ic s4 p1+2 – first hand investigation and analyse information from secondary sources to predict...

IC S4 P1+2 – First hand investigation and analyse

information from secondary sources to predict and

explain different products of aqueous and molten NaCl

Use this in conjunction with the worksheet!

Electrolysis of salt 3

• Na+ ions move to the cathode but do notdo not accept electrons.

• It is the hydrogen ions (from water) that gain electrons.

• As a result hydrogen gas is formed at the cathode.

RED CAT Cathode • H2O is more easily reduced than Na+

• H2O(l) + e- ½ H2(g) + OH-(aq)

• This means that H2(g) and OH- is formed at the negative cathode.

• Na+ is left behind.

Na+Cl-

HHO

HO-

H+


Cl22Cl- - + 2e- Chlorine gas is formed

At the ANODE.• Why do you think that

even though the reduction potentials predict that oxygen will be formed, we get chlorine?

• Standard Reduction Potentials (1M)


Cl22Cl- - + 2e- Chlorine gas is formed

AN OX Anode• Chloride and water

have similar reduction potentials.

• But the NaCl is 2M concentration and in this condition it has a lower potential than water and is more easily oxidised.

• 2Cl- Cl2 + 2e-


Na+Cl-

HO-

H+

Changed into chlorine gas at anode

Changed into hydrogen gas at cathode

No change “Spectator ion”

No change “Spectator ion”

• What happens to the various ions?


• Sodium hydroxide is what is left in the solution at the end of electrolysis

Na+Cl-

HO-

H+

Na+

HO-

Cl

Cl

H

H

Solution Electrodes

Electrolysis of salt

Complete Q1-7 on the worksheet.

What happens if we dilute the concentration of NaCl?

What happens if we dilute the concentration of NaCl?

RED CAT Cathode

• H2O is more easily reduced than Na+

• H2O + e- ½ H2+ OH-

• This means that H2(g) and OH- is formed at the negative cathode.

• Na+ is left behind.

What happens if we dilute the concentration of NaCl to 1.00 M?

AN OX Anode

Under Standard conditions H2O is more easily oxidised than Cl-

.

H2O + 2H+ + ½ O2 + 2e-

• This means that H+ and O2 is formed at the negative cathode.

Complete Q8 - 10.

What do you predict would happen if we could perform electrolysis on

molten NaCl?

Molten NaCl.Contains only Na+ and Cl- ions.

Anode (Oxidation)2Cl- (l) Cl2(g) + 2e-

Cathode (Reduction)Na+(l) + e- Na(l)

Uses of the products of electrolysis of NaCl(aq). (You do not need to

know all of this but it is interesting)

Electrolysis of salt - summary

Uses of chlorine 1

Sodiumchloride‘rock salt’solution

electrolysis

Chlorinegas Bleaching agent,

e.g. paper industry

Sterilisation of watere.g. swimming poolsand drinking water


electrolysis

Chlorinegas

Bleaching agent, e.g. paper industry

Sterilisation of watere.g. swimming poolsand drinking water

con

tin

ue

d

Manufacture of HCl

Manufacture of Cl-containing organic chemicals

Uses of chlorine 2

Manufacture of HCl Manufacture of PVC andother plastics

Uses of chlorine 3

Manufacture ofCl-containing organic chemicals

Pesticides

Solvents, e.g. solvent fortippex, & ‘dry cleaning’

dyes

Manufacture of HCl Manufacture of PVC andother plastics

Uses of chlorine 4

Uses of sodium hydroxide 1


electrolysis Sodiumhydroxide

Manufacture of soap

Manufacture of Paper

Extraction of aluminium


electrolysis Sodiumhydroxidesolution

Extraction ofaluminium

Manufacture of soap


Textiles (wool,cotton)



electrolysis Sodiumhydroxidesolution

Extraction ofaluminium

Manufacture of soap


Neutralisationof acid effluents

Textiles (wool,cotton)


Uses of Cl and NaOH

Join the appropriate substances with arrows.

Uses of products from salt

chlorinehydrogen

Sodium hydroxide

salt

Hydrochloric acid

pvc

soapbleach

Organic chlorides

Aluminium extraction

dyes

Acid neutralisation

Salt Water Purify

Why Purify?

Mg2+ +

Ca2+ +

SO42- +

Fe2+ +

Salt Water Purify

Why Purify?

Mg2+ + 2OH- Mg(OH)2

Ca2+ + CO32- CaCO3

SO42- + Ca2+ CaSO4

Fe2+ + 2OH- Fe(OH)2

Net ionic equation?

Ignore the spectator ion(s)

2H2O + 2Cl- Cl2 + H2 + 2OH-

Full equation?

Include the spectator ion(s)

Net ionic equation?

Ignore the spectator ion(s)

2H2O + 2Cl- Cl2 + H2 + 2OH-

Full equation?

Include the spectator ion(s)

2H2O + 2NaCl Cl2 + H2 + 2NaOH

Mercury Process Diaphragm Process Membrane Process

Mercury process actually produes Na at the cahode…

Na then reacts with water

2Na + H2O 2NaOH + H2

ic s4 p1+2 – first hand investigation and analyse information from secondary sources to predict...

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