What is powering this clock?

1

• What is powering this clock?

2
How much Voltage

• You can see the battery is missing and the clips
  are attached to the terminals.
• What is the voltage required to run the clock?

3
Make a Battery
Place a drop of Copper nitrate on one end of the
paper. Place a piece of copper in the center of
the wet spot
4
Make a Battery
On the other end place a drop of zinc nitrate and
place a piece of zinc in the wet solution.
5
Make a Battery
Add a couple of drops of KNO3 in the middle of
the two solutions to make a salt bridge.
6
Make a Battery
Touch the probe leads to the two metals as
pictured here. Record the voltage.
V
7
Whats the sign?

• If the reading is negative, switch the leads to
  the other metals. You want to get a positive
  voltage reading.
• Record the metal that is at the red lead and the
  metal at the black lead.

8
REDUCE RED CATS

• This is the way I remember that reduction occurs
  at the cathode and it is at the red lead.
• Reduction ?
• Oxidation ?

9
Look at the Standard Reduction Potential Table

• Cu2
• Cu
• Zn2
• Zn

10
Find the voltage for each pair of metals you have.
?
11

• Cu2 2 e- ? Cu 0.34 volts
• Zn ? Zn2 2e- 0.76 volts
• 
  1.10 volts

12
What is the purpose of the salt bridge?
13

• What is powering this clock?

14
How much Voltage

• You can see the battery is missing and the clips
  are attached to the terminals.
• What is the voltage required to run the clock?

15

• After adding the phenolphthalein around the
  strip of magnesium a pink color is observed.
• Also there are tiny bubbles all along the sides
  of the magnesium

16
Lead Battery

• AnodePb(s) HSO4- ?PbSO4(s) H(aq) 2 e-
• cathode
• PbO2(s) 3 H HSO4 2e- ? PbSO4 H2O
• 0.296 V
• 1.628 V
• 1.924 V

17
Mercury Battery
STEEL cathode
HgO in KOH Zn(OH)2
Zn container anode
Watches, pacemakers, calculators
18
Rechargeable Nickel-cadmium

• anode Cd OH- ? Cd(OH)2 2 e-
• cathode NiO(OH)S H2O ?Ni(OH)2 OH-
• Recharge many times because the solid products
  adhere to the surface of the electrode renewing
  the battery.

19
Corrosion

• Corrosion is the oxidative deterioration of a
  metal such at rust.

O2 from the air
Drop of water
O2 4H 4 e- ? 2 H2O cathode
Fe --gt Fe2 2 e- anode
Rust
20
How can you prevent corrosion?

• Look at the equation and prevent the reaction
  from happening. What can you do?

21
Electrochemical Cells

• There are 2 types of cells
• Galvanic also called voltaic is a spontaneous
  reaction that produces an electric current
• - Electrolytic requires an outside source to
  supply the current such as a battery or
  electrical outlet

22
Electroplating

• Example of an Electrolytic cell
• Silverplated dinnerware - Silver is a soft metal
  what would happen if you used a solid silver
  fork?

23
Electrolysis

• Electrolysis

Black lead cathode -
Red lead anode
Graphite electrodes
Na2SO4(aq)
24
What is happening??

• Reduction
• 2 H2O(l) 2 - ? H2(g) 2 H-(aq) -0.83 V
• 2 H(aq) 3 e- ? H2(g) 0.00 V
  
• Na(aq) e- ? Na(s) -2.71
  V
• Oxidation
• 2 H2O ? O2(g) 4H(aq) 4e- -1.23 V
• 2 SO42- ? S2O8 2 e-
  -2.00 V

25
See bubbles? What is the clue?

• Look at the data table again and see which
  reactions you think took place

26
What is happening??

• Reduction
• 2 H2O(l) 2 - ? H2(g) 2 H-(aq) -0.83 V
• 2 H(aq) 3 e- ? H2(g) 0.00 V
  
• Na(aq) e- ? Na(s) -2.71
  V
• Oxidation
• 2 H2O ? O2(g) 4H(aq) 4e- -1.23 V
• 2 SO42- ? S2O8 2 e-
  -2.00 V

27
Answer

• Reduction was water or Na
• We know is must be water for 3 reasons -
• 1. a gas was produced
• 2. sodium reacts with water violently
• 3. It became more basic
• 2H2O 2 e- --gt H2(g) 2 OH- -.83V

28

• Oxidation was either water of sulfate ion
• Oxidation of water produces H and a gas. Do we
  have evidence of that?
• H2O --gt O2(g) 4 H 4 e- -1.23 V

29
Energy Involved

• 2H2O 2 e- --gt H2(g) 2 OH- -.83V
• H2O --gt O2(g) 4 H 4 e- -1.23 V
• 
  - 2.06 V
• What does the negative sign mean?

30
Change the electrodes to Copper
Black lead cathode -
Red lead anode
Copper electrodes
Na2SO4(aq)
31
What is happening??

• Reduction
• 2 H2O(l) 2 - ? H2(g) 2 H-(aq) -0.83 V
• 2 H(aq) 3 e- ? H2(g) 0.00 V
  
• Na(aq) e- ? Na(s) -2.71
  V
• Cu2 2 e- - ? Cu - 0.34 V
• Oxidation
• 2 H2O ? O2(g) 4H(aq) 4e- -1.23 V
• 2 SO42- ? S2O8 2 e-
  -2.00 V
• Cu(s) - ? Cu2 2 e- 0.34 V