Activity Series

1
Activity Series

• lithium
• potassium
• magnesium
• aluminum
• zinc
• iron
• nickel
• lead
• HYDROGEN
• copper
• silver
• platinum
• gold

Oxidizes easily
More active
Reduces easily
Less active
2
Activity series

• More active metals will displace less active
  metal ions.
• Hydrogen is the reference point.
• Electrons will flow spontaneously from the
  stronger reducing agent to the stronger oxidizing
  agent.

3

• Will the following reactions occur ?
• Ag Cu
• Cu2 Ag
• Mg2 Zn
• Zn2 Mg
• Zn2 Cu
• Mg2 Li

• lithium
• potassium
• magnesium
• aluminum
• zinc
• iron
• nickel
• lead
• HYDROGEN
• copper
• silver
• platinum
• gold

Yes
No
No
Yes
No
Yes
The metal must be above (more active than) the
ion for it to be a spontaneous reaction.
4
Electrochemistry

• Chemical energy becoming electrical energy

5

• Current- the flow of electricity (amps)
• Potential difference- the force pushing the
  current (volts)
• Electrolyte- an ionic solution that can carry
  electric current.
• Spontaneous redox reactions produce this electric
  energy.

6
Voltaic Cell

• Anode
• attracts anions
• where oxidation occurs
• Cathode
• attracts cations
• where reduction occurs
• Salt bridge
• connects the two half cells
• contains a strong electrolyte

7
Two half cells connected by a salt bridge
8
Reduction half reactions
F2 is the strongest oxidizing agent
Li is the strongest reducing agent
9
Reduction Potentials (E)

• Eo is the standard electrode potential
• all ions are 1M and gases are 1 atm
• The net Eo is the sum of the Eo of the half
  reactions
• The stronger oxidizing agent reduces.
• Reverse the sign of the substance oxidized.
• If E is positive, the reaction is spontaneous.
• If E is negative, the reverse reaction is
  spontaneous.

10

• What is the voltage produced from the reaction of
  Zn metal with Cu2 ions?
• Zn(s) Cu2(aq) g Zn2(aq) Cu(s)
• Zn2 2e- g Zn -0.7628
• Cu2 2e- g Cu 0.3402
• -(-0.7628) 0.3402 1.103 volts
• Will happen spontaneously
• Zn2 Ni(s) g Zn(s) Ni2
• -(-0.23) (-0.7628) -.53
• Will not occur spontaneously

Cu2 will reduce!
11
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12
Faradays Law

• Coulombs amperes x seconds
• 1 C 1amp1sec
• 96,485 coulombs 1 mole e-

13
What mass of copper will be deposited by a
current of 7.89 amps flowing for 1200 seconds?

• Cu2 2e- g Cu at the cathode
• 7.89A x 1200s x 1C x 1 mol e- .0981 mol e-
• As 96,485C
• .0981 mol e- x 1 mol Cu x 63.5g Cu 3.1g Cu
• 2 mol e- 1 mole Cu

14
What mass of Cr3 is produced by a current of
0.713A flowing for 12,800 seconds?

• 14H3O 6Fe2 Cr2O72- g 6Fe3 2Cr3-21H2O
• .713A x 12,800s x 1C x 1 mol e- .0946 mol e-
• As 96,485C
• .0946 mol e- x 2mol Cr3 x 52.0g Cr3 1.64gCr3
• 6mol e- 1mol Cr3

15
Nernst Equation

• Eo Voltage under standard conditions
• (1M solutions at 25C and 101.3kPa)
• At non-standard conditions, use Nernst equation
• E E - 0.05916 log products
• n reactants
• n no. of electrons transferred
• Coefficients in front of reactants or products
  are used as powers of their concentrations.

16

• Determine the voltage of a
• Zn Zn2 (.75M) Ni2(2.0M) Ni cell at standard
  temperature and pressure.
• Eo 0.7626V -.257V .506V
• E .506V - .0592 log .75M
• 2 2.0M
• E .506V 0.0296 (log 0.375)
• E .506V (-0.0126)
• E .519V