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electrode potentials Flashcards

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1
Q

what is the process of oxidation and reduction expressed in terms of

A

electron transfer

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2
Q

oxidation

A

loss of electrons

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3
Q

reduction

A

gain of electrons

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4
Q

oxidation is an increase in

A

oxidation state

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5
Q

reduction is a decrease in

A

oxidation state

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6
Q

what can we work out by assigning oxidation states

A

which species have been oxidised and which have been reduced without writing half equations

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7
Q

oxidising agent

A

species that accepts electrons

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8
Q

reducing agent

A

species that donates electrons

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9
Q

example of an oxidising agent

A

halogens

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10
Q

example of a reducing agent

A

reactive metals

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11
Q

what does an electrochemical cell use the electron transfer which occurs during a redox reaction to do

A

produce electrochemical energy

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12
Q

what does each electrochemical cell consist of

A

2 half cells corresponding to the two half equations occurring in the redox reaction

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13
Q

what does a half cell consist of

A

two species of the same element in different oxidation states

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14
Q

what is the electrode in a copper half cell

A

solid copper

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15
Q

what is the solution in copper half cell

A

1 mol dm3 copper 2+ ions

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16
Q

what is the IUPAC convention for writing half equations for electrode reactions

A

to give them as an equilibrium reaction where the forward reaction is reduction

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17
Q

what must the half cells be connected via in order to make use of the electrical energy produced in a redox reaction

A

connected via an external circuit and a salt bridge

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18
Q

what is the circuit usually

A

a conducting wire

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19
Q

what flow through the wire

A

electrons

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20
Q

what does the salt bridge consst of

A

a strip of filter paper soaked in saturated potassium nitrate or potassium chloride solution

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21
Q

what flows through the salt bridge

A

ions

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22
Q

what are the electrodes connected to

A

a high resistance voltmeter

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23
Q

what does the voltmeter easure

A

electromotive force (emf) in volts

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24
Q

what is the emf

A

potential difference

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25
Q

what is the other name for emf

A

cell potential

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26
Q

what are the standard conditions are there for a half cell

A
  • 100kPa
  • 298K
  • solution of ions at 1moldm-3
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27
Q

which metal goes on the rhs

A

the more positive metal

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28
Q

which metal goes on the rhs in the standard copper-zinc cell

A

copper

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29
Q

why is the copper the positive electrode in the copper-zinc cell

A

because it is connected to the positive terminal of the voltmeter and so is the positive electrode

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30
Q

what is the IUPAC convention for cell diagrams

A

to draw the positive electrode as the half cell on the RHS (except when measuring standard electrode potential against hydrogen electrode when hydrogen always on left)

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31
Q

what occurs at the negative electrode

A

oxidation

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32
Q

what occurs at the positive electrode

A

reduction

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33
Q

where do electrons flow in cell

A

from negative electrode to positive electrode

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34
Q

what does the standard electrode potential of a half cell indicate

A

its tendency to lose/gain electrons

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35
Q

is it possible to measure the standard electrode potential of one half cell alone

A

no

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36
Q

what is used as a reference to measure standard electrode potential against

A

a primary standard

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37
Q

`what is the primary standard for measuring electrode potentials

A

the standard hydrogen electrode

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38
Q

what emf does the standard hydrogen electrode have by definition

A

0.00V

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39
Q

standard hydrogen electrode

A
  • H2 gas at 1 00kPa
  • 1 moldm-3H+ (aq)
  • 298K
  • Pt electrode
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40
Q

equation for standard hydrogen electrode

A

2H+ + 2e->< H2(g)

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41
Q

standard electrode potential

A

emf of a half cell compared with a standard hydrogen half-cell

measured at 298K, all solutions having conc of 1moldm-3 and all gases at a pressure of 100kPa

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42
Q

what is the standard electrode potential found by measuring

A

the voltage of a cell with the standard hydrogen half cell as one half cell and the half cell under investigation as the other

