electrode potential

Question 1

what compound can be used for salt bridge?

Answer 1

KNO3

Question 2

why is KNO3 suitable for salt bridge?

Answer 2

unreactive and allows flow of ions

Question 3

why might current produced fall to zero at some point

Answer 3

all reactants used up

Question 4

what will happen to a cell once all reactants used up?

Answer 4

stops working or starts to leak

Question 5

why is platinum a suitable electrode?

Answer 5

it’s unreactive and conducts electricity

Question 6

E° means

Answer 6

-standard electrode potential
-means one electrode will be standard hydrogen electrode

Question 7

all electrode equations are shown as…

Answer 7

..reductions

Question 8

The E° of Cu2+/Cu is 0.37V. Why might the electrode potential of the following cell not be 0.37V?

Answer 8

“named solution” not 1 mol dm-3 concentration
not 298K temperature
not 100kPa pressure

Question 9

Explain why Ag+(aq) ions react with Li(s)?

Answer 9

E° of Ag+(aq) > E° of Li(s)
Ag+ is stronger oxidising agent than Li(s)

Question 10

what happens when Li+ is added to Ag?

Answer 10

E° of Ag(s) > E° Li+(aq)
Li+ cannot oxidise Ag

Question 11

how to calculate E cell?

Answer 11

E cell = Red-ox
E cell= more positive - least positive

Question 12

When is reaction feasible so that it can discharge?

Answer 12

when the E cell is positive
this means it produced current

Question 13

adv of using rechargeable cells

Answer 13

metals are reused

Question 14

disadv of using rechargeable cells

Answer 14

mains elecricity used to recharge
which may come from combusting fossil fuels
which releases CO2(g)

Question 15

how does E.M.F. changes when the concentration of Mg2+ changes?

(cell of Mg/Mg2+ and Fe2+/Fe)

Answer 15

-E.M.F. increases
-Mg equilibirum shifts to the left
-more electrons donated by Mg
-EMF=RED-OX
-so EMF gets bigger

Question 16

in which directions would the elctrons flow in the above cell?

Answer 16

-Cu2+ on left more concentrated than Cu2+ on the right
-equilibrium shifts to the left
-left electrode is positive electrode
-right electrode is negative electrode
-therefore electrons flow from right to left

Question 17

Lithium cell equations

Answer 17

positive electrode: Li+ + CoO2 + e- -> Li+[CoO2]-

negative electrode: Li-> Li+ + e-

Question 18

conventional cell represetation of Lithium

Answer 18

Li|Li+ ‖ Li+,CoO2|Li(CoO2)|Pt

Question 19

recharging Lithium cell overall equation

Answer 19

reverse direction of lithium cells equations and join them:
Li+ + CoO2 + e- <- Li+[CoO2]-
Li<- Li+ + e-

Li(Co2) -> CoO2 + Li

Question 20

where is oxygen in fuel cells

Answer 20

always on the right side
always reduced

Question 21

adv of using fuel cell and not fossil fuels

Answer 21

-greater efficiency
-less-polluting as water is the only product

Question 22

disadv of using fuel cell and not fossil fuels

Answer 22

H2 difficult to store
fossil fuels birned to produce hydrogen, which releases CO2

Question 23

adv of fuel cells compared to other cells

Answer 23

voltage is constant
as O2 and H2 supplied constantly
so concentration of reactants remains constant

Question 24

hydrogen fuel cell in acidic condition at the:
anode
cathode
overall equation

Answer 24

Question 25

hydrogen fuel cell in alkaline condition at the: anode cathode overall equation

Answer 25

Question 26

hydrogen-oxygen fuel conventional cell representation

Answer 26

Pt|H2|OH-,H2O ‖ O2|H2O,OH-|Pt

Question 27

in alkaline hydrogen fuel cell, how does increasing pressure of oxygen affect E.M.F.?

Answer 27

EMF increases as O2 equilibrium shifts to the right More electrons gained by oxygen