Mass Spectrometry,Infrared Spectroscopy and Organic Analysis

Question 1

How is the mass spectrum used to determine the Mr of a compound

Answer 1

Find the m/z value of the peak with the highest m/z

Question 2

Molecular ion peak

Answer 2

Peak with highest m/z value

Question 3

Base peak

Answer 3

Peak with highest relative intensity. Represents most stable fragment

Question 4

Use of mass spectrometry outside of the lab

Answer 4

Breathalysers
Monitoring air pollution

Question 5

How does the height of the peak tell you the abundance of the isotope

Answer 5

The height of the peak is directly proportional to the abundance of the isotope

Question 6

What is above 1500cm-1 used to show in infrared spectroscopy

Answer 6

Specific groups in a molecule which absorb infrared radiation at characteristics frequencies

Question 7

What does below 1500 represent in infrared spectroscopy and why is it significant

Answer 7

FIngerprinting region - this region is unique for every compound so is used to identify compounds

Question 8

How is the fingerprint region used to identify and distinguish between compounds

Answer 8

A computer will compare the IR spectra of the fingerprint region against a database of known pure compounds to identify the compound.

Question 9

How to identify an alkene

Answer 9

Reagent : Bromine water
Result : Orange colour decolourises

Question 10

How to identify an aldehyde

Answer 10

Reagent : Fehling’s solution
Results : Blue solution to red precipitate

Reagent : Tollen’s reagent
Results : Silver mirror

Question 11

How to identify a carboxylic acid

Answer 11

Reagent : Sodium carbonate
Results : Effervescence due to CO2 formed

Question 12

How to identify a primary/secondary alcohol

Answer 12

Reagent : acidified potassium dichromate
Results : Orange to green colour change

Question 13

How to identify a chloroalkane

Answer 13

Reagent : Warm with silver nitrate
Results : Slow formation of white precipitate of AgCl

Question 14

At what do bonds in a molecule absorb infrared radiation

Answer 14

At characteristic wavenumbers

Question 15

Why do carbon dioxide, methane and water vapour absorb infrared radiation

Answer 15

It has same frequency as the natural frequency of their bonds

Question 16

How can you confirm using IR spectroscopy that the spectrum given to you was ethanol

Answer 16

Run an infrared spectrum for a known sample of ethanol. Then compare the two spectra. They will have an identical absorption pattern in the fingerprint region

Question 17

Describe how the fingerprint region can be used to identify a compound

Answer 17

Compare the spectrum of the unknown compound with the spectrum of a known compound from a database. The 2 spectra will have an identical absorption pattern in the fingerprint region

Question 18

What does an O-H bond look like in an infrared spectrum

Answer 18

Broad absorption peak

Question 19

Why is infrared radiation linked to climate change/global warming

Answer 19

Greenhouse gases like CO2 and methane and water vapour absorb infrared radiation and are associated with warming the atmosphere

Question 20

Why does C=O absorb infrared radiation

Answer 20

It has polar bonds

Question 21

What do impurities look like in an infrared spectrum

Answer 21

Rogue absorptions