Chemistry paper 1

• OIL RIG


  Oxidation Is Loss (of electrons)

  Reduction Is Gain (of electrons)
• Element


  All of the atoms are the same
• Compound


  Contain two or more different elements chemically combined in a fixed proportion
• Mixture


  Different elements or compounds not chemically combined together
• Molecule


  Any elements chemically joned
• Filteration


  Used to separate an insoluble solid from a liquid
• Crystalisation


  Used to separate a soluble solid from a liquid
• Simple distillation


  Used to separate a liquid from a sold if we want to keep the liquid
• Fractional distillation


  Separate a mixture of different liquids
• History of an atom

  Ancient Greek - everything made of atoms

  189Neutrons7-Plum pudding

  Alpha scattering Experiment - Fired alpha particles through a sheet of gold - Nuclear Model

  Bohr - electrons at specific levels

  Chadwick -
• Radius of atom


  0.1nm
• Radius of nucleus


  1*10-14
• Isotopes


  Atoms of an element with different numbers of neutrons
• Ions


  Atoms which have an overall charge. They have gained or lost electrons.

  Positive ions have lost electrons.

  Negative ions have gained electron.
• Energy Levels


  Electrons are held in the rings around the nucleus. Each energy level can hold a certain amount of electrons. 2,8,8,18
• Relative atomic mass


  Average of the mass numbers of the different isotopes. Weighted by abundance.
• Relative atomic mass =

  (mass of isotope 1percentage abundance of isotope 1) + (mass of isotope 2percentage abundance of isotope 2) / 100
• History of Periodic table

  - Dobereiner's Triads

  - Newland's octaves

  - Mendeleev's table- sorted by atomic mass, gaps left for missing elements
• Metal ions


  Outer electrons lost to form a positive ion
• Group 0


  Noble gases:

  - Very unreactive

  - Going down increase the boiling point
• Group 1


  Alkali metals:

  - Soft and very reactive

  - React rapidly with oxygen to form metal oxides

  - More reactive down the group

  - React rapidly with chlorine to form metal chloride

  - React with water to make metal hydroxide and hydrogen (universal indicator purple + effervescence )
• Group 7


  Halogens:

  -Form molecules with two atoms joined covently

  - Melting and boiling points increase down the group

  - Form covelant compounds with non metals and ionic compounds with metals

  - Form - ions ending ide

  - Less reactive as you go down

  - A more reactive halogen will displace a less reactive one from an aqueous solution of its salt
• Transition Metals


  - Hard and strong

  - High melting points

  - High density

  - Less reactive

  - Form ions with different charges

  - Form coloured compounds

  - Can be used as catalysts
• Acids


  Produce hydrogen ions in aqueous solutions

  e.g Hydrochloric acid (HCL), Sulfuric acid (H2SO4), Nitric acid (HNO3)
• Bases


  Chemicals which can nuetralise acids and produce a salt in water

  - Normaly oxides or hydroxides
• Alkalis


  Bases that are soluble in water
• PH scale


  Tells us weather a solution is acidic or alkaline. You can use a pH probe (electrical) or universal indicator (1-14, acid-alkaline, red-blue)
• Acid Reactions


  Acid + Metal -> Salt + Hydrogen

  Acid + Base -> Salt + Water

  Acid + Metal Carbonate -> Salt + Water + Carbon Dioxide
• Practical: Making soluble salts

  1. Fixed amount of sulfuric acid (limiting)

  2. Gently heat until almost boiling

  3. Use a spatula to add small amounts of copper oxide to the acid

  4. Stir the solution using a glass rod

  5. The copper oxide appear to disappear

  6. Add copper oxide until some powder remains after stirring

  7. Filter to remove unreacted copper oxide

  8. Place solution in evaporating basin and gently heat using a water bath

  9. leave solution until crystals form
• Strong acids


  Fully ionise in aqueous solutions. Strong acids have a lower pH (pH measures concentration)
• Concentration of acids


  Tells the amount of acid molecules in a given volume of solution
• Practical: Titration


  1. Use a pipette to transfer 25cm3 of sodium hydroxide solution in a conical flask

  2. Add 5 drops of Methyl Orange

  3. Put flask on white tile

  4. Fill a burette with sulfuric acid

  5. Add acid till the solution is neutral

  6. Once we get near to colour change add drop by drop, make sure to swirl solution

  7. Read the volume
• concentration =


  number of moles / volume
• Ionic Compounds


  -cannot conduct electricity

  -when they are melted or dissolved in water they become electrolytes and the ions are free to move
• Electrolysis of Aluminium oxide

  -Aluminium oxide is melted with cryolite to lower boiling point and therefore save money

  -electrodes made of graphite

  -Anode must be replaced regularly as oxygen reacts with it

  -Lots of energy needed
• Electrolysis of Aluminium oxide: Half Equasions

  Cathode:

  Al3+ + 3e- -> Al (reduction)

  O2 -> O + 2e- (oxidation)
• Electrolysis of water


  - Hydrogen is produced at the cathode if the metal is more reactive than hydrogen

  - Oxygen is made at anode
• Exothermic reactions


  Transfer energy from the reacting molecules to the surroundings. The surroundings get hotter. e.g.combustion neutralisation, handwarmers

  
• Endothermic reactions


  Take energy from the surroundings, they got colder. e.g. thermal decomposition

  
• Activation energy


  The minimum amount of energy the particles must have in order to successfully collide and react.