Everything Science Grade 12

CHAPTER 5. THE CHEMICAL INDUSTRY 5.5

• The membrane cell is very similar to the diaphragm cell, except that the anode
  and cathode compartments are separated by an ion-selective membrane rather
  than by a diaphragm. Brine is only pumped intothe anode compartment. Positive
  sodium ions pass through the membrane into the cathode compartment, which
  contains water. As withthe other two cells, chlorine gas is produced at the anode
  and sodium hydroxide at the cathode.


• One use of sodium hydroxide is in the production of soaps and detergents, and
  so this is another important part of the chloralkali industry.


• To make soap, sodiumhydroxide or potassiumhydroxide react with a fat or an
  oil. In the reaction, thesodium or potassium ions replace the alcohol in the fat
  or oil. The product, a sodium or potassium salt of a fatty acid, is what soap is
  made of.


• The fatty acids in soap have a hydrophilic and a hydrophobic part in each
  molecule, and this helps to loosen dirt and clean items.


• Detergents are also cleaning products, but are made upof a mixture of com-
  pounds. They may alsohave other componentsadded to them to give certain
  characteristics. Some ofthese additives may be abrasives, oxidants or enzymes.


• The fertiliser industry is another important chemical industry.


• All plants need certain macronutrients (e.g. carbon, hydrogen, oxygen, potas-
  sium, nitrogen and phosphorus) and micronutrients (e.g. iron, chlorine, copper
  and zinc) in order to survive. Fertilisers providethese nutrients.


• In plants, most nutrients are obtained from theatmosphere or from thesoil.


• Animals also need similar nutrients, but they obtain most of these directly from
  plants or plant products. They may also obtainthem from other animals, which
  may have fed on plantsduring their life.


• The fertiliser industry is very important in ensuring that plants and crops receive
  the correct nutrients in the correct quantities toensure maximum growth.


• Nitrogen fertilisers can be produced industrially using a numberof chemical
  processes: The Haber process reacts nitrogen and hydrogen to produce ammo-
  nia; the Ostwald process reacts oxygen and ammonia to produce nitric acid;
  the nitrophosphate process reacts nitric acid withphosphate rock to produce
  compound fertilisers.


• Phosphate fertilisers are also produced through a series of reactions.The contact
  process produces sulfuric acid. Sulfuric acid then reacts with phosphate rock
  to produce phosphoric acid, after which phosphoric acid reacts with ground
  phosphate rock to produce fertilisers such as triple superphosphate.


• Potassium is obtainedfrom potash.


• Fertilisers can have a damaging effect on the environment when they are present
  in high quantities in ecosystems. They can leadto eutrophication. A number of
  preventative actions canbe taken to reduce theseimpacts.


• Another important part of the chemical industry is the production of batteries.


• A battery is a device that changes chemical energy into electrical energy.