Electrode Potentials

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Electrode Potentials
R W Grime Ripon Grammar School
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Zn2(aq) 2 e ? Zn(s)
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- electrode anode oxidation
electrode cathode reduction
electron flow
At this electrode the metal loses electrons and
so is oxidised to metal ions. These electrons
make the electrode negative.
At this electrode the metal ions gain electrons
and so is reduced to metal atoms. As electrons
are used up, this makes the electrode positive.
Zn
Cu
Zn ? Zn2 2 e- oxidation
Cu2 2 e- ? Cu reduction
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Standard Conditions
Concentration 1.0 mol dm-3 (ions involved in ½
equation)
Temperature 298 K
Pressure 100 kPa (if gases involved in ½
equation)
Current Zero (use high resistance voltmeter)
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S tandard H ydrogen E lectrode
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Emf E? E?right - E?left
E? E?right
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Pt(s) H2(g) H(aq) Cu2(aq) Cu(s)
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ROOR
Ni(s) Ni2(aq) Sn4(aq), Sn2(aq) Pt(s)
K(s) K(aq) Mg2(aq) Mg(s)
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ELECTRODE POTENTIALS Q1
Emf E?right - E?left
- 2.71 E?right - 0
E?right - 2.71 V
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ELECTRODE POTENTIALS Q2
Emf E?right - E?left
Emf - 0.44 - 0.22
Emf - 0.66 V
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ELECTRODE POTENTIALS Q3
Emf E?right - E?left
Emf - 0.13 - (-0.76)
Emf 0.63 V
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ELECTRODE POTENTIALS Q4
Emf E?right - E?left
1.02 1.36 - E?left
E?left 1.36 - 1.02 0.34 V
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ELECTRODE POTENTIALS Q5
Emf E?right - E?left
a) Emf 0.15 - (-0.25) 0.40 V
b) Emf 0.80 - 0.54 0.26 V
c) Emf 1.07 - 1.36 - 0.29 V
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ELECTRODE POTENTIALS Q6
Emf E?right - E?left
a) E?right 2.00 - 2.38 - 0.38 V
Ti3(aq) e- ? Ti2(aq)
b) E?left -2.38 - 0.54 - 2.92 V
K(aq) e- ? K(aq)
c) E?right - 3.19 0.27 - 2.92 V
Ti3(aq) e- ? Ti2(aq)
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ELECTRODE POTENTIALS Q7
a) Cr(s) Cr2(aq) Zn2(aq) Zn(s)
Emf -0.76 - (-0.91) 0.15 V
b) Cu(s) Cu2(aq) Fe3(aq),Fe2(aq) Pt(s)
Emf 0.77 - 0.34 0.43 V
c) Pt(s) Cl-(aq) Cl2(g)
MnO4-(aq),H(aq),Mn2(aq) Pt(s)
Emf 1.51 1.36 0.15 V
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GOLDEN RULE

• The more ve electrode gains electrons
• ( charge attracts electrons)

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0
ve electrode
ve electrode
e
1.10 V
0.34 V
Cu2 2 e- ? Cu
0.76 V
Zn2 2 e- ? Zn
Cu2 Zn ? Cu Zn2
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PREDICTING REDOX REACTIONS Q1


0
ve electrode
ve electrode
e
0.51 V
0.25 V
Ni2 2 e- ? Ni
0.76 V
Zn2 2 e- ? Zn
Ni2 Zn ? Ni Zn2
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PREDICTING REDOX REACTIONS Q2
0

ve electrode
ve electrode
e
0.46 V
0.80 V
Ag e- ? Ag
0.34 V
Cu2 2 e- ? Cu
2 Ag Cu ? 2 Ag Cu2
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PREDICTING REDOX REACTIONS Q3 a
Mg(s)Mg2(aq)V3(aq),V2(aq)Pt(s)
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ve electrode
ve electrode
e
2.10 V
0.26 V
V3 e- ? V2
2.36 V
Mg2 2 e- ? Mg
YES Mg reduces V3 to V2
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PREDICTING REDOX REACTIONS Q3 b

