3.1.11 Electrode Potentials And Electrochemical Cells

Question 1

Salt bridge

Answer 1

• normally filter paper saturated with sodium nitrate solution
• allows the flow of ions
• not made of wire - as would set up own electrode system
• why unreactive aq solution - so doesn’t react and mess experiments up

Question 2

Voltmeter

Answer 2

Incredibly high resistance
To prevent the current from flowing in the circuit.
Voltage = electrodpotential
If want electrons to flow = replace with bulb

Question 3

Reduction and oxidation in the cell (electron movement rule)

Answer 3

No voltmeter
Electrons more neg to more positive halfcell

Question 4

Half cell

Answer 4

Metal
Dipped in its aq solution/ ions
Normally metal sulphate aq

Question 5

NOPR rule

Answer 5

NO
PR

• more negative halfcell (more neg potentail difrence) = oxidised
• more positive halfcell = reduced

Question 6

When half cell is reduced half equation

Answer 6

When reduce start with the ion !!!
Then go to the atom

(Oposite for oxidised)

Question 7

Cell diagram

Answer 7

1. 2 vertices line in middle = salt bridge
2. Then next to the salt brifmdge - the most oxidised form (highest oxidation state
3. Single vertices lone = change of state

Best practice
More positive half cell = RHS
More negative half cell =LHS

Question 8

No solid conducting surface

Answer 8

Use a platinum electrode
- as need an electrode conducting surface
- platinum is unreactive
- conducts electricity
- changes the cell diagram
- do it normally but common between the two aq species and add py electrode on the end

Question 9

Reasons for the standard hydrogen electrode

Answer 9

Can not measure the electrode potential of one half cell
Can only calculate the potential difference
Standard hydrogen electrode - refrence electrode -0V

Question 10

Standard hydrogen electrode format

Answer 10

Platinum electrode
Solution needs proton often strong acid fully dissociated = eg HCl
H2 gas bubbled over the solution and electrode

Question 11

Standard hydrogen electrode equation

Answer 11

At eqm
Can be oxidised or reduced depending on the other electrode attached
H2 -> <- 2H+ +2e-

Question 12

Standard conditions for hydrogen electrode

Answer 12

H2 gas pressure 100kpa
Conc of H+ 1moldm3
Temp of 298K
Pt electrode

Question 13

Conventional cell dugram for the standard hydrogen electrode

Answer 13

Pt(S)/ H2(g) /H+(aq) //

Question 14

Standard hydrogen electrode trick to be carful of

Answer 14

When H2SO4 is the aq component
Diuretic base goes to 2mol H+
Meaning conc is NOT 1moldm-3
Needs to be 0.5 moldm-3

Question 15

Standard conditions

Answer 15

All ions in solution 1 mol dm-3( if 2 aq component they are still both qmoldm-3)
If gas pressure of 100kpa
Temp 298K
No surrent flowing

Question 16

Ecell =

Answer 16

= E reduced - E oxidised
= E right - E left

Question 17

Strongest reducing / oxidising agent in electrochemical series

Answer 17

For finding oxidised
The most positive and the atom on the left

For finding reducing agent
The most negative half cell the atom
The atom on tye top right

Question 18

Use electrode potential to explain why reaction takes place

Answer 18

Electrode potential of the(f2,f-) is greater than the electrode peotential (o2/h20)

this therfore f2 will oxidise the h20 to o2

Written as (f2/f-) as display halfcell = most oxidised form/ the next most oxidised form

Question 19

Changing of conditions of the cell

Answer 19

Increase concentration of reactant = increase Ecell (increase reduced )

Decrease the conc of reactant = decrease Ecell

Most electrode cells in the spontaneouse direction are in teh exothermic direction

Question 20

What is the electrochemical series

Answer 20

List of electrode potentials in numerical order

Question 21

Suggest why two tm complexes of same metal have different electrode potentials

Answer 21

Different ligands

Question 22

Why electrode potential of the standard hydrogen electrode is 0

Answer 22

By definition

Question 23

Conventional representation of the alkaline hydrogen oxygen fuel cell

Answer 23

Pt/H2(g)/OH-(aq)/H2O(l)
//
O2(g)/H2O(l)OH-(aq)/Pt

Question 24

Why the emf of a hydrogen oxygen file cell in acidic conditions is teh same as in alkaline

Answer 24

As the overall reaction is the same
2H2 + O2 -> 2H2O

Question 25

Hydrogen oxygen fule cell m overall equation

Answer 25

2H2 + O2 -> 2H2O

Question 26

Why hydrogen oxygen fule cell is not carbon neutral

Answer 26

Hydrogen is made using an energy source that is not carbon neutral

Question 27

Alkali hydrogen fule cell

Answer 27

hydrogen from the left
oxygen from the right

liberating electrons left to right

OH- electrolyte - eliminated in final equation but included in half equations

h2 looses electrons - oxidation
oxygen gains electrons - reduction

neg oxygen joining pos hydrogen

hydrogen and oxygen constantly being put in

Question 28

acidic hydrogen fule cell

Answer 28

no OH- electrolyte

presence of H+ in both half equations

overall reaction is the same as alkali

Question 29

The simplified electrode reactions in a lithium cell:

Answer 29

The simplified electrode reactions in a lithium cell:

Positive electrode: Li+ + CoO2 + e– → Li+[CoO2]–

Negative electrode: Li → Li+ + e–

Question 30

cells and batteries

Answer 30

Cells can be non-rechargeable (irreversible), rechargeable or fuel cells.

Fuel cells are used to generate an electric current and do not need to be electrically recharged.