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43
Q

what gives the sign of the electrode potential

A

the polarity of the half cell relative to the hydrogen half cell

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44
Q

conventional representation of a cell: what does a vertical solid line indicate

A

a phase boundary eg between a solid and a solution

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45
Q

conventional representation of a cell: what does a double vertical line show

A

a salt bridge

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46
Q

conventional representation of a cell: which species for each half cell is written next to the salt bridge

A

the species with the highest oxidation state

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47
Q

conventional representation of a cell: where is the standard hydrogen half cell shown when measuring the standard electrode potential of a half cell

A

LHS

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48
Q

conventional representation of a cell: where is the positive electrode shown when showing any other electrochemical cell

A

RHS

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49
Q

conventional representation of a cell: where is the negative electrode shown when showing any other electrochemical cell

A

LHS

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50
Q

what is an ion/ion half cell

A

half cells in which both species are aqueous ions

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51
Q

what must an ion/ion half cell contain

A

both the oxidised and reduced species

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52
Q

what electrode is used in an ion/ion half cell

A

platinum

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53
Q

what are standard electrode potential values determined by

A

measurement against the standard hydrogen electrode

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54
Q

what are all reactions shown as in the electrochemical series

A

reductions

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55
Q

what can we determine looking at the electrochemical series

A

the relative reactivity of different species

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56
Q

metals react by losing what to form positive ions

A

electrons

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57
Q

what do reactive metals undergo more readily

A

oxidation

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58
Q

the most reactive metals will have the most negative

A

E0 values

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59
Q

what are the most reactive metals good at

A

being reducing agents

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60
Q

what is the correlation between negativity of E0 value of metal and tendency for species on RHS to lose electrons and be oxidised

A

more negative E0 value, greater tendency for species on RHS to lose electrons and be oxidised

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61
Q

how to non metals react

A

by gaining electrons to form negative ions

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62
Q

reactive metals undergo what more readily

A

reduction

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63
Q

most reactive non metals will have most positive what

A

E0 values

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64
Q

most reactive non metals are good at what

A

being oxidising agents

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65
Q

correlation between positivity of E0 value of non metal and tendency for species of LHS to gain electrons and be reduced

A

more positive E0 value, greater tendency for species on LHS to gain electrons and be reduced

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66
Q

what must a half cell be connected to to determine the electrode potential of it

A

the standard hydrogen electrode

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67
Q

what can be connected to generate an emf

A

any 2 half cells

68
Q

what is the cell potential the difference between

A

the standard electrode potentials of the two half cells

69
Q

what is chemical energy converted into in an electrochemical cell

A

electrical energy

70
Q

what does the emf drop to once the chemicals are used up

A

0.00v

71
Q

which half equation goes forwards

A

the one with the more positive e0 value- gains electrons

72
Q

which half equation goes backwards

A

the one with the more negative e0 value- loses electrons

73
Q

how to determine which reaction will occur in the cell or in a test tube

A

add the two half equations, making sure that the number of electrons lost equals number of electrons gained

74
Q

measuring electrode potential for a metal/metal ion half cell eg copper: equation

A

Cu2+ +2e- <> Cu(s)

75
Q

the conventional representation of a cell: what does a vertical solid line indicate

A

a phase boundary eg between a solid and a solution

76
Q

the conventional representation of a cell: a double vertical line shows the

A

salt briddge

77
Q

the conventional representation of a cell: the species with the highest ? for each half cell is written next to the salt bridge

A

oxidation state

78
Q

the conventional representation of a cell: when measuring the standard electrode potential of a half cell the standard hydrogen half cell is always shown on the

A

left hand side

79
Q

The conventional representation of a cell: on which side is the positive electrode shown

A

The RHS

80
Q

The conventional representation of a cell: on which side is the negative electrode

A

Left hand side

81
Q

The conventional representation of a cell: using what equation can the cell potential be calculated

