Chemistry

• Soluble salts

  • Nitrate
  • Chloride (except Ag, Pb)
  • Group 1 carbonates
• Insoluble salts

  • Sulfate (except Ba, Ca, Pb)
  • Chloride (Ag, Pb)
  • Rest of carbonates
• Solubility table

  Helps know whether a salt is soluble or not
• This solubility table is a 'secret' contributed by Ms Aida (BtVSS, MOE Singapore)
• Cation test with NaOH

  • Cu2+
  • Fe2+
  • Fe3+
  • Ca2+
  • NH4+
  • Zn2+
  • Al3+
  • Pb2+
• Cation test with NH3

  • Cu2+
  • Fe2+
  • Fe3+
  • Zn2+
  • Al3+
  • Pb2+
• Cation test table

  Shows colour changes when salts are added to NaOH or NH3
• Anion tests

  • Chloride (AgNO3 - white ppt)
  • Carbonate (CO2 - turns limewater chalky)
  • Sulfate (Ba(NO3)2 - white ppt)
  • Nitrate (Al, NaOH - turns red litmus blue)
  • Iodide (Pb(NO3)2 - yellow ppt)
• Gas tests

  • Ammonia (damp litmus paper turns blue)
  • Carbon dioxide (limewater turns chalky)
  • Chlorine (damp blue litmus paper bleaches)
  • Hydrogen (burning splint makes 'pop' sound)
  • Oxygen (glowing splint glows brighter/bursts into flame)
  • Sulfur dioxide (K2Cr2O7 turns green)
• Mole concept formulas

  • Mass of sample
  • Volume of gas
  • Number of moles
  • Number of particles
• All acids change blue litmus red
• Acids react with metals above hydrogen in reactivity series
• Acids react with bases to form salt and water
• Uses of ammonia

  • Manufacture of nitric acid
  • Produce fertilisers
• Hydrogen can be used as a fuel
• Ethene (alkene) is used to make plastic
• Potassium dichromate (VI)

  • Acts as an oxidising agent
  • Turns from orange to green when oxidised
• Potassium iodide

  • Acts as a reducing agent
  • Turns from colourless to brown when reduced
• Uses of ethanol

  • Solvent for organic compounds
  • To make alcoholic drinks
• Something with more carbon content is stronger
• Fermentation

  • Requires 37°C, enzymes, no oxygen
• Alkene addition of steam to become alcohol

  • Requires phosphoric acid catalyst, 300°C, high temperature/pressure
• Alkene addition of hydrogen to become alkane

  • Requires nickel catalyst
• Fractional distillation of petroleum

  Crude oil boiled, lighter fractions separate at lower boiling points, heavier fractions separate at higher boiling points, fractions collected at different boiling points
• Electrical conductivity

  Requires moving ions
• Heat conductivity

  Requires free moving electrons
• Boiling point

  Depends on strength of electrostatic attraction
• Why ionic compounds have high boiling point

  Consist of ions held by strong electrostatic attraction, large energy needed to break bonds
• Why covalent compounds have low boiling point

  Consist of molecules with weak intermolecular forces, small energy needed to break bonds
• Why ionic compounds conduct in molten/aqueous state

  Ions become free to move and convey charge
• Why ionic compounds cannot conduct in solid state

  Ions are fixed rigidly by strong electrostatic attraction and cannot move
• Why attaching magnesium to iron pipes increases their working life

  Magnesium is more reactive than iron, so water reacts with magnesium instead, reducing iron rusting (sacrificial protection)
• Why copper cannot be used instead of magnesium for sacrificial protection

  Copper is less reactive than iron, so iron would rust faster with copper attached
• Why hydrogen is more reactive than helium

  Hydrogen has 1 valence electron and can gain 1 more to become stable, helium has 2 valence electrons and is very stable
• Physical properties of metals

  • Good conductors of heat and electricity
  • High boiling and melting points
  • Malleable and ductile
• Why copper is recycled

  Copper is expensive and not as abundant as some other metals
• When naming an ester, you need to consider the structure
• Magnesium

  Above iron in the reactivity series
• Sacrificial protection

  1. Water reacts with Magnesium instead of iron

  2. Magnesium gets worn out

  3. Iron rusting is much reduced
• Copper is below iron in the reactivity series