1. 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!

2. Electrolysis of salt 3
Na+ ions move to the cathode but do not accept electrons.
It is the hydrogen ions (from water) that gain electrons.
As a result hydrogen gas is formed at the cathode.

4. H2O is more easily reduced than Na+ H2O(l) + e-  ½ H2(g) + OH-(aq)
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- H O- H+ H O

5. 2Cl- - + 2e- Cl2 Electrolysis of salt 1 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)
Chlorine gas is formed
2Cl e-
Cl2

7. 2Cl- - + 2e- Cl2 Electrolysis of salt 1 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-
Chlorine gas is formed
2Cl e-
Cl2

9. What happens to the various ions?
Electrolysis of salt 4
What happens to the various ions?
No change “Spectator ion”
Na+
Cl-
Changed into chlorine gas at anode H O-
Changed into hydrogen gas at cathode H+
No change “Spectator ion”

10. Electrolysis of salt 5
Sodium hydroxide is what is left in the solution at the end of electrolysis
Na+
Cl- H O- H+
Na+ H O- Cl H
Solution
Electrodes

11. Electrolysis of salt
A drag and drop activity

12. Complete Q1-7 on the worksheet.

13. What happens if we dilute the concentration of NaCl?

14. 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.

16. 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.

17. Complete Q

18. What do you predict would happen if we could perform electrolysis on molten NaCl?

19. Molten NaCl. Contains only Na+ and Cl- ions. Anode (Oxidation) 2Cl- (l)  Cl2(g) + 2e- Cathode (Reduction) Na+(l) + e-  Na(l)

20. Uses of the products of electrolysis of NaCl(aq)
Uses of the products of electrolysis of NaCl(aq). (You do not need to know all of this but it is interesting)

21. Electrolysis of salt - summary
A drag and drop activity

22. Uses of chlorine 1 Sterilisation of water e.g. swimming pools
and drinking water
Sodium
chloride
‘rock salt’
solution
electrolysis
Chlorine
gas
Bleaching agent,
e.g. paper industry

23. Uses of chlorine 2 Sterilisation of water e.g. swimming pools
and drinking water
Sodium
chloride
‘rock salt’
solution
electrolysis
Bleaching agent,
e.g. paper industry
Chlorine
gas
Manufacture of HCl
continued
Manufacture of
Cl-containing
organic chemicals

24. Uses of chlorine 3 Manufacture of PVC and Manufacture of HCl
other plastics
Manufacture of HCl

25. Uses of chlorine 4 Manufacture of PVC and Manufacture of HCl
other plastics
Manufacture of HCl
Pesticides
Manufacture of
Cl-containing
organic chemicals
Solvents, e.g. solvent for
tippex, & ‘dry cleaning’
dyes

26. Uses of sodium hydroxide 1
Extraction of aluminium
Sodium
chloride
‘rock salt’
solution
Manufacture of soap
electrolysis
Sodium
hydroxide
Manufacture of Paper

27. Uses of sodium hydroxide 2
Extraction of
aluminium
Sodium
chloride
‘rock salt’
solution
Manufacture of soap
Sodium
hydroxide
solution
electrolysis
Manufacture of Paper
Textiles (wool,
cotton)

28. Uses of sodium hydroxide 3
Extraction of
aluminium
Sodium
chloride
‘rock salt’
solution
Manufacture of soap
Sodium
hydroxide
solution
electrolysis
Manufacture of Paper
Textiles (wool,
cotton)
Neutralisation
of acid effluents

29. Uses of Cl and NaOH
A drag and drop activity

30. Uses of products from salt
Join the appropriate substances with arrows.
chlorine
hydrogen
Sodium hydroxide
salt
Hydrochloric acid
pvc
soap
bleach
Organic chlorides
Aluminium extraction
dyes
Acid neutralisation

31. Purify
Salt Water
Why Purify?
Mg2+ +
Ca2+ +
SO42- +
Fe2+ +

32. Purify
Salt Water
Why Purify?
Mg2+ + 2OH-  Mg(OH)2
Ca2+ + CO32-  CaCO3
SO42- + Ca2+  CaSO4
Fe2+ + 2OH-  Fe(OH)2

33. Net ionic equation?
Ignore the spectator ion(s)
2H2O + 2Cl-  Cl2 + H2 + 2OH-
Full equation?
Include the spectator ion(s)

34. 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

35. Mercury Process Diaphragm Process Membrane Process
Mercury process actually produes Na at the cahode…
Na then reacts with water
2Na + H2O  2NaOH + H2