A

E0RHS-E0LHS

82
Q

To measure E0 for ion/ion half cells: what are ion/ion half cells

A

Half cells in which both species are aqueous ions

83
Q

To measure E0 for ion/ion half cells: what must the half cells contain

A

Both the oxidised and reduced species

84
Q

To measure E0 for ion/ion half cells: what electrode is used

A

Platinum

85
Q

The electrochemical series: in what order can the standard electrode potential values determined by measurement against standard hydrogen electrode be placed in

A

Numerical order

86
Q

The electrochemical series: what are all reactions shown as

A

Reductions

87
Q

The electrochemical series: what can we determine by looking at electrochemical series

A

Relative reactivity of different species

88
Q

The electrochemical series: metals react by losing _____ to form ______ ions

A

Losing electrons to form positive ions

89
Q

The electrochemical series: reactive metals undergo what more readily

A

Oxidation

90
Q

The electrochemical series: the most reactive metals will have the most _______ E0 values

A

Negative

91
Q

The electrochemical series: the most reactive metals are good _______ agents

A

Reducing

92
Q

The electrochemical series: the more negative the E0 values the ________ the tendency for the species on the _____ to _____ electrons and be _______

A

The more negative the E0 the greater the tendency for the species on the RHS to lose electrons and he oxidised

93
Q

The electrochemical series: non metals react by ______ electrons to form ______ ions

A

Gaining electrons to form negative ions

94
Q

The electrochemical series: reactive non metals undergo ______ more readily

A

Reduction

95
Q

The electrochemical series: the most reactive non metals will have the most _____ E0 values

A

Positive

96
Q

The electrochemical series: the most reactive non metals are good ______ agents

A

Oxidising

97
Q

The electrochemical series: the more positive the E0 the _______ the tendency for the species on the _____ to _____ electrons and be _____

A

The more positive the E0 the greater the tendency for the species on the LHS to gain electrons and be reduced

98
Q

Measuring the emf of an electrochemical cell, required prac: how else can emf be determined other than using hydrogen electrode

A

Any two half cells can be connected to generate an emf

Cell potential = difference between standard electrode potentials of 2 half cells

99
Q

Using electrode potentials to predict chemical reactions: what is chemical energy converted to in an electrochemical cell

A

Electrical energy

100
Q

Using electrode potentials to predict chemical reactions: when did the emf drop to 0.00V in an electrochemical cell

A

Once the chemicals are used up

101
Q

Using electrode potentials to predict chemical reactions: how can we predict what reaction occurs

A

By looking at the E0 values of the two half cells

102
Q

Using electrode potentials to predict chemical reactions: which half equation gains electrons and what does this mean

A

The half equation with the more positive E0 value gains electrons, so goes forwards

103
Q

Using electrode potentials to predict chemical reactions: which half equation loses electrons and what does this mean

A

The half equation with the more negative E0 value loses electrons, so goes backwards

104
Q

Using electrode potentials to predict chemical reactions: what must be certified when adding the two half equations together

A

Number of electrons lost=number of electrons gained

105
Q

Change in mass of the electrode: why does the mass of the negative electrode decrease when a current is drawn

A

The metal will be oxidised to metal ions

106
Q

Change in mass of the electrode: what happens to the mass of the positive electrode and why

A

Increases as metal ions turn to metal

107
Q

The effect of concentration on the emf of a cell: what are the values of E0 measured under standard conditions of

A

100kPa, 298K, 1 mol dm-3

108
Q

The effect of concentration on the emf of a cell: what can be used to predict how concentration changes affect EMF

A

Le chateliers lrinciple

109
Q

The effect of concentration on the emf of a cell (eg Zn|Zn2+||Cu2+|Cu): what will happen if [Cu2+]>1moldm3

A
  • equilibrium shifts right
  • ECu more negative
  • Cu2+ gains more electrons
  • Ecell will increase- bigger difference in E
110
Q

The effect of concentration on the emf of a cell (eg Zn|Zn2+||Cu2+|Cu): what will happen if [Cu2+]<1moldm-3

A
  • equilibrium shift LHS
  • ECu less positive
  • Cu2+ will gain feevwr electrons
  • Ecell will decrease- cell has smaller difference in E
111
Q

