Analytical Techniques

Question 1

What happens when a molecule absorbs infrared radiation?

Answer 1

It makes the covalent bond vibrate more in a stretching or bending motion.

Question 2

What factors affect the amount of vibration of a bond?

Answer 2

• bond strength
• bond length
• mass of each atom in the bond

Question 3

How does infrared spectroscopy work?

Answer 3

Every bond has a unique vibration frequency in the infrared region of the EM spectrum
Bonds absorb radiation that has the sane frequency as their frequency of vibration
Infrared radiation emerged from a sample is missing the frequencies that have been absorbed —> this information can be used to identify the compound’s functional group

Question 4

What do the peaks on an infrared spectrum represent?

Answer 4

Absorbance of energy from the infrared radiaton

Question 5

What happens inside a mass spectrometer?

Answer 5

• organic compound is vaporised and passed through the spectrometer
• some molecules lose an electron and forms molecule ons
• excess energy from the ionisation makes the bonds vibrate more
• vibration causes bond to weaken
• molecule ion splits by fragmentation

Question 6

Is fragmentation predictable? Why?

Answer 6

No, because it can happen anywhere in the molecule.

Question 7

What is the advantages of using mass spectrometry? (2)

Answer 7

• cheap
• small quantities of samples required

Question 8

What is the main disadvantage of using mass spectrometry?

Answer 8

The sample is completely destroyed