• 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