half and overall equations for a hydrogen fuel cell in acid conditions

H2 → 2H+ + 2e-

O2 + 4H+ + 4e- → 2H2O

2H2 + O2 → 2H2O

write the half and overall equations for a hydrogen fuel cell in alkaline medium

1/2O2 + H2O + 2e- → 2OH-

H2 + 2OH- → 2H2O + 2e-

1/2O2 + H2 → H2O

what are the advantages of hydrogen fuel cells?

do not produce CO2 (no contribution to global warming)

greater efficiency

convenient energy store

what are the disadvantages of hydrogen fuel cells?

difficult to store

hydrogen is explosive

use of toxic chemicals during production

how is the hydrogen in fuel cells generated?

CH4 + H2O → CO + 3H2