Infrared spectroscopyEdexcel A-Level Chemistry: Mind map

Exam questions on Infrared spectroscopy

1. An organic compound P has the molecular formula C₃H₆O. A student records its infrared spectrum and finds a strong absorption at 1715 cm⁻¹ and no absorption between 3200 and 3600 cm⁻¹.
   Explain why the infrared spectrum cannot distinguish between propanal and propanone, and describe a chemical test that does.2 marks
2. A chemist is given two colourless liquids, ethanol and ethanoic acid, whose labels have fallen off. She records an infrared spectrum of each.
   Describe how the two spectra differ, so that the chemist can identify each liquid.2 marks
3. A student heats propan-1-ol with acidified potassium dichromate(VI) and distils off the product as soon as it forms. The infrared spectrum of the distillate shows absorptions at 2980 cm⁻¹ and 1725 cm⁻¹ only, apart from the fingerprint region.
   Identify the bonds responsible for the two absorptions, and state what the absence of any absorption at 3200–3600 cm⁻¹ shows about the distillate.3 marks