Ocr Chemistry Unit 1: Module 3 - Analysis

Front 1

Chromatography

Describe the process of chromatography

Back 1

1) Place the chromatography plate in the tank with a sample line at the bottom

2) Ensure the solvent level is below the sample line

3) Cover the tank and leