Electrode Potentials

Question 1

Writing redox reaction

Answer 1

Calculate oxidation states of each element present in equation
Use this to determine what is ox/reduced
Balance O with H2O and then H+
Add electrons to side to balance charges/ox states

Question 2

Manganate redox titrations

Answer 2

End point - permanent pink colour shows excess of MnO4- ions
Oxidising agent
Commonly to analyse Fe2+ ions and ethanedioic acid

Question 3

Electrochemical cells

Answer 3

Converts chemical to electrical energy
Require reaction when one species transfers electrons to another species

Question 4

Half cells

Answer 4

Chemicals present in redox half equation
Contains an electrode and an aqueous solution

Question 5

Metal metal ion half cells

Answer 5

Metal electrode in a solution of its aqueous metal ions
Half cell equation is in equilibrium
Forward is reduction vice versa

Question 6

Ion ion half cells

Answer 6

Contains same elements in different oxidation states
Eg aq Fe2+ & Fe3+
Inert metal electrode present

Question 7

Electrode potentials

Answer 7

More reactive metal releases electrons more readily and is oxidised -ve electrode
Less reactive gains electrons and is reduced positive

Question 8

Standard electrode potential

Answer 8

The emf of a half cell connected to a standard hydrogen half cell in standard conditions
Standard electrode (H) is exactly 0V

Question 9

More negative the electrode potential value

Answer 9

Greater tendency to lose electrons and undergo oxidation (reverse equation)
Greater reactivity of a metal

Question 10

More positive the Electrode pot value

Answer 10

Greater tendency to gain electrons - reduction (forward reaction)
Greater reactivity of non metal

Question 11

Electron flow

Answer 11

From most negative to most positive

Question 12

Calculating cell potential

Answer 12

Positive electrode - negative electrode

Question 13

Large +ve electrode potential

Answer 13

Half equation has strong tendency to go from left to right

Question 14

Predicting feasibility of equations

Answer 14

Write out half equations starting w most negative circle species reacting
EP left to right - EP right to left( don’t reverse sign) = EP reaction
If EP value is positive reaction will take place

Question 15

Limitations predicting reaction using EP

Answer 15

Reaction has a high activation energy therefore the rate is very slow
The reaction may not happen under standard conditions
EP values apply to aqueous equilibrium - many reactions don’t take place in aqueous conditions

Question 16

Primary cells

Answer 16

Non rechargeable - one use
Electrical energy is produced by oxidation and reduction at electrodes
Chemicals will be all used up
Alkaline based Zn/MnO2 and KOH electrolyte

Question 17

Secondary cells

Answer 17

Rechargeable - cell reaction can be reversed
Chemicals in cells regenerated
Car batteries lithium ion batteries - laptops

Question 18

Fuel cells

Answer 18

Energy from reaction of a fuel with O to create a voltage
Fuel and oxygen into the cell and products flow out electrolyte remains
Do not have to be recharged

Question 19

Alkali hydrogen fuel cell

Answer 19

Hydrogen and oxygen in
H2 + 2OH- -> 2H2O+ 2e-
1/2 O2 + H2O + 2e- -> 2OH-
H2 + 1/2O2-> H2O
1.23v

Question 20

Acid hydrogen fuel cell

Answer 20

H2 dissociates
O2 reacts with H+ forming water
1.23v

Question 21

Manganate equation

Answer 21

MnO4- + 8H+ => Mn2+ + 4 H2O