QUICK PRACTICE QUESTIONS

• explain why a pipette is used to measure the sodium hydroxide solution bye a burette is used to measure the citric acid solution 


  pipette measures one fixed volume. Burette measures variable volume
• ionic equation for neutralisation reaction

  H+(aq) + OH- (aq) -> H20 (l)
• 4 marker titration required practical

  add indicator e.g methyl orange in conical flask. with swirling. Use indicator changes from yellow to red
• methyl orange changes colour from yellow to red at pH =7
• why does using a glass beaker instead of polystyrene cup cause the systematic error 


  glass is a conductor
• suggest how the in investigation could be improves to make sure the reaction is complete

  reheat and reweigh until constant mass
• The reaction is exothermic

  Explain in terms of bonds broken and bonds formed


  because energy is released when bonds are formed than is needed to break bonds

  
  

  OR

  
  

  energy is taken in, energy is given out when bonds are made, the energy given out is greater than the energy taken in.
• Why do alkaline batteries eventually stop working?


  reactant is used up
• Why can alkaline batteries


  notbe recharged?reaction is not reversible
• Hydrogen fuel cells


  - better for the environment

  - provides clean source of water

  - H20 is the by product

  - less energy

  - doesn't need to be recharged

  - often made from fossil fuels

  - takes up space
• rechargeable batteries


  - cheaper

  - not flammable

  - smaller

  - can provide more energy

  - contain toxic chemicals
• reactivity series mnemonic


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• Why do non-rechargeable batteries stop working?

  The reactants get used up and the chemical reactions stop
• word equation for hydrogen fuel cell

  hydrogen + oxygen - water
• why can rechargeable batteries be recharged?

  We can reverse the chemical reactions when we apply an electrical current
• why is hydrogen fuel cells seen as non-polluting?

  - don't produce carbon dioxide

  - water is not polluting
• what is an alkaline fuel cell?


  contains OH- ions
• Half equations that take place for the reactions that occur at the electrodes in a hydrogen fuel cell


  H2 →2H+ +2e−

  O2 +4H+ +4e− →2H2O
• What type of energy is released by hydrogen fuel cells?


  electrical
• explain how incomplete combustion of methane can be dangerous


  carbon monoxide is produced

  which prevents oxygen carried in the blood
• explain why the positive electrode must be continually replaced 


  electrode reacts with oxygen. electrode is carbon so carbon dioxide is produced
• explain why the excess hydrogen must be burned off 


  to prevent hydrogen escaping into the air because hydrogen is explosive
• It is common to use an excess of one reactant.

  Explain why a reactant is used in excess


  (So that) the other reactant

  is completely used up
• Suggest one reason why the calculated yield of bromine might not be obtained.


  the reaction is not complete
• example of dependent variable 


  temperature change
• example of independent variable 


  type of metal
• what is a control variable 


  something that is not changed during the reaction, has to be kept constant
• Suggest what is meant by the term “diatomic element”.


  Molecule containing two atoms
• Covalent bonding


  share electrons
• Metallic bonding

  Positive ions surrounded by delocalised

  electrons
• ionic bonding

  Strong electrostatic forces of attraction
• Sodium chloride is an ionic compound.

  Explain why ionic compounds are usually solid at room temperature.

  Strong electrostatic forces

  which require a lot of energy to overcome
• Compare the properties of copper and graphite to decide which material would be better for making the wire.


  Graphite properties

  • conducts electricity

  • soft

  • slippery

  • brittle

  • high melting point Copper properties

  • can be bent /malleable

  • ductile

  • strong / not brittle

  • conducts electricity

  • high melting point
• The surface of some metals, such as iron, corrode when exposed to the air. Explain how this affects the electrical conductivity of the metal.


  Conductivity will decrease

  as an ionic compound is formed

  which will not conduct electricity when solid
• Explain why ionic liquids are used in batteries but solid ionic compounds are not.

  In ionic liquids, ions are able to move

  (so) ions carry charge

  (however) in a solid, ions are unable to

  move
• Explain, in terms of particles, why liquid iodine does not conduct electricity.


  Iodine has no delocalised electrons

  Iodine has no ions

  so cannot carry charge
• Give one ethical reason why a compound of iodine should not be added to food.

  People should have right to choose

  Insufficient evidence of effect on people
• Give three properties of ionic compounds that the student may have found.


  High melting point

  Conducts electricity when molten / dissolved

  Does not conduct when solid