1. Industrial chemistry Sodium Hydroxide (Lye, caustic soda) NaOH

6. Structural properties

7. Manufacture The major method for producing sodium hydroxide is electrolysis of concentrated brine (sodium chloride solution) produces chloride gas, hydrogen gas and sodium hydroxide. 2NaCl (aq) + 2H 2 O (l) -----> H 2(g) + Cl 2(g) + 2NaOH (aq) At the anode (positive electrode), the chloride ions (Cl - ) are oxidised to chloride gas (Cl 2(g) ). At the cathode (negative electrode), the sodium ions (Na + ) and water (H 2 O (l) ) are reduced to hydrogen gas (H 2(g) ) and sodium hydroxide (NaOH (aq) ).

8. The mercury cell process (Castner-Kellner) At the anode, titanium is the metal and chloride ions are oxidised to chloride gas: 2Cl - (aq) -----> Cl 2(g) + 2e - At the cathode, mercury is flowing along the bottom of the cell. Sodium ions are reduced to sodium metal: Na + (aq) + e - -----> Na (s) An amalgam is formed when sodium metal dissolves in the liquid mercury and it is removed to the decomposer. The amalgam then reacts with water to form sodium hydroxide, hydrogen gas and mercury: 2Na/Hg(l) + 2H 2 O (l) -----> 2NaOH(aq) + H 2(g) + 2Hg (l)

9. Nelson diaphragm cell process The saturated brine flows through the diaphragm and into the cathode compartment. At the anode, carbon or titanium coated with Ru-Ti, the chlorine ions are oxidized. At the cathode, steel mesh, hydrogen gas and hydroxide are produced: 2H 2 O (l) + 2e -----> H 2(g) + 2OH - (aq) The diaphragm allows the sodium ions to migrate across it and to combine with hydroxide, forming sodium hydroxide: 2H 2 O (l) + 2Cl - (aq) + 2Na + (aq) -----> 2NaOH (aq) + H 2(g) + Cl 2(g) Solid sodium hydroxide can be crystallised out.

10. Membrane cell process At the anode, titanium is the metal. At the cathode the metal is nickel and water is reduced: 2H 2 O (l) + 2e -----> H 2(g) + 2OH - (aq) Sodium ions migrate across the membrane and combine with hydroxide to form sodium hydroxide in the cathode compartment: 2H 2 O (l) + 2Cl - (aq) + 2Na + (aq) -----> 2NaOH (aq) + H 2(g) + Cl 2(g)

11. Soap making: The common fats, triglyceride esters react with sodium hydroxide to form glycerol and the sodium salt of the fatty acid which is soap. The equation can be simplified to: C 18 H 36 O 2 + NaOH -> alcohol + salt of the carboxylic acid (soap) The reaction between a strong base and a fat is called ‘saponification’, can be presented by the equation