The effect of concentration on the emf of a cell (eg Zn|Zn2+||Cu2+|Cu): what will happen if [Zn2+]>1mol dm-3

A
  • equilibrium will shift RHS
  • EZn less negative
  • Zn will release fewer electrons
  • Ecell will decrease as cell has smaller difference in E
112
Q

The effect of concentration on the emf of a cell (eg Zn|Zn2+||Cu2+|Cu): what will happen if [Zn2+] < 1moldm-3

A
  • equilibrium shift LHS
  • EZn become more negative
  • Zn will release more electrons
  • Ecell will increase as cell has a bigger difference in E
113
Q

if conditions are no longer standard what is cell potential written as as opposed to E0Cell

A

ECell

114
Q

Limitations of using electrode potentials tocpredict redox reactions

A
  • predictions using electrode potentials tell us about equilibrium but not RoR
  • many reactions in laboratory not done under standard conditions- will affect electrode potential vales
115
Q

Commercial applications of electrochemical cells: what 3 main types can cells be divided into

A
  • non- rechargeable cells
  • rechargeable cells
  • fuel cells
116
Q

Non rechargeable cells: how are they designed to be used only once

A

Reactions occurring in cells cannot he reversed

117
Q

Non rechargeable cells: what will happen when the chemicals are used up

A

The battery will go flat and the emf will fall to 0.00V

118
Q

Non rechargeable cells: used in

A

Smoke detectors and clocks

119
Q

Non rechargeable cells: overall equation of zinc and manganese dioxide cell when it discharged

A

2MnO2 + 2H2O + Zn > 2MnO(OH) + 2OH- + Zn2+

120
Q

Non rechargeable cells: function of porous separator

A

Allows ions to flow

121
Q

Non rechargeable cells: function of carbon rod

A

Allows electrons to flow

122
Q

Non rechargeable cells: why cell often leaks after being used for a long time

A

Zn used up as reaction proceeds

123
Q

Rechargeable cells: why can they be recharged

A

Reaction occurring in cell can be reversed and chemicals in cell regenerated

124
Q

Rechargeable cells: examples

A
  • lead/acid- cars
  • Ni/Cd- torches/radios
  • lithium/ion-phones, tablets, cameras etc
125
Q

Lithium ion cells: why are they light

A

Lithium is the least dense mental

126
Q

Lithium ion cells: reaction occurring at positive electrode

A

Co(IV) reduced to Co(III)

127
Q

Lithium ion cells: reaction occurring at negative electrode

A

Li(0) oxidised to Li(+1)

128
Q

Lithium ion cells: equation for discharge of cell

A

CoO2 + Li > Li+[CoO2]-

129
Q

Lithium ion cells: equation for recharging cell

A

Discharge reaction reversed

Li+[CoO2]- > CoO2 + Li

130
Q

The effect of concentration on the emf of a cell (eg Zn|Zn2+||Cu2+|Cu): what will happen if [Cu2+]<1moldm-3

A
  • equilibrium shift LHS
  • ECu less positive
  • Cu2+ will gain feevwr electrons
  • Ecell will decrease- cell has smaller difference in E
131
Q

The effect of concentration on the emf of a cell (eg Zn|Zn2+||Cu2+|Cu): what will happen if [Zn2+]>1mol dm-3

A
  • equilibrium will shift RHS
  • EZn less negative
  • Zn will release fewer electrons
  • Ecell will decrease as cell has smaller difference in E
132
Q

The effect of concentration on the emf of a cell (eg Zn|Zn2+||Cu2+|Cu): what will happen if [Zn2+] < 1moldm-3

A
  • equilibrium shift LHS
  • EZn become more negative
  • Zn will release more electrons
  • Ecell will increase as cell has a bigger difference in E
133
Q

if conditions are no longer standard what is cell potential written as as opposed to E0Cell

A

ECell

134
Q

Limitations of using electrode potentials tocpredict redox reactions

A
  • predictions using electrode potentials tell us about equilibrium but not RoR
  • many reactions in laboratory not done under standard conditions- will affect electrode potential vales
135
Q

