What is powering this clock ?
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Transcript of What is powering this clock ?
• What is powering this clock?
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?
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
Make a Battery
On the other end place a drop of zinc nitrate and place a piece of zinc in the wet solution.
Make a Battery
Add a couple of drops of KNO3 in the middle of the two solutions to make a salt bridge.
Make a Battery
VTouch the probe leads to the two metals as pictured here.
Record the voltage.
What’s 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.
REDUCE RED CATS
• This is the way I remember that reduction occurs at the cathode and it is at the red lead.
• Reduction ?
• Oxidation ?
Look at the Standard Reduction Potential Table
• Cu2+
• Cu
• Zn2+
• Zn
Find the voltage for each pair of metals you have.
?
• Cu2+ + 2 e- Cu 0.34 volts• Zn Zn2+ + 2e- 0.76 volts
• 1.10 volts
•
•
1.1volts
Cu(NO3)2
CuZn
Zn(NO3)2
What is the purpose of the salt bridge?
1.1volts
Cu(NO3)2
CuZn
Zn(NO3)2
• What is powering this clock?
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?
• 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
Lead Battery
Anode:Pb(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
Mercury Battery
STEEL cathode
HgO in KOH
Zn(OH)2Zn container
anode
Watches, pacemakers, calculators
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.
Corrosion
• Corrosion is the oxidative deterioration of a metal such at rust.
Drop of water
Fe --> Fe2+ + 2 e- anode
O2 from the air
O2 + 4H+ + 4 e- 2 H2O
cathode
Rust
How can you prevent corrosion?
• Look at the equation and prevent the reaction from happening. What can you do?
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
Electroplating
• Example of an Electrolytic cell– Silverplated dinnerware - Silver is
a soft metal what would happen if you used a solid silver fork?
Electrolysis
Electrolysis
BatteryRed lead +
anode
Black lead
cathode -
Graphite electrodes
Na2SO4(aq)
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
See bubbles? What is the clue?
• Look at the data table again and see which reactions you think took place
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
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- --> H2(g) + 2 OH- -.83V
• Oxidation was either water of sulfate ion
Oxidation of water produces H+ and a gas. Do we have evidence of that?
H2O --> O2(g) + 4 H+ + 4 e- -1.23 V
Energy Involved
2H2O + 2 e- --> H2(g) + 2 OH- -.83V
H2O --> O2(g) + 4 H+ + 4 e- -1.23 V
- 2.06 V
What does the negative sign mean?
Change the electrodes to Copper
BatteryRed lead +
anode
Black lead
cathode -
Copper electrodes
Na2SO4(aq)
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