The Electrolytic Cell

The Electrolytic Cell


• In the electrolytic cell, a nonspontaneous redox reaction is forced to occur by the use of a source of electricity.

• In the electrolytic cell, electrons are FORCED to flow from the positive electrode to the negative electrode!

• In the electrolytic cell, the cathode has a negative charge and the anode has a positive charge!


• Electrolytic cells are used to purify highly reactive elements from their compounds!

• Na0 (sodium) never exists pure in nature!• Pure sodium can be extracted from NaCl by

using an electrolytic cell.


Ex.1)

• Electrons always flow out of the negative pole of an electric source such as a battery.

• Electrons always flow towards the cathode.

battery+ -

NaCl(l)

e-

cathodeanode

Put a + on the positive

electrode and a - on the negative

electrode.

+ -


Ex.1)

Write the reduction half reaction: ______________________

Write the oxidation half reaction: ______________________

battery+ -

NaCl(l)

e-

cathodeanode

Cl1- → Cl20 + 2 e-2

Na1+ → Na0+ 1 e-2 2 2

+1 -1

Na Cl2

0 0


Ex.1)

_______________________________[write the balanced redox reaction]

battery+ -

NaCl(l)

e-

cathodeanode

+1 -1

Na Cl2

0 0

Na1+ Na0Cl1- → Cl2022 2+ +


Ex.1)

a) The electrode on the left is the ____ode and the

electrode on the right is the ____ode.

battery+ -

NaCl(l)

e-

+1 -1

Na Cl2

0 0

an

cath


Ex.1)

b) The positive electrode is on the __________ and the

negative electrode is on the __________.

battery+ -

NaCl(l)

e-

+1 -1

Na Cl2

0 0

leftright


Ex.1)

c) Write the half reaction that occurs at the electrode on

the left.

battery+ -

NaCl(l)

e-

+1 -1

Na Cl2

0 0

_________________________________________Cl1- → Cl20 + 2 e-2


Ex.1)

d) Write the half reaction that occurs at the electrode on

the right.

battery+ -

NaCl(l)

e-

+1 -1

Na Cl2

0 0

_________________________________________Na1+ → Na0+ 1 e-


Ex.2)



battery +-

KBr(l)

e-

cathode anode



electrode.

+-


Ex.2)

Write the reduction half reaction: ______________________

Write the oxidation half reaction: ______________________

battery

Br1- → Br20 + 2 e-2

K1+ → K0+ 1 e-2 2 2

+1 -1

K Br2

0 0

cathode anode

e-

KBr(l)

- +


Ex.2)


battery

+1 -1

K Br2

0 0

K1+ K0Br1- → Br2022 2+ +

e-

cathode anode

KBr(l)

- +


Ex.2)



battery

+1 -1

K Br2

0 0

- +

KBr(l)

cath

an


Ex.2)



battery

+1 -1

K Br2

0 0

e-

KBr(l)

- +

right

left


Ex.2)

c) Write the half reaction that occurs at the electrode on

the left.

battery

+1 -1

K Br2

0 0

e-

- +

KBr(l)

_________________________________________K1+ → K0+ 1 e-


Ex.2)

d) Write the half reaction that occurs at the electrode on

the right.

battery

+1 -1

K Br2

0 0

+e-

-

KBr(l)

_________________________________________Br1- → Br20 + 2 e-2


Ex.3)



battery +-

H2O(l)

e-

cathode anode



electrode.

+-


Ex.3)


battery

+1 -2

H2 O2

0 0

H2O H20→ O2

02 2 +

e-

cathode anode- +

H2O(l)


Ex.3)



battery

+1 -2

0 0

- +

H2O(l)

H2 O2

cath

an


Ex.3)



battery

+1 -2

0 0

e-

- +

H2O(l)

H2 O2

right

left


Ex.3)

c) What substance is produced at the electrode on

the left? ____________________

battery

+1 -2

0 0

e-

- +

H2O(l)

H2 O2

Hydrogen gas


Ex.3)

d) What substance is produced at the electrode on

the right? ____________________

battery

+1 -2

0 0

e-

- +

H2O(l)

H2 O2

Oxygen gas


Ex.3)

e) Why must a small amount of electrolyte (such as anacid) be added to the water in order for the

electrolytic decomposition to work?

___________________________________________________________________

battery

+1 -2

0 0

e-

- +

H2O(l)

H2 O2

because pure water does

not conduct electricity, so an electrolyte is added.


Ex. (4) Which half-reaction correctly represents the reduction of a potassium ion?

(1) K+ + e- → K (3) K+ → K + e-

(2) K + e- → K+ (4) K → K+ + e-

Ex. (5) Given the equation:

2 Al + 3 Cu2+ → 2 Al3+ + 3 Cu

The oxidation half-reaction is

(1) Al → Al3+ + 3e- (3) Al + 3e- → Al3+

(2) Cu2+ + 2e- → Cu (4) Cu2+ → Cu + 2e-


Ex. (6) During the electrolysis of molten cesium chloride (CsCl), pure cesium is produced at the

(1) positively charged cathode and pure chloride gas is produced at the negatively charged anode

(2) negatively charged cathode and pure chloride gas is produced at the positively charged anode

(3) positively charged anode and pure chloride gas is produced at the negatively charged cathode

(4) negatively charged anode and pure chloride gas is produced at the positively charged cathode

The Electrolytic CellEx. (7) Given the voltaic cell:

Pb(s) + Cu2+(aq) → Pb2+

(aq) + Cu(s)

The electrons will flow from (1) the Pb(s) electrode to the Cu(s) electrode (2) the Cu(s) electrode to the Pb(s) electrode (3) the Pb2+

(aq) electrode to the Cu(s) electrode (4) the Cu2+

(aq) electrode to the Pb(s) electrode

Ex. (8) What is conserved during all chemical reactions? (1) mass, only (3) both mass and charge (2) charge, only (4) neither mass nor charge

+ Battery -e-

Molten NaCl(ℓ)

e-

Na+

Na+

Na+

Na+

Na+

Cl-

Cl-

Cl-

Cl-

Cl-

Cl20

Na0

CathodeAnode

-+

2 NaCl 2 Na + Cl2

Reduction: 2 Na+1 + 2e- 2 Na0

Oxidation: 2 Cl-1 Cl20 + 2 e-

Na0


Na0

Na0

Na0

Na0

Na0

Na0

Na0

Na0 Na0

Na0Na0

Na0

Na0

Molten Na(ℓ)

Na0

Na0

Na0

Na0

Na0

+ Battery -e-

aqueous CuBr2(aq)

e-

Cu+2

Cu+2

Cu+2

Br-

Br-

Br-

Br-

H2O

Br20

Cu0

CathodeAnode

-+

CuBr2 Cu + Br2

Reduction: Cu+2 + 2e- Cu0

Oxidation: 2 Br-1 Br20 + 2 e-

Br-

Br-

H2O

H2O

H2O

H2OH2O


- Battery +e-

H2O(ℓ)

e-

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H20

O20

AnodeCathode

+-

2 H2O 2 H2 + O2

Reduction: 4 H+1 + 4e- 2 H20

Oxidation: 2 O-2 O20 + 4 e-

H20

O-2

O-2

H+1

H+1H+1

H+1



The Electrolytic Cell

Documents

negative electrode

rightleftthe electrolytic

1nacl200the electrolytic

athe electrode

1kbr200 e

bthe positive electrode

e2na1 na0

e2k1 k0