2022

• Which is which:

  • butanoic acid
  • 2-methylpropanal
  • 2-methylpropanoic acid
  • 2-methylpropan-1-ol

  Describe how these two steps could be used to identify which compound is which.

  1 ALDEHYDE

  • Tollen's reagent = silver mirror
  • OR Fehling's reagent = orange-red precipitate

  2 ALCOHOL

  • acidified potassium dichromate = orange to green

  3 DISTINGUISHING ACIDS

  • IR spectroscopy (finger-print region)
  • look for exact match to spectra of known compounds
• In Europe, some of the glucose from crops is fermented to produce ethanol. Use of a carbon-neutral fuel leads to no net emissions of carbon dioxide to the atmosphere.

  The ethanol produced by fermentation of glucose may be regarded as a carbon-neutral fuel.

  Justify this statement. Include the relevant chemical equations in your answer.

  6CO2 + 6H2O -> C6H12O6 + 6O2

  C6H12O6 -> 2C2H5OH + CO2

  2C2H5OH + 6O2 -> 6CO2 + 6H2O

  6CO2 taken in and 6CO2 released
• Coffee beans from South America are exported to Europe in an outer layer called silverskin. The waste silverskin can be fermented to produce a solution containing propanone, ethanol and butan-1-ol..

  Suggest why ethanol produced in Europe using silverskin from South America is less likely to be carbon-neutral than ethanol produced from crops grown in Europe.

  Transport has larger carbon footprint
• There is a very low yield of butan-1-ol from but-1-ene in this manufacturing process. Explain why.

  Formed from less stable carbocation (primary not secondary)