Chemistry Topic 5

Chemistry Topic 5

1. Silicates

   • Aluminosilicates
     • Silicate structures with an Al atom replacing some Si atoms
       • This creates a negative charge, therefore a positive ion (usually K, Na, Ca or Al) is used to balance out the molecule
   • Questions usually involve using oxidation numbers to find ion ion charge
     • Silicon's oxidation number is 4
   • All are tetrahedral in shape
     • One silicon atom surrounded by 4 oxygen ions
   • Soil Silicates
     • Formed through the weathering of rocks.
     • Made up of aluminosilicate sheets, forming layers

2. Polymers

   • Large chains of hydrocarbon molecules made up of repeating units
     • Repeating units are called monomers
   • Have functional groups that determine the name of/the reactivity of the polymer
     • Eg: Hydroxyl (alcohol), ester, carboxylic acid, -anoate ion, amine, amide.
       • Hydolysis and condensation reactions either create or break ester links
         • Hydrolysis = add water (breaks ester)
         • Condensation = makes water (creates ester)
       • Polyamides are made from the condensation reaction between monomers with carboxylic acid and amine functional groups
   • Addition and Condensation polymers are 2 types
     • Addition = When monomers with C=C are 'added' together. Double bonds break, adding monomers together
     • Condensation = When monomers with two functional groups undergo a condensation reaction
   • 3 types of Bonding between ploymers
     • Dispersion forces = makes polymers soft, non-elastic, recyclable, re-shapable
     • Hydrogen Bonding = Strength, rigidity, elasticty
     • Cross-linking = more cross-linking = better strength, rigidity, hardness
   • Two types: Thermoplastic and Thermosets
     • Thermoplastics = Soft/pliable when heated, rigid when cooled. Reversible physical change. Only rely on secondary interactions. Recylable.
     • Thermosets = Don't soften/change shape when heated. Not recyclable. Heavily cross-linked. Must be shaped during polymerisation because it cannot be reversed. If a thermoset is heated too much, the covalent bonds break and charring occurs (carbon appears)

3. Soaps/Cleaning Agents

   • Soaps
     • Problem: Reacts with Ca and Mg ions to form scum. Scum is insoluble in water and creates blockages.
   • Detergents
     • Do not create scum