model answers p1 chem

• Explain how lubricating the chain with oil prevents corrosion of the steel chain (2)

  • air/oxygen =excluded because oil acts as a barrier
  • air/oxygen and water/moisture both needed for iron to rust
• Explain why the exposed iron does not rust when iron fences are galvanised by coating them with a layer of zinc, even if the layer of zinc is scratched (2)

  • zinc corrodes easier than iron/ zinc rects wit air and water instead
  • zinc= more reactive than iron
• explain (in terms of their structure and bonding) why metals have high melting points

  • metal ions/ cations = surrounded by delocalised electrons
  • strong forces of attraction between delocalised electrons + metal ions/ cations
  • needs a lot of energy to overcome the forces of attraction
• Explain how the structure of a nickel atom, Ni (a metal) changes when it forms a nickel ion (2+)

  • loss of electrons
  • two electrons
• Describe how a sample of pure dry nickel sulfate crystals can be obtained from the mixture of nickel sulfate solution and excess solid nickel carbonate in the beaker

  nickel carbonate + sulfuric acid -> nickel sulfate + carbon dioxide + water

  • filter
  • crystallisation
  • heat solution (to concentrate)
  • allow to cool
  • dry crystals between filter papers
• explain why Aluminium has to be extracted from its oxide by electrolysis, and not heated by Carbon (2)

  • aluminium is high in reactivity
  • aluminium cannot be reduced by carbon
• describe how growing plants can result in the phytoextraction of copper

  • plants absorb copper ions from the soil
  • plants are harvested and burned to leave copper
• Predict the method that will have to be used to extract calcium from its ore

  electrolysis
• Give two reasons why percentage yield can be less than 100%

  • unwanted side reactions
  • practical losses during the experiment
  • incomplete reactions
• how can apparatus be improved to increase the amount of pure water collected from the same volume of sea water

  • use a condenser
  • to ensure all the water vapour condenses
• What type of bonds are present in diamond, graphene, and fullerene C60?

  Single covalent bonds
• How are carbon atoms bonded in diamond?

  Each carbon atom is joined to 4 others
• What type of structure do diamond and graphene have?

  Giant covalent lattices
• What type of structure does fullerene C60 have?

  Molecular structure
• How many carbon atoms are each carbon atom joined to in graphene and fullerene?

  Each carbon atom is joined to 3 others
• Why do diamond and graphene have high melting points?

  A lot of energy is needed to overcome bonds
• What is the melting point of fullerene compared to diamond and graphene?

  Fullerene has the lowest melting point
• Why does fullerene have low strength?

  It has weak forces between molecules
• Why are diamond and graphene considered very strong materials?

  They have lots of strong covalent bonds
• Does diamond conduct electricity?

  No, diamond does not conduct electricity
• Why does diamond not conduct electricity?

  There are no free electrons in diamond
• What allows graphene and fullerene to conduct electricity?

  Each carbon atom has one free electron
• What are delocalised electrons?

  Electrons that are free to move across structures
• How does fullerene conduct electricity?

  Only conducts across the surface of the molecule
• Why is fullerene considered a poor conductor of electricity?

  No movement of electrons between molecules
• describe what will happen to the brightness of the light bulb in a chemical cell over a long period of time

  • starts bright
  • becomes dimmer
  • goes out over time
• describe how the pH of the mixture is determined when a drop of it is placed on the universal indicator paper

  • observe colour produced on universal indicator paper
  • compare to pH chart/scale
• Name a piece of equipment which could be used to measure out 50.0 cm3 of dilute hydrochloric acid more accurately than the measuring cylinder

  • burette/ graduated pipette
• In the method, universal indicator paper is used to determine the pH.

  Explain why litmus paper would not be a suitable indicator to use in this experiment.

  • litmus paper only shows if the solution is acidic/alkaline
  • does not show how acidic or alkaline the solution is
• Explain why solid magnesium carbonate cannot conduct electricity but solid magnesium can.

  • ions in magnesium carbonate cannot move because they are in a fixed position
  • magnesium contains delocalised electrons
  • electrons in magnesium can flow
• state the meaning of actual yield

  • yield of product formed in the reaction
• state the meaning of theoretical yield

  • calculated mass/ yield of product formed using the balanced equation
• Explain the effect on the atom economy of this reaction if the carbon dioxide produced was used to make fizzy drinks.

  • carbon dioxide becomes useful as it is no longer a waste product
  • so atom economy increases
• Explain what should be done to the copper electrodes before their masses are determined.

  • electrodes cleaned using emery paper
  • to remove impurities
• Aluminium is extracted from its ore by electrolysis.

  Explain why this method is used to extract aluminium from its ore.

  • aluminium is high in the reactivity series
  • needs a lot of energy to remove oxygen from the oxide
• Give one disadvantage of phytoextraction as a method of extraction of metals.

  • slow process
  • large area of land required
  • only extracts metal from the ground surface
  • metals need further extraction
• State the change in colour of the methyl orange at the end point when the ammonia solution has just been neutralised.

  from yellow to orange
• Explain other practical steps that should be used in the titration to ensure that an accurate titre volume is obtained.

  • use of a white tile so easier to see precisely when indicator changes colour
  • swirl flask when adding acid, ensures complete mixing of both reactants
  • near end point, add acid slowly in smaller quantities, easier to stop excess acid being added when indicator changes colour
• Explain why graphene will be a good conductor of an electric current.

  • carbon has 4 outer shell electrons
  • 3 electrons used in bond with other carbon atoms
  • one electron free to move/ delocalised
• Explain the meaning of the term weak acid

  • partially dissociated
  • concentration of H+ ions = lower than expected