Topic 20: Electrode Potentials

Question 1

Electrode potential

Answer 1

The voltage produced when a standard half-cell is connected to a standard hydrogen cell under standard conditions

Question 2

More negative electrode potential

Answer 2

Better reducing agent

Question 3

More positive electrode potential

Answer 3

Better oxidising agent

Question 4

Standard hydrogen electrode electrode

Answer 4

Platinum electrode

Question 5

Standard hydrogen electrode pressure

Answer 5

100KPa

Question 6

Standard hydrogen electrode temp

Answer 6

298K

Question 7

Standard hydrogen electrode conc

Answer 7

1moldm^-3 HCl (H+ in solution)

Question 8

Requirements of Standard hydrogen electrode

Answer 8

• Pt electrode
• 1 moldm^-3 conc. HCl (H+ in solution)
• 298K
• 100KPa
  (H2 gas bubbled in)

Question 9

Why use HCl for standard hydrogen electrode as solution?

Answer 9

Completely ionises (dissociates) in water as it is a strong acid, so the H+ can be used to set up the equilibrium of the reaction.

Question 10

What connects two half cells?

Answer 10

• Wire for electrons to pass through (connect V to measure EMF)
• Salt bridge for ions to move between the cells to complete the circuit

Question 11

Salt bridge made of

Answer 11

Paper soaked in KNO3 solution potassium nitrate

Question 12

EMF calc

Answer 12

Erhs - Elhs
(more positive) - (more negative)
ALWAYS RHS - LHS

Question 13

Meaning in convential representation of cells |

Answer 13

Phase boundary, only between different states

Question 14

Oxidised/ reduced in conventional representation of cells

Answer 14

Most oxidised closest to the middle
Most reduced further away
ROOR
So one being reduced on the right one being oxidised on the left
Hydrogen always goes on the left and include Pt

Question 15

Salt bridge in conventional representation of cells

Answer 15

||

Question 16

Why is Pt used for half cells with no solid

Answer 16

• unreactive
• metal so conducts electricity

Question 17

, Meaning in convential representation of cells

Answer 17

Between same state

Question 18

Electrode potential of H

Answer 18

0V

Question 19

Feasible EMF reaction

Answer 19

Positive EMF means feasible rxn

Question 20

Non- rechargeable cells advantages

Answer 20

• Cheaper
• Easy to use
• Portable easy to replace
• Work in wide range

Question 21

Non- rechargeable cells disadvantages

Answer 21

• Waste
• Leakages can occur
• Non-sustainable
• Toxic chemicals from landfill get into water

Question 22

Rechargeable batteries

Answer 22

Reversible reactions - check if need to know equations

Question 23

Rechargeable batteries advantages

Answer 23

• More energy efficient as charging takes less energy than making new batteries
• Longer life-span than non-rechargeable
• Recharged multiple times
• Can last longer on single charge than nr

Question 24

Rechargeable batteries disadvantages

Answer 24

• Cost more
• Need to be recharged regularly
• Non all appliances work with them
• Will eventually degrade

Question 25

Electrochemical series def

Answer 25

Various redox equilibria arranged in order of their standard electrode potentials

Question 26

Positive electrode of lithium ion cell

Answer 26

LiCoO2

Question 27

Negative electrode of lithium ion cell

Answer 27

Carbon

Question 28

Lithium ion cell negative electrode equation

Answer 28

Li ---> Li+ + e-

Question 29

Lithium ion cell positive electrode equation

Answer 29

Li+ + CoO2 + e- ---> Li+[CoO2]-

Question 30

Discharging equations for lithium ion cell

Answer 30

Reverse of charging

Question 31

Alkaline hydrogen- oxygen fuel cell equations MAYBE I DO NEED TO KNOW THIS? - dont need to know this "the electrode reactions in an alkaline hydrogen-oxygen fuel cell" i do need to know this

Answer 31

2H2(g) + 4OH-(aq) ---> 4H2O(l) + 4e- (occurs at negative electrode) O2(g) + 2H2O(l) + 4e- --->4OH-(aq) (occurs at positive electrode) Overall: 2H2(g) + O2(g) ---> 2H2O(l)

Question 32

Electrolyte of alkaline hydrogen oxygen cell

Answer 32

NaOH

Question 33

Glucose cell

Answer 33

???

Question 34

Why value of EMF different in reality

Answer 34

Non standard conditions

Question 35

Lithium ion cell arrangement

Answer 35

Layers of electrode sandwiched between solid electrolyte

Question 36

What is happening during lithium ion cell charging?

Answer 36

Electrons are forced through the external circuit, from positive to negative electrode at the same time lithium ions move through the electrolyte towards the positive electrode to maintain the balance of charge.

Question 37

How does alkaline hydrogen-oxygen fuel cell differ from normal oxygen and hydrogen reacting

Answer 37

Takes place at low temperature so no production of nitrogen oxides Only produces water as biproduct

Question 38

Economy of hydrogen cell

Answer 38

-Hydrogen comes from crude oil so - Need hydrogen filling stations - Hydrogen is a gas so hard to store and transport - highly flammable and takes up lots of space (gas)

Question 39

Cl2(g) + 2e− → 2Cl^- emf 1.36 weakest reducing agent?

Answer 39

Forwards rxn is reduction so reducing agent is Cl- (weak)

Question 40

State why a fuel cell does not need to be electrically recharged.

Answer 40

Reactants supplied continuously

Question 41

Suggest one advantage of using methanol, rather than hydrogen, in a fuel cell for use in cars.

Answer 41

Methanol (is liquid so) can be stored easily or transported easily

Question 42

what happens to emf when a bulb is attached

Answer 42

- exam answer - goes to 0v as the conc of ions in the two solutions become equal/same. - my waffle - (not able to flow between so rxn just happens without the balance of the other cell)

Question 43

explain how the electrode reactions can be used to generate an electric current

Answer 43

When you connect two half cells to form an electrochemical cell, electrons flow from the more negative electrode to the more positive electrode. A voltage is produced. An electrical current is created and electricity flows