1.11 Electrode Potentials

Question 1

why does a voltage form across two half cells?

Answer 1

• one half cell has a greater tendency to oxidise an ion and release electrons than the other
• more electrons will build up on one electrode
• creating a potential difference between the electrodes

Question 2

why do we use a high resistance voltmeter?

Answer 2

• to stop current from flowing in the circuit

Question 3

what is the salt bridge?

Answer 3

• connects the circuit
• should be unreactive with electrodes and electrode solution
• made from a piece of paper soaked in a salt solution

Question 4

what happens to the most positive electrode

Answer 4

• reduction, ions accept electrons

Question 5

what happens to the more negative electrode

Answer 5

• oxidiation, electrons are given off

Question 6

how does cell notation work?

Answer 6

• write both reduction equations for the elements
• determine which undergoes oxidation/reduction
• starting from left of cell, write the oxidation equation, then the reduction
• seperate with a salt bridge

Question 7

what happens if a system doesnt inclue a metal?

Answer 7

• use a platinum electrode

Question 8

why do we use a platinum electrode?

Answer 8

• inert
• provides conducting surface for electron transfer
• electrically conductive

Question 9

what is the standard hydrogen electrode used for?

Answer 9

• measures potential of all electrodes by comparing them to SHE
• SHE is assigned e potential of 0V

Question 10

what are the standard conditions required?

Answer 10

298K
100kPa

both ion solutions have to have a concentration of 1moldm^-3

Question 11

what will happen to the electrode potential if hydrogen ion concentration is reduced

2H+ + 2e > H2

Answer 11

• reducing H+ concentration causes equilibrium to shift to the left to reduce this change
• this will cause electrode potential to become more negative

Question 12

what is the equation for electrode potential?

Answer 12

E reduced - Eoxidised = Ecell

Question 13

give the oxygen electrode equation for ethanol fuel cells

Answer 13

O2 + 4H+ + 4e- > 2H2O

Question 14

give the ethanol electrode equation for ethanol fuel cells

Answer 14

C2H5OH+ 3H2O > 2CO2 + 12H+ + 12e

Question 15

why can ethanol be considered to be a carbon neutral fuel?

Answer 15

• ethanol can be made from renewable resources in a carbon neutral way
• absorbed in photosynthesis, released by combustion etc

Question 16

give the equation for the oxygen electrode and hydrogen electrode at hydrogen fuel cells

Answer 16

O2 + 2H2O + 4e > 4OH-

H2 + 2OH- > 2H2O + 2e

Question 17

what are some advantages of using ethanol fuel cells?

Answer 17

• less pollution and no CO2 emission
• greater efficiency