0
ve electrode
ve electrode
e
0.59 V
1.36 V
Cl2 2 e- ? 2 Cl-
0.77 V
Fe3 e- ? Fe2
NO Cl- wont reduce Fe3 to Fe2
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PREDICTING REDOX REACTIONS Q3 c
Pt(s)Br-(aq),Br2(aq)Cl2(g)Cl-(aq)Pt(s)

0
ve electrode
ve electrode
e
0.27 V
1.36 V
Cl2 2 e- ? 2 Cl-
1.09 V
YES Cl2 oxidises Br- to Br2
Br2 2 e- ? 2 Br-
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PREDICTING REDOX REACTIONS Q3 d
Sn(s)Sn2(aq)Fe3(aq),Fe2(aq)Pt(s)


0
ve electrode
ve electrode
e
0.91 V
0.77 V
Fe3 e- ? Fe2
0.14 V
Sn2 2 e- ? Sn
YES Sn reduces Fe3 to Fe2
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PREDICTING REDOX REACTIONS Q3 e

0
ve electrode
ve electrode
e
0.03 V
1.36 V
1.33 V
Cl2 2 e- ? 2 Cl-
Cr2O72- 14 H 6 e- ? 2 Cr3 7 H2O
NO H/Cr2O72- wont oxidise Cl- to Cl2
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PREDICTING REDOX REACTIONS Q3 f
Pt(s)Cl-(aq)Cl2(g)MnO4- (aq),H(aq),Mn2(aq)P
t(s)

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ve electrode
ve electrode
e
0.03 V
1.51 V
1.36 V
MnO4- 8 H 5 e- ? Mn2 4 H2O
Cl2 2 e- ? 2 Cl-
YES H/MnO4- oxidises Cl- to Cl2
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PREDICTING REDOX REACTIONS Q3 g
Fe(s)Fe2(aq)H(aq)H2(g)Pt(s)
0

ve electrode
ve electrode
e
0.44 V
0.00 V
2 H 2 e- ? H2
0.44 V
Fe2 2 e- ? Fe
YES H oxidises Fe to Fe2
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PREDICTING REDOX REACTIONS Q3 h
0

ve electrode
ve electrode
e
0.34 V
0.34 V
Cu2 2 e- ? Cu
0.00 V
2 H 2 e- ? H2
NO H wont oxidise Cu to Cu2
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PREDICTING REDOX REACTIONS Q4

0
1.36 V
Cl2 2 e- ? 2 Cl-
1.51 V
0.77 V
MnO4- 8 H 5 e- ? Mn2 4 H2O
Fe3 e- ? Fe2
NO
1.33 V
YES
Cr2O72- 14 H 6 e- ? 2 Cr3 7 H2O
NO
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PREDICTING REDOX REACTIONS Q5a
0

ve electrode
ve electrode
2.19 0.34 - E?left
E?left 0.34 2.19 1.85 V
e
2.19 V
0.34 V
Cu2 2 e- ? Cu
? V
Be2 2 e- ? Be
Be2 Cu ? Be Cu2
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PREDICTING REDOX REACTIONS Q5b

0
ve electrode
ve electrode
When using SHE
E? cell emf 1.90 V
e
1.90 V
0.00 V
2 H 2 e- ? H2
? V
Th4 4 e- ? Th
4 H Th ? 2 H2 Th4
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PREDICTING REDOX REACTIONS Q6a
Pt(s)H2(g)H(aq)Br2(aq),Br-(aq)Pt(s)

0
ve electrode
ve electrode
e
1.09 V
1.09 V
Br2 2 e- ? 2 Br-
0.00 V
2 H 2 e- ? H2
H2 Br2 ? 2 H 2 Br-
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PREDICTING REDOX REACTIONS Q6b
Cu(s)Cu2(aq)Fe3(aq),Fe2(aq)Pt(s)

0
ve electrode
ve electrode
e
0.43 V
0.77 V
Fe3 e- ? Fe2
0.34 V
Cu2 2 e- ? Cu
2 Fe3 Cu ? 2 Fe2 Cu2