exam questions mistakes

• disadvantages using glass beaker, tripod and gauze:

  • glass poorer conductor than copper
  • Tripod and gauze would reduce heat transfer
  • Tripod and gauze would have a fixed height above the flame
• methods to decrease percentage uncertainty:

  • using more precise instruments
  • using larger volumes or masses
  • increase concentration on solution
• the reason why bond enthalpy calculated is different from the mean bond enthalpy is because: the data book value is derived from a number of different compounds
• suggest how students method and analysis of the results could be improved in order to determine a more accurate value for the enthalpy of reaction (NOT referring too precision of measuring equipment or amounts/ concentrations of chemicals)

  IMPROVED INSULATION:

  insulate beaker or use polystyrene cup/ lid to reduce heat loss

  
  

  IMPROVE TEMPERATURE RECORDING:

  record temperature for a suitable time before adding the metal for accurate initial temp

  
  

  IMPROVE ANALYSIS OF RESULTS:

  extrapolate cooling to point of addition so establish theoretical maximum temperature
• you can measure out the mass of water without using a balance as water has a known density (of 1.0 g cm–3 ) = Therefore, a volume of 50.0 cm3 could be measured out to 50g