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

Electrolytic Cell need electrical energy so NONSPONTANEOUS

Chemical Potential

Energy

ElectricalPotentialEnergy

Galvanic Cell

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?

anode catode

Battery in one.Electrons in galvanic flowing from – to +Electrons in electrylic flowing from + to -

Electrolytic Cella Fat Red Cat ate an Ox

Use Table J, but oppositeMore active metal = cathode = negative

Less active metal = anode = positive

Galvanic CellA Fat Red Cat ate an Ox

Use Table J More active metal = anode = negativeLess active metal = cathode = positive

e- e- e-

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

• Anode – Positive – Oxidation

A pox = a diseaseAnd electrolytic

cell behave differently like

they are diseased?!

Various types of electrolytic cells1. 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)

(l)

+

Na+

Cl-

Na+

Cl-

-

Na+ + 1e- NaCl- + Cl + 1 e-

Gain electronSo reduced So cathodelose electron

So oxidizedSo anode

BUT WAIT SOMETHING IS WRONG WITH OUR ANODE

22 2

e- e- e- e-

Various types of electrolytic cells2. 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. Electroplating • cathode = object to be

plated• anode - made of metal

want to plate on object• solution: contains ions of

plating metal

NO3-

NO3-

+-

Ag+ + 1e- Ag

Gain electronSo reduced So cathode

Ag Ag+ + 1e-

lose electronSo oxidizedSo anode

e- e- e- e-

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?

What do every one of these have in common?