19A. Modern Analytical Techniques II [SET 1]

Question 1

What is formed in a mass spectrometer?

Answer 1

A molecular ion

Question 2

How is a molecular ion formed?

Answer 2

When a molecule looses an electron

Question 3

What is the m/z value?

Answer 3

The mass/charge ratio

Question 4

What is the m/z value the same as?

Answer 4

The molecular mass

Question 5

What does high resolution mass spectrometry measure?

Answer 5

Precise masses

Question 6

What can high resolution mass spectrometry be useful for identifying?

Answer 6

Compounds that appear to have the same Mr when rounded to the nearest whole number

Question 7

What information does NMR give you?

Answer 7

About the structure of molecules

Question 8

What does NMR stand for?

Answer 8

Nuclear Magnetic Resonance

Question 9

How does NMR work?

Answer 9

A sample of a compound is put into a strong magnetic field and exposed to a range of different frequencies of radio waves
Nuclei of certain atoms absorb energy from the radio waves

Question 10

What information does Carbon-13 NMR give you?

Answer 10

About the number of carbon atoms that are in a molecule, and the environments that they are in

Question 11

What information does High resolution Proton NMR give you?

Answer 11

About the number of hydrogen atoms that are in a molecule and the environments that they are in

Question 12

What does the amount of energy that a nucleus absorbs depend on?

Answer 12

The environment that it is in

Question 13

What is a nucleus shielded by?

Answer 13

Its surrounding electrons

Question 14

What can electron shielding be affected by?

Answer 14

The other atoms and groups of atoms around the nucleus

Question 15

How would an electronegative element affect the electron shielding?

Answer 15

It would reduce it, as the electrons would be drawn away

Question 16

What does an atom’s environment depend on?

Answer 16

All the groups that it is connected to

Question 17

What is used as a standard in NMR?

Answer 17

Tetramethylsilane - TMS

Question 18

What are absorbances measured relative to?

Answer 18

TMS

Question 19

Why is TMS used as a standard?

Answer 19

Because its absorption peak is at a lower frequency than all other molecules

Question 20

What is chemical shift?

Answer 20

The difference in the radio frequency absorbed by the nuclei in the molecule being analysed and by the same nuclei as in TMS

Question 21

What does the number of peaks on a C13 NMR spectrum show you?

Answer 21

The number of carbon environments

Question 22

What do the chemical shifts show you?

Answer 22

The different carbon nuclei

Question 23

What does proton NMR tell you?

Answer 23

The number of hydrogen environments

Question 24

What splits the peaks in C13 NMR?

Answer 24

Spin-spin coupling

Question 25

Which hydrogens can affect splitting?

Answer 25

Only those on the adjacent carbon

Question 26

What would a triplet peak indicate?

Answer 26

That there are two hydrogens in adjacent carbons

Question 27

What do integration traces show?

Answer 27

The ratio of protons in each environment - the relative areas under each peak is the relative number of H atoms in each environment

Question 28

What can proton NMR be used to work out?

Answer 28

Structures

Question 29

What is chromatography useful for?

Answer 29

Separating and identifying things

Question 30

What is a mobile phase?

Answer 30

Where the molecules can move, always a liquid or a gas

Question 31

What is a stationary phase?

Answer 31

Where the molecules can’t move, must be a solid, or a liquid on a solid support

Question 32

What is the basic principle of chromatography?

Answer 32

Mobile phase moves through or over the stationary phase
The distance each substance moves up the plate depends on its solubility in the mobile phase and its retention by or adsorption to the stationary phase
Components more soluble will travel further

Question 33

What does the distance each substance moves depend on?

Answer 33

The solubility in the mobile phase and the retention or adsorption to the stationary phase

Question 34

What can Rf values be useful for?

Answer 34

Identifying compounds in a mixture

Question 35

How would you calculate an Rf value?

Answer 35

Distance travelled by spot/distance travelled by solvent

Question 36

What can affect Rf values?

Answer 36

Composition of the paper, the solvent or the temperature

Question 37

Why would spots of two different substances be put on the same paper?

Answer 37

Because conditions are difficult to keep identical

Question 38

What is HPLC?

Answer 38

High Performance Liquid Chromatography

Question 39

What conditions is HPLC done under?

Answer 39

High pressure

Question 40

What is usually the stationary phase in HPLC?

Answer 40

Silica bonded to various hydrocarbons

Question 41

What is often the mobile phase in HPLC?

Answer 41

A polar mixture of methanol and water

Question 42

Why does HPLC separate the mixture into different parts?

Answer 42

Because they are attracted by different amounts to the solid, so take different lengths of time to travel through the column

Question 43

What happens as the liquid leaves the HPLC column?

Answer 43

UV light is passed through it and absorbed by parts of the mixture

Question 44

What does a HPLC chromatogram show?

Answer 44

The retention times of the components of the mixture

Question 45

What is the mobile phase in gas chromatography?

Answer 45

A gas

Question 46

What happens to gases as they move through gas chromatography?

Answer 46

They constantly dissolve in the oil or adsorb onto the solid, evaporate back into the gas then redissolve as they travel through