Chemical Analysis - IR Spectroscopy (10.6)

Question 1

What is spectroscopy?

Answer 1

• any analytical technique that uses the electromagnetic spectrum to probe a material

Question 2

Why is mass spectrometry combine with spectroscopy?

Answer 2

• as a useful analytical method

Question 3

What is IR spectroscopy?

Answer 3

• Infrared (IR) = shone at a sample
• has roughly the same energy as the energy required to make bonds vibrate
• some IR light = absorbed, depending on the bonds present
• some wavelengths are absorbed by the sample as the bonds vibrate
• IR source to Sample to Dectector

Question 4

What is a fingerprint region?

Answer 4

• anything below 1500 cm-1
• only used for direct comparisons - as it is difficult to assign individual peaks in this region
• every molecule contain different bonds, so has a fingerprint characteristic
• used to determine whether 2 samples = identical
  e. g. used to detect forged bank notes

Question 5

What is IR spectroscopy commonly used for?

Answer 5

• quality control on production lines

Question 6

Within IR Spectroscopy, why do chemical bonds vibrate?

Answer 6

• they have different strengths so vibrate with different energies

Question 7

What are characteristics peaks for C=O?

Answer 7

• double bonds between carbon + oxygen vibrates with an energy between 1500cm-1 and 1700cm-1
• gives rise to a very sharp peak with strong absorbance

Question 8

What are characteristics peaks for O-H?

Answer 8

• O-H bond vibrates with an energy between 2500cm-1 and 3500cm-1
• shape of peak depends on the type of OH group present
  e. g. alcohols give a broad peak, independent from C-H peaks
  e. g. 2 carboxylic acids, give a very broad peak that usually covers C-H peaks