The document provides an overview of sodium hydroxide (NaOH), including its chemical properties, production methods via electrolysis of brine, and various applications such as household cleaners and industrial processes. It describes three electrolytic cells used for its production: the Castner-Kellner cell, Nelson diaphragm cell, and membrane cell, detailing their operations and advantages. Additionally, the document highlights the toxicity of chlorine gas and the environmental impact of certain production methods.

1. Manufacturing of
Sodium Hydroxide

2. Sodium Hydroxide
-Chemical name : sodium hydroxide
-Chemical formula : NaOH
- With Mwt. 39.99 g/mol
-Commercial name : caustic soda , Lye
“It is a white solid substance which dissolves
readily in water, its solution has soapy feeling
and corrosive to skin.”
-Commonly used as a Base
- Raw Material used in manufacturing:
Rock salt “NaCl” sodium chloride & water “H2O”

3. Production by Electrolysis
Electrolysis of concentrated NaCl solutions (brine)
produces chlorine gas, hydrogen gas and aqueous
sodium hydroxide.
2NaCl(aq) + 2H2O(l)  H2(g) + Cl2(g) + 2NaOH(aq)
- Uses of NaOH :
-domestic oven and drain cleaner
-pulp and paper production
-manufacture of rayon and
other synthetic fibres
-soap and detergent production
-removal of sulfur dioxide and
hydrogen sulfide in petroleum refining

4.  Uses of Cl2 Gas:
- treat drinking water and swimming pool
water by killing bacteria in .
- 20% of chlorine produced
is used to make PVC
- used in organic chemistry processes-for
example; as an oxidizing agent and a
substitution for hydrogen
- make chloroform (an anesthetic) and
carbon tetrachloride (a dry-cleaning
solvent).
 Chlorine gas is itself very poisonous, and
was used as a chemical weapon during
the First World War.
Dangerous

5. Types of electrolytic cell
There are three types of electrolytic cell
are used to produce sodium hydroxide
from brine:
Castner-Kellner Cell (Mercury
Process)
Nelson Diaphragm Cell
Membrane Cell

6. Castner-Kellner Cell (Mercury
Process)-Anode (+ve electrode): titanium
*Anode reaction (oxidation):
2Cl-
(aq)  Cl2(g) + 2e
-Cathode (-ve electrode):
mercury flowing along bottom of cell
*Cathode reaction (reduction):
Na+
(aq) + e  Na(s)
-Na(s) dissolves in the liquid mercury
to form an amalgam which is removed
to the decomposer.
-In the decomposer the amalgam
reacts with water to form sodium
hydroxide, hydrogen gas and mercury.
2Na/Hg + 2H2O(l)  2NaOH(aq) + H2(g) + 2Hg(l)
Sodium hydroxide solution and hydrogen gas are collected.
Mercury is recycled through the electrolytic cell
-Mercury is toxic so care must be taken to prevent mercury losses.

7. Nelson Diaphragm Cell
 Porous diaphragm of asbestos or metal oxide with polymer separates anode and
cathode compartments.
 Diaphragm prevents hydroxide ions entering anode compartment and prevents
chloride ions entering cathode compartment.
 Saturated brine enters anode compartment
where chlorine gas is produced.
 Anode (+ve electrode):
carbon (graphite) or titanium
coated with Ru-Ti oxide.
Anode reaction (oxidation):
2Cl-
(aq)Cl2(g) + 2e
 Cathode (-ve electrode):
steel mesh
Cathode reaction (reduction):
2H2O(l) + 2e  H2(g) + 2OH-
(aq)
 Na+ migrates across diaphragm to cathode
compartment combining with OH-to form NaOH.
 Overall cell reaction (showing Na+ spectator ions):
2H2O(l) + 2Cl-
(aq) + 2Na+
(aq)  2NaOH(aq) + H2(g) + Cl2(g)
 Product contains sodium chloride and sodium hydroxide. NaOH(s) can be crystallised
out.

8. Membrane Cell
 Favored method for producing very pure NaOH with no hazardous
waste, and with lowest energy requirements.
 Ion-exchange membrane selectively allows Na+ and water to flow to
the cathode compartment but prevents products from moving
between compartments.
 Saturated brine enters the anode
compartment where chlorine gas is formed.
 Anode (+ve electrode): titanium
 Anode reaction (oxidation):
2Cl-
(aq)  Cl2(g) + 2e
 Cathode (-ve electrode):nickel
 Cathode reaction (reduction):
2H2O(l) + 2e  H2(g) + 2OH-
(aq)
 Na+ migrates across the membrane to
cathode compartment combining with OH- to form NaOH.
 Overall cell reaction (showing Na+ spectator ions):
2H2O(l) + 2Cl-
(aq) + 2Na+
(aq)  2NaOH(aq) + H2(g) + Cl2(g)
 Product is concentrated sodium hydroxide.

9.  Process Advantages:
- Very Pure NaOH.
- No hazardous waste.
- Need lowest energy.
MEMBRANE CELL
CASTNER-KELLNER CELL
 Amalgam is mercury alloy “Hg& metal”
All most all metals can form amalgam with Hg,
exception : Iron, Platinum, Tungsten and
Tantalum.
 Process Advantages :
- Process very efficient.
- Produce very pure NaOH.
 Process Disadvantages :
- High electricity consumption .
- Environmental pollution due to escape of
mercury vapors .

10. References :
 AUS-e-TUTE is a science education
website
http://www.ausetute.com.au/
 Business Science Articles website
http://www.business-science-articles.com/
 Periodic Table website
http://www.rsc.org/periodic-table
 Look Chem “Look for chemicals”
website
http://www.lookchem.com/