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Topic: Electrolytic Cell Do now: p.19 in packet, cross out # 19 and do # 20 and #21. must label anode/cathode . Chemical rxns can produce electricity = galvanic (voltaic) cell OR Electrical energy used to carry out chemical reactions = electrolytic cell .

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Topic: Electrolytic CellDo now: p.19 in packet, cross out # 19 and do # 20 and #21. must label anode/cathode 


  • Chemical rxns can produce electricity

    = galvanic (voltaic) cell

    OR

  • Electrical energy used to carry out chemical reactions = electrolytic cell

Electrolytic Cell need electrical energy so NONSPONTANEOUS


Galvanic Cell

Chemical

Potential

Energy

Electrical

Potential

Energy

Electrolytic Cell

Galvanic cell is a battery

Electrolytic cell needs a battery


Electrolytic Cells

  • Nonspontaneous

  • Need battery or power supply

  • Consumes energy = endothermic


What’s the difference?

Battery in one.

Electrons in galvanic flowing from – to +

Electrons in electrylic flowing from + to -

e-  e-  e-

anode

catode

Electrolytic Cell

a Fat Red Cat ate an Ox

Use Table J, but opposite

More active metal = cathode = negative

Less active metal = anode = positive

Galvanic Cell

A Fat Red Cat ate an Ox

Use Table J

More active metal = anode = negative

Less active metal = cathode = positive


NONSPONTANEOUS

e- flow Anode to Cathode

But from + to –

(opposite then we’d think)

That’s why we use the battery

SPONTANEOUS

e- flow Anode to Cathode

from – to +

(just like we’d think)

That’s why it’s spontaneous

 e- e-  e-


A pox on electrolytic cells
A POX on Electrolytic Cells

  • Anode – Positive – Oxidation

A pox = a disease

And electrolytic cell behave differently like they are diseased?!


Various types of electrolytic cells
Various types of electrolytic cells

  • Fused Salt Cells – used to purify metals

    (Fused means melted = molten salt cell)

  • Add NaCl (s) and melt it

  • Now NaCl (l)

  • Why melt it?!

  • Why add CaCl2(s)??!

  • Na+1 is reduce to Na(l)

  • Na(l) is less dense then NaCl(l) so it floats on top

  • 20,000 tons of Na are produce this way in the US every year

Molten b/c need ions

Lowers MP – don’t need as much heat


Fused salt cell molten salt cell
Fused Salt Cell (Molten salt cell)

+

-

e- e- e- e-

Gain electron

So reduced

So cathode

Na+

Cl-

Na+

Cl-

lose electron

So oxidized

So anode

(l)

2

Cl-+  Cl + 1 e-

2

Na+ + 1e- Na

2

BUT WAIT SOMETHING IS WRONG WITH OUR ANODE


Various types of electrolytic cells1
Various types of electrolytic cells

2. Electroplating

A layer of a second metal is deposited on the metal electrode that acts as the cathode

  • Used to enhance the appearance of metal objects and protect them from corrosion.


Various types of electrolytic cells2
Various types of electrolytic cells

2. Electroplating

  • cathode = object to be plated

  • anode - made of metal want to plate on object

  • solution: contains ions of plating metal


+

-

lose electron

So oxidized

So anode

e- e- e- e-

Ag  Ag+ + 1e-

Gain electron

So reduced

So cathode

NO3-

Ag+ + 1e- Ag

NO3-


3 electrolysis of h 2 o
3. Electrolysis of H2O

H2 is produced at one electrode, O2 at the other.

2H2O + energy 2H2 + O2

Can you tell from the picture which electrode is producing H2?



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