Analytical techniques Module 4

Question 1

What does infra red spectroscopy help you do?

Answer 1

Identify organic molecules
The IR radiation is absorbed by the covalent bonds in the molecules making them vibrate
Different bonds absorb different frequencies so helps you identify which organic molecule it is in total

Question 2

What’s an infrared spectrum?

Answer 2

Graph with transmittance on y axis and wavenumber on x axis

Downward peaks show where bonds are occuring

Question 3

How does infra red spectroscopy in breathalysers work?

Answer 3

Compares C-H peak to O-H peak

Question 4

Another use of infra red spectroscopy?

Answer 4

Measuring amounts of polluting gases in atmostphere

Question 5

How can a mass spectrum be used to identify compounds?

Answer 5

The molecules in the sample are bombarded with electrons to form a molecular ion, M+(g)
Can create graph with relative abundance on y axis, and mass/charge on x axis
To find the relative mass of a compound find the molecular ion peak which will be value furthest up the x axis
(Be careful of M+1 peak, which is formed by presence of Carbon isotope C13)

Question 6

How can the molecular ion be broken into smaller fragments and what can you tell from this?

Answer 6

Bombrading of electrons causes some molecular ions to split
The molecular ion can split in 2 ways show 2 different molecular ions can form
However if one forms then other one is going to be a free radical and is “lost”

Question 7

What is special about the OH peak in a carboxylic acid?

Answer 7

Much broader