Chemistry exam Paper 1 answers

• Group 1

  • Lower melting and boiling point
  • Lower density
  • Less strong
  • Softer
• Metals


  Conduct electricity because they contain delocalised electrons which carry charge through the structure
• When a metal and a non-metal react

  The metal atom loses electrons and the non-metal atom gains electrons
• In a reaction profile, the level of products is below the level of reactants
• Diamond

  • Has covalent bonds and four bonds per carbon atom
  • Is a macromolecule with atoms arranged in a giant lattice
• High melting point of diamond


  Due to strong covalent bonds which must be broken, requiring a lot of energy
• Fullerenes

  • Hollow, unreactive, not toxic, have a large surface area to volume ratio
• To obtain crystals, heat the solution until the crystallisation point is reached then leave the solution to cool and crystallise
• In an aqueous solution, there will always be hydrogen and hydroxide ions present
• The higher the concentration of an acid


  The lower the pH
• Aluminium is more expensive than carbon because more energy is needed to obtain aluminium from aluminium oxide by electrolysis
• Graphite


  Good electrical conductor because it has three covalent bonds per carbon atom, with one electron per carbon atom delocalised
• Graphite


  Soft and slippery due to its layered structure with weak intermolecular forces between layers, allowing the layers to slide over each other
• Isotopes


  Atoms with the same number of protons but different numbers of neutrons
• Mendeleev's periodic table became accepted because elements were discovered which fitted in the gaps he had left, and he predicted their properties correctly
• As you go down Group 1

  Reactivity increases
• Sodium Oxide


  Has a high melting point due to its giant structure with strong electrostatic forces of attraction between oppositely charged ions, requiring large amounts of energy to break the bonds
• Alloys


  Harder than pure metals because the atoms are different sizes, distorting the layers so they slide over each other less easily
• Electrolysis


  Uses electricity to produce a chemical reaction, while chemical cells use a chemical reaction to produce electricity
• Reactions with a high atom economy are used in industry for sustainable development, reducing waste, economic reasons, and to produce a high percentage of useful product
• Electrolysis


  Positive ions move to the negative electrode and negative ions move to the positive electrode, where they gain or lose electrons to form atoms
• Cryolite is added to the electrolyte in aluminium production to reduce the melting point and reduce the amount of energy needed, lowering the cost
• The carbon anodes in aluminium production have to be replaced regularly because the oxygen produced at the anode reacts with the carbon at high temperatures to produce carbon dioxide
• Electrolysis of aqueous solutions


  1. At the cathode, hydrogen is produced if the metal is above hydrogen in the reactivity series, otherwise the metal itself is produced

  2. At the anode, oxygen is produced unless there is a halogen present, in which case the halogen is produced instead
• Bohr model


  Proposes electrons orbit the nucleus in evenly spaced shells at specific distances from the nucleus
• When Mendeleev published his periodic table, protons and neutrons had not yet been discovered
• Activation energy


  The minimum energy needed for particles to reach before a reaction can occur
• Hydrogen fuel cells


  • Have no toxic chemicals, can refuel quickly, and can travel for a long time before needing to be refuelled
• Hydrogen fuel cell reactions


  1. At the anode: 2H₂ → 4H⁺ + 4e⁻

  2. At the cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O
• Limitations of simple particle models: does not show forces between particles, does not show speed and movement of particles, is only two-dimensional
• To reduce the volume of a gas


  Increase the pressure, cool it, or absorb it in a solid or condense it
• In halogens, the boiling point increases as you go down the group


  Because the size of the molecule increases, so the intermolecular forces increase in strength, requiring more energy to overcome them
• Melting and boiling points are bulk properties
• If an experiment produces a harmful gas, it should be done in a fume cupboard
• As you go down Group 7

  Reactivity decreases
• Burettes


  Can add substances in small, accurate increments, and measure variable volumes more accurately than a measuring cylinder
• Atomic weight


  The modern name is relative atomic mass
• In the periodic table, elements are arranged in order of atomic number
• In the alpha particle scattering experiment, most particles passed straight through, showing the mass of the atom is concentrated in the centre in the nucleus, with most of the atom being empty space, but some alpha particles were deflected, showing the atom has a positively charged nucleus
• Simple molecular substances


  Have a low boiling point due to weak intermolecular forces, requiring little energy to overcome them