Analytical techniques

Question 1

How are compounds identified?

Answer 1

Mass spectrometry

Question 2

How is a mass spectrometer used to identify compounds

Answer 2

• Used to determine the relative molecular mass of a compound
• A molecular ion is formed when a molecule looses an electron
• The molecular ion produces a molecular ion peak of the compound
• The mass/charge of the molecular ion peak will be the same as the molecular mass of the compound

Question 3

What is a high resolution mass spectrometer

Answer 3

Measure atomic and molecular masses extremely accurately

Question 4

What is the use of high resolution spectrometers

Answer 4

useful for identifying compounds that appear to have the same Mr

Question 5

What method is used to identify organic molecules

Answer 5

infrared spectrometry

Question 6

How is infrared spectroscopy used to identify organic compounds

Answer 6

Infrared radiation is absorbed by the covalent bonds in the molecules, increasing their vibrational energy

Question 7

What are the 2 principles about how bonds absorb frequencies

Answer 7

• Bonds between different atoms absorb different frequencies of IR radiation

• Bonds in different places in a molecule absorb different frequencies too

Question 8

How is wave number calculated

Answer 8

1/wavelength

Question 9

What does an infrared spectrometer produce

Answer 9

• A graph that shows you what frequencies of radiation the molecules are absorbing to identify the functional groups

Question 10

Where do the peaks on the IR spectra point?

Answer 10

Downwards

Question 11

What do the peaks show

Answer 11

Where radiation is being absorbed

Question 12

What does the fingerprint region identify?

Answer 12

Molecules

Question 13

What will any impurities show in the fingerprint region

Answer 13

• Produce extra peaks

Question 14

Describe how infrared radiation absorption is linked to Global warming

Answer 14

• Electromagnetic radiation emitted by the sun reaches the earth

• The earth re-emits some of it as infrared radiation (heat)

• Some of the greenhouse gases e.g CO2, methane and water vapour absorb this infrared radiation and re-emit it

• This keeps us warm and it’s called the greenhouse effect

• Burning fossil fuels and leaving waste in landfills causes a rise in green house gas concentration

• More heat is being trapped and the earth gets warmer- Global warming

Question 15

How can you distinguish between two structural formulas

Answer 15

Draw them out

Question 16

In what instance can the Mr value in high resolution mass spectrometry not distinguish between two compounds

Answer 16

When the compounds have the same molecular formula

Question 17

State why the precise relative atomic mass quoted in the table for the C12 isotope is exactly 12.00000

Answer 17

Carbon-12 is the standard/ reference value/isotope