Commercial applications of electrochemical cells: what 3 main types can cells be divided into

A
  • non- rechargeable cells
  • rechargeable cells
  • fuel cells
136
Q

Non rechargeable cells: how are they designed to be used only once

A

Reactions occurring in cells cannot he reversed

137
Q

Non rechargeable cells: what will happen when the chemicals are used up

A

The battery will go flat and the emf will fall to 0.00V

138
Q

Non rechargeable cells: used in

A

Smoke detectors and clocks

139
Q

Non rechargeable cells: overall equation of zinc and manganese dioxide cell when it discharged

A

2MnO2 + 2H2O + Zn > 2MnO(OH) + 2OH- + Zn2+

140
Q

Non rechargeable cells: function of porous separator

A

Allows ions to flow

141
Q

Non rechargeable cells: function of carbon rod

A

Allows electrons to flow

142
Q

Non rechargeable cells: why cell often leaks after being used for a long time

A

Zn used up as reaction proceeds

143
Q

Rechargeable cells: why can they be recharged

A

Reaction occurring in cell can be reversed and chemicals in cell regenerated

144
Q

Rechargeable cells: examples

A
  • lead/acid- cars
  • Ni/Cd- torches/radios
  • lithium/ion-phones, tablets, cameras etc
145
Q

Lithium ion cells: why are they light

A

Lithium is the least dense mental

146
Q

Lithium ion cells: reaction occurring at positive electrode

A

Co(IV) reduced to Co(III)

147
Q

Lithium ion cells: reaction occurring at negative electrode

A

Li(0) oxidised to Li(+1)

148
Q

Lithium ion cells: equation for discharge of cell

A

CoO2 + Li > Li+[CoO2]-

149
Q

Lithium ion cells: equation for recharging cell

A

Discharge reaction reversed

Li+[CoO2]- > CoO2 + Li

150
Q

Fuel cells: what does it use to create a voltage

A

Energy from the reaction of a fuel with oxygen

151
Q

Fuel cells: what flows into the fuel cell and what flows out

A

Fuel and oxygen flow into fuel cell and products flow out

152
Q

Fuel cells: what remains in the cell

A

The electrolyte

153
Q

Fuel cells: what can fuel cells operate continuously depending on

A

Provided the fuel and oxygen are supplied into cell

154
Q

Fuel cells: do fuel cells have to be recharged

A

No

155
Q

The alkaline hydrogen oxygen fuel cell: what are the cells two electrodes made out of

A

Porous Pt based material

156
Q

The alkaline hydrogen oxygen fuel cell: what are the two electrodes separated by

A

A semi permeable membrane

157
Q

The alkaline hydrogen oxygen fuel cell: what is the electrolyte

A

Sodium hydroxide solution

158
Q

The alkaline hydrogen oxygen fuel cell: which reaction takes place when hydrogen enters at the negative electrode

A

H2 + 2OH- > 2H2O + 2e-

159
Q

The alkaline hydrogen oxygen fuel cell: reaction taking place at positive electrode

A

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

160
Q

The alkaline hydrogen oxygen fuel cell: overall equation

A

2H2 + O2 > 2H2O

161
Q

Advantages of fuel cells: why are they more efficient

A

They convert more of their available energy into kinetic energy

162
Q

Advantages of fuel cells: what is the only waste product

A

Water

163
Q

Advantages of fuel cells: why do they not need to be recharged

A

They produce a continuous supply of energy so long as hydrogen and oxygen are supplied so they do not need to be recharged

164
Q

Disadvantages of fuel cells: what is the disadvantage relating to hydrogen being produced

A

Can be done by electrolysis of water but requires electricity- burning fossil fuels

165
Q

Disadvantages of fuel cells: why must hydrogen be handled carefully when stored and transported

A

It’s explosive and flammable

166
Q

Disadvantages of fuel cells: what is there nothing of relating to hydrogen fuel

A

No infrastructure to provide hydrogen fuel for cars

Chemistry (42 decks)

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