Electrolysis Industrial Uses Electrode Products

8/3/2019 Electrolysis Industrial Uses Electrode Products

1/23

ELECTROLYSIS

Module C2

Splitting up ionic compounds (F)

Molten compounds

Ionic solutions & discharge rules

Q = It and OILRIG

Brine and purifying copper

+

-

+

-+

-+

-

+-+

-+ +

-


2/23

Cl- ION

Na+

ION

SPLITTING UP IONIC COMPOUNDS 1

Ionic compounds (eg sodium chloride) are made from:

POSTIVE IONS (atoms which LOST negative electrons)NEGATIVE IONS (atoms which GAINED negative electrons)

As these ions have OPPOSITE CHARGES they attract each

other strongly to form IONIC BONDS


3/23

SPLITTING UP IONIC COMPOUNDS 2

2 ways to split up the ions:

-+ +

- + --+ +

- + -

+

-

+

-+

-+

-

+-

+

-+ +

-

MELT

+ --

+

+--+

- +

DISSOLVE

H2O800C 20C


4/23

SEPARATING THE IONS 1

+_

Battery pulls

electrons off one

electrode and

pushes them

onto the other

Metal

ELECTRODEELECTRON

This IS SHORT OF

electrons so becomes

POSITIVELY CHARGED

ANODE

This HAS EXTRAelectrons so becomes

NEGATIVELY CHARGED

CATHODE


5/23

+

+ -

+- +

-

-

+

- -+ +

-

+

MOLTEN IONIC

COMPOUND

+ ANODE - CATHODE

When the battery is switched on,the + IONS move to the CATHODE

the IONS move to the + ANODE

SEPARATING THE IONS 2

This gives a way to SPLIT UP IONIC COMPOUNDS: ELECTROLYSIS


6/23

Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt)

+

Cl-

Cl

-

Cl-

Cl

-

ClCl

Cl Cl

- =chloride ION,

extra 1 electronCl- Cl

chlorine ATOM,

NEUTRALCl Cl Cl2

molecule

- chloride IONS

lose their extraelectrons and

turn into neutral

chlorine ATOMS

At ANODE: Cl- e- + Cl

then: Cl + Cl Cl2 (gas)

Both together:

2Cl- 2e- + Cl2


7/23

Na+


+

At CATHODE: Na+ + e- Na

Na+

Na+ Na+

Na

NaNa

Na

= sodium ION,missing1 electron

sodium ATOM,

NEUTRALNa++ Na

+ sodium IONS

gain an extra

electron and turn

into neutral

sodium ATOMS

molten sodium

metal sinks to

bottom


8/23


MOLTEN

SODIUM

CHLORIDE

+ ANODE - CATHODE

CHLORINE

gas Cl2

SODIUM

metal Na

At ANODE:

Cl- e- + Cl At CATHODE:Na+ + e- Na

Cl + Cl Cl2 (gas)

ELECTRONS

Cl- Na+


9/23

Example 2: Splitting up MOLTEN LEAD BROMIDE PbBr2

MOLTEN

LEAD

BROMIDE

+ ANODE - CATHODE

BROMINE

gas Br2

LEAD

Metal Pb

At ANODE:

Br- e- + Br At CATHODE:Pb2+ + 2e- PbBr + Br Br2 (gas)

ELECTRONS

Br- Pb2+

Both together:

2Br- 2e- + Br2


10/23

What happens when the ionic compounds are dissolved

in water?

Here, water molecules break up into HYDROGEN IONS, H+

and HYDROXIDE IONS OH-

H2O H+ + OH-So, in an ionic solution (eg sodium chloride solution), there will be

FOUR types of ion present:

TWO from the ionic compound and TWO from the water (H+ + OH-)

SODIUM CHLORIDE

SOLUTION NaCl (aq)

Cl-

Na+

OH- H+Na+

Cl-OH-H+

H+

OH- Cl-

Na+


11/23

IONIC SOLUTION

Cl-

Na+

OH- H+Na+

Cl-

OH-

H+

H+

OH- Cl- Na+

Which ions gain or lose electrons (get discharged)

and which stay in solution?


12/23

IONIC SOLUTIONS: At the CATHODE

+

At CATHODE: 2H+ + 2e- H2

sodium ION,

missing 1

electron

Hydrogen ATOM,

NEUTRALNa+ H

Na+

Na+

H+

H+

H

H

H+hydrogen ION,

missing 1

electron

As HYDROGEN is

LESS REACTIVE

than SODIUM, it is

discharged. The

sodium ions stay in

solution.

which

ions?


13/23

+

Cl-

Cl-

Cl-

Cl-

ClCl

Cl Cl

chloride ION,

extra 1 electronCl- Cl

chlorine ATOM,

NEUTRAL

At ANODE: 2Cl- 2e- + Cl2

IONIC SOLUTIONS: At the CATHODE halogen compounds

If the ion is a

HALOGEN (Cl, Br, I)it is discharged and

chlorine (or Br or I)

is given off and the

OH-

ions stay insolution

OH

O HOH

O H

O Hhydroxide ION,

from water

extra electron

which

ions?


14/23


15/23

+ ANODE

Attracts ions (Anions)

If ions are HALOGENS ie

chloride Cl-

bromide Br

-

iodide I-

the HALOGEN is produced.If ions are NOT HALOGENS

Eg sulphate SO42-

,

nitrate NO3-

carbonate CO32-

OXYGEN is produced.

- CATHODE

Attracts + ions (Cations)

If + ions (metals) are MORE

REACTIVE than hydrogen

K, Na, Ca, Mg, Zn, Fe

Then HYDROGEN is

produced

If + ions (metals) are LESS

REACTIVE than hydrogen

Cu, Ag, Au

Then the METAL is produced

RULES FOR IONIC SOLUTIONS


16/23

potassiumchloride

Compound State Anode(+)

Cathode(-)

Ions

molten K+Cl- potassium

chlorine

aluminiumoxide

molten Al3+O2- aluminium

oxygen

copperchloride solution Cu

2+

Cl

-

H

+

OH- copper chlorinesodiumbromide

solution Na+Br-

H+ OH-hydrogen

bromine

silver nitrate solution Ag+NO3- H+

OH-silver oxygen

potassiumchloride

solution K+Cl- H+

OH-hydrogen

chlorine

zinc sulphate solution Zn+SO42- H+

OH-

hydrog

en

oxygen

(REACTIVITY: K+ Na+ Ca2+ Mg2+ Al3+ Zn2+ Fe3+ H+Cu2+ Ag+ Au3+ )

(REACTIVITY: K+ Na+ Ca2+ Mg2+ Al3+ Zn2+ Fe3+ H+


17/23

ELECTROLYSIS makes a CIRCUIT

Complete electric circuit:

Current carried by:

ELECTRONS in electrodes/wires

IONS in the electrolyte

To DOUBLE the MASS of substance

discharged at electrodes:

2 x CURRENT (2x batt. voltage)2 x TIME current flows for

(Q = I t)

-

+

+-


18/23

Cl-

Cl-

Cl-

Cl- Na+ Na+

Na+ Na+

OILRIG

-ions LOSING electrons

to become atoms is calledOXIDATION

(even though oxygen may

not be involved)

+ ions GAINING electrons

to become atoms is calledREDUCTION

Oxidation is loss,

reduction is gain

OILRIG


19/23


20/23

INDUSTRIAL ELECTROLYSIS OF BRINE

ANODE

OH- and Cl-

2Cl- 2e- + Cl2

OH-

left in solutionso concentration

grows

CATHODE

H+ and Na+

2H+ + 2e- H2

Na+

left in solutionso concentration

grows

Chlorine gas Hydrogen gas

Sodiumchloridesolution(neutral)slowly

changed to

BRINE(NaCl solution)


21/23

Industrial chlorine production from electrolysis of

brine


22/23

IMPURE COPPER

ANODE

PURE COPPER

CATHODECopper sulphate

CuSO4 solution

PURIFYING COPPER

Cu2+

Cu

CuCu2+ Cu2+Copper atoms

from impure

copper areOXIDISED to

copper ions

Copper ions transported

from anode to cathode

Copper ions

from impure

copper are

REDUCED to

copper atoms

As the atoms of the impurities are not

transported, the copper that builds up on the

anode is extremely pure.


23/23

IMPURE

COPPER

ANODE

PURE

COPPER

CATHODE

IMPURE

COPPER

ANODE

PURE

COPPER

CATHODE

Over time, the impure anode dissolves away and the

impurities sink to the bottom. The pure cathode grows as

more pure copper is deposited on it.

Why will the concentration of the solution stay the same?

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Electrolysis Industrial Uses Electrode Products