Spectroscopy

Question 1

How does a mass spectrometer work

Answer 1

-determines mass of molecules by measuring the mass - to - charge ratio of ions
-the size of the trace produced is dependent in the relative abundance of the ion

Question 2

How is the mass of the molecular ion the same as that of the compound

Answer 2

Mass of electron is negligible

Question 3

What is the definition for the molecular ion

Answer 3

The positive ion formed in mass spectrometry when a molecule loses an electron

Question 4

Which is the molecular ion peak

Answer 4

The clear peak with the highest m/z value on the right hand side of the mass spectrum

Question 5

What is responsible for the M+1 peak

Answer 5

-The very small peak one unit after the m+ peak is known as the m+1 peak and it exists as some of the carbon present is the carbon -13 isotope (1.1%)

Question 6

What is fragmentation

Answer 6

The process in mass spectrometry that causes a positive ion to split into peices , one of which is the positive fragment ion

Question 7

What’s the equation for fragmentation occurring

Answer 7

M+ —-> A+ + B.
Molecular ion —> fragment ion and radical

Question 8

Does the radical produce a peak

Answer 8

No because only the positive ions are detected

Question 9

How do bonds vibrate

Answer 9

The covalent bonds that join atoms in molecules can absorb infrared radiation. This absorbed energy makes the bonds vibrate

Question 10

What are the two ways bonds can vibrate

Answer 10

Bending or stretching motion about a central point

Question 11

What happens to the vibrations with temperature

Answer 11

They increase with temperature

Question 12

How does the amount a bond stretch or bend depend on the mass of the atoms and the bond strength

Answer 12

-lighter atoms vibrate faster
-weaker bonds vibrate slower

Question 13

How do different covalent bonds have different strengths

Answer 13

This is due to the different masses of the different atoms at either end of the bond. This affects bond strength and length

Question 14

What happens as a result of differing bond strengths

Answer 14

The bonds vibrate at their own unique frequency. This is measured as wavenumbers in cm-1

Question 15

What’s the most common frequency

Answer 15

200-4000 this is in the infrared region

Question 16

What is the impact of this on the environment

Answer 16

The suns visible light and ir radiation passes through the atmosphere and reaches the earths surface where it is absorbed. Some of the ir radiation is remitted by the earths surface as longer wavelength ir

Question 17

What are 3 greenhouse gases

Answer 17

Water vapour , methane and carbon dioxide

Question 18

What then happens to the longer wavelength ir

Answer 18

These gases absorb it as it has the same natural frequency as their bonds

Question 19

Then what happens

Answer 19

Eventually the vibrating bonds in these greenhouse gases re emit this energy as radiation- increasing the atmospheric temperature, leading to global warming.

Question 20

What are the dips on the infrared spectrum called

Answer 20

Peaks

Question 21

What can we gather from the peaks

Answer 21

Each peak is at a wavenumber that can be related to a particular bond in the molecule

Question 22

What does a larger peak tell us

Answer 22

The greater the absorbance

Question 23

What are some uses of ir spectroscopy

Answer 23

Identification of particular bonds in a molecule and identification of compounds by direct comparison of spectra

Question 24

What are real world uses of ir spectroscopy

Answer 24

Breathalyser- checking alcohol content in breath
Drug analysis in forensic science
Checking co2 concentrations in the atmosphere and greenhouses