Chemistry Paper One // Combined

• Energy is required to change from a solid to a liquid or liquid to a gas, energy is released when changing from a gas to a liquid or liquid to a solid
• If a reaction produces a solid or gas from liquids, it will appear cloudy or produce bubbles/fizzing
• Ionic bonding


  Transfer of electrons from a metal to a non-metal
• Covalent bonding


  Sharing of electrons between two non-metals
• For ionic compounds, the structure is a giant ionic lattice with high melting/boiling points and only conducts when molten or dissolved
• For simple covalent compounds, the structure is very small with low melting/boiling points, generally gases or liquids at room temperature, and do not conduct electricity
• For giant covalent compounds like diamond and graphite, the structure is a giant covalent lattice with high melting/boiling points and do not conduct or dissolve
• Diamond


  • Made of pure carbon with each carbon bonded to 4 others, incredibly hard and rare
• Measuring reactants and products

  Can be done by collecting the product in a gas syringe or using a scale/balance to measure mass changes
• Concentration


  Measured in moles per decimeter cubed, calculated as amount (moles) divided by volume (decimeter cubed)
• Balancing a reaction between hydrochloric acid and magnesium

  Hydrochloric acid (HCl) + Magnesium (Mg) → Magnesium chloride (MgCl2) + Hydrogen (H2)
• Concentration


  mass / volume
• Balancing an equation


  1. Recall the formula of things

  2. Balance the equation
• Determining products and formulas of salts

  1. Metal plus acid gives salts plus hydrogen

  2. Hydrogen is H2

  3. Magnesium chloride is MgCl2 (magnesium is 2+ ion, chlorine is 1- ion)
• Relative atomic mass (Mr)


  The larger number of the two atomic masses
• Metals above carbon in reactivity series

  • Require electrolysis to extract
  • Metals below carbon can be extracted by reduction
• Most metals are found as metal oxides
• If the metal in electrolysis is less reactive than hydrogen


  Something else is produced as gas
• Oxidation


  Loss of electrons
• Anode


  Positive electrode
• Cathode

  Negative electrode
• Balancing half-equations in electrolysis

  1. Balance elements first

  2. Balance charges by adding electrons
• Reactions of acids with metals

  • Acid + metal -> salt + hydrogen
  • Acid + metal oxide -> salt + water
  • Acid + metal hydroxide -> salt + water
  • Acid + metal carbonate -> salt + water + carbon dioxide
• Making pure copper sulfate

  1. Heat sulfuric acid, stir in copper oxide until in excess

  2. Filter to remove excess copper oxide

  3. Evaporate water to leave copper sulfate crystals
• Strong acids


  Fully dissociate into ions (HCl, HNO3, H2SO4, HBr, HI, HClO3)
• Weak acids


  Only partially dissociate into ions
• Ionic compounds must be molten or dissolved to conduct electricity
• Acid particles


  At high concentration, there are lots of acid particles per few water particles. At low concentration, there are few acid molecules per water molecule.
• Ionic compounds


  Have to be molten or dissolved to conduct electricity. In solid state, ions are fixed and cannot move to conduct electricity.
• Calculating energy change of a reaction

  1. Write balanced equation

  2. List bonds broken and formed

  3. Multiply bond energies

  4. Subtract energy of products from energy of reactants
• Burning hydrogen in oxygen to form water is an exothermic reaction with an energy change of -486 kJ/mol
• Transition metals


  • Hard, shiny, good conductors, can be used in jewelry, wires, saucepans, stained glass, statues
  • Compounds are often coloured (e.g. copper - blue/green, iron 2+ - light green, iron 3+ - orange/brown, cobalt - blue)