Electrolysis

What is electrolysis?• Electrolysis means

• “breaking up a compound with electricity”

• From the Greek• Electro – electricity• Lysis – breaking up

• Electrolysis keywords

• Anode – positive electrode• Cathode – negative electrode• Ion - charged particle• Electrolyte – substance that can be electrolysed

• Anion – ion that goes to the anode• Cation – ion that goes to the cathode

What is electrolysis?

• Electrolysis only works on substances made of ions.

• These are mostly the compounds of metals.

• The products of electrolysis are vital for our industry.

What is electrolysis?• Electrolysis will only

work if the ions in the substances are free to move.

• In solids the ions are fixed in place, so electrolysis will not work on solids

• But

• Electrolysis works on liquids and molten compounds

• Electrolysis works on solutions.

Melting

When ionic crystals melt

the ions are free to move

Dissolving

When an ionic substance dissolves

the ions spread out and are free to move

1

Electrodes NegativeCathode

PositiveAnode

D.C.current

Sodium ChlorideSolution

+ -

A little revision

Name the following

23 4

5

When Salt Dissolves

• The sodium ions and the chloride ions split up.

• This gives us• Na+ ions• and• Cl- ions

• Some water molecules also split up

• This gives us• H+ ions• and• OH- ions

NegativeCathode

PositiveAnode

D.C.current

+ -

Na+

Na+Cl-

Cl-H+

H+

OH-

OH-

Where will the ions go?

NegativeCathode

PositiveAnode

D.C.current

+ -

Na+

Na+Cl-

Cl-H+

H+

OH-

OH-

At the anode

Cl2There are lots of chloride ions in brine.They are attracted to the anode first

The chloride ions lose electrons and become chlorine gas

2Cl- Cl2 + 2e-

OXIDATION

The hydroxide ions get left behind in solution. There aren’t enough to discharge.

2e-

NegativeCathode

PositiveAnode

D.C.current

+ -

Na+

Na+Cl-

Cl-H+

H+

OH-

OH-

At the cathode2e-

The electrons get pumped into the cathode.

Positive ions are attracted to it.

Hydrogen ions get to the cathode before the sodium ions.

Hydrogen gas is discharged.

2H+ + 2e- H2Reduction

Sodium ions are left behind in solution.

H2

NegativeCathode

PositiveAnode

D.C.current

+ -

Na+

Na+Cl-

Cl-H+

H+

OH-

OH-

Where will the ions go?

H2Cl22e-

Products

• The three main products are:

• Hydrogen gas

• Chlorine gas

• Sodium hydroxide solution

Cl2

H2

Na+ OH-

NegativeCathode

PositiveAnode

D.C.current

+ -

Na+

Na+Cl-

Cl-H+

H+

OH-

OH-

In the Diaphragm Cell

H2Cl22e-

Cl-

Cl-Cl2