exemplar questions

• Why is excess zinc oxide used rather than excess hydrochloric acid? (1)

  Excess zinc oxide can be filtered off
• Describe and explain how the surface of the early earth and its atmosphere has changed to form the earth we live on today (6)

  -oxygen increased (and carbon dioxide decreased) due to increased levels of photosynthesi, as plants and algae developed

  -oceans formed and dissolved carbon dioxide

  carbon dioxide became locked up in sedimentary/carbonate rocks

  -oceans formed because water vapour in the atmosphere condensed

  -nitrogen formed because ammonia in the earths early atmosphere reacted with oxygen

  -volcanoes reduced because the earth cooled, forming a crust
• Explain why chlorine is a gas at room temperature, but sodium chloride is a solid at room temperature (6)

  CHLORINE

  -covalent bonds between atoms

  -forming simple molecules

  -there are no intermolecular forces

  -therefore a low boiling point

  SODIUM CHLORIDE

  -ionic bonds

  strong electrostatic attraction in all directions, acting between oppositely charged ions

  -therefore forming a giant ionic lattice

  -due to this lots of energy needed to overcome forces, therefore high boiling + melting points
• Explain why the reactivity of elements increases going down group 1 but decreases going down group 7

  Group 1 elements need to lose one electron when they react.

  As you go down group one there are more energy shells so more distance between the outer electron and the nucleus

  This means the outer electron is less attracted to the nucleus going down group 1

  Therefore it is easier to lose the outer electron as you go down the group

  In group 7 the elements need to gain an electron so as the outer electrons are less attracted to the nucleus as you go down the group, it is harder to gain an electron
• Compare the chemical and physical properties of transition metals and group 1 electrons


  Physical

  Transition elements:

  High melting points

  High densities

  Strong

  Hard

  Group 1

  Low melting points

  Low densities

  Soft

  
  

  Chemical

  Transition elements

  Low reactivity

  Used as catalysts

  Ions with different charges

  Make coloured compounds

  Group 1

  very reactive

  Not used as catalysts

  Form white compounds
• Describe the structure and bonding in metals

  Some electrons from the outer shells are free to move through the structure. This holds the atoms together

  
  

  The atoms are in regular layers in a giant structure. They are closely packed together
• Describe, in terms of electrons, what happens when a magnesium atom react with a chlorine atom to produce magnesium chloride


  Magnesium loses two electrons and chlorine gains one electron

  One magnesium and two chlorines

  The electrons give the ions eight electrons in the outer shell
• "The more energy levels (shells) of electrons an atom has, the weaker the covalent bonds that it forms."

  Use the above statement to predict and explain how the overall energy change for the reaction of ethene with chlorine will differ from the overall energy change for the reaction

  Size and strength

  Chlorine atoms have fewer elec
• Explain, in terms of particles, how and why the rate of reaction changes during the reaction of calcium carbonate with hydrochloric acid.
• Magnesium oxide contains magnesium ions (Mg2+) and oxide ions (O2-).

  Describe, as fully as you can, what happens when magnesium atoms react with oxygen atoms to produce magnesium oxide.
• Explain why graphite can be used as the lead of pencils

  It is made of layers of carbon atoms

  With weak forces of attraction between layers

  This means layers can slide over each other and peel off
• Explain why graphite can be used as an electrical conductor

  There are electrons which are free to move and carry electrical charge

  As each carbon atom only has three covalent bonds
• Describe a method for making pure crystals of copper sulfato from copper carbonate and sulfúrico acid

  Put the sulfuric acid in a beaker and gently heat it

  Add copper carbonate one spatula at a time

  Until copper carbonate is in excess and no more effervescence occurs

  Filter excess copper carbonate using filter paper and funnel

  Pour solution into an evaporating basin

  Heat using a Bunsen burner

  Leave for half the water to evaporate

  Decant solution (evaporate)

  Pat dry
• Describe how copper chloride crystals could be made from a reaction of copper carbonate and hydrochloric acid

  Add excess copper carbonate

  Filter to remove excess copper carbonate

  Heat filtrate to evaporate off some water

  Leave to cool so crystals form
• "The more energy levels of electrons an atom has, the weaker the covalent bond that it forms" predict and explain the overall energy change for the reaction of ethene and chlorine compared with ethene and bromine

  Chlorine atoms have fewer electron energy levels

  Chlorine atoms have stronger bonds than bromine atoms

  
  

  More energy is required to break bonds with chlorine

  More energy is given out when making bonds with chlorine

  Overall energy change depends on the sized of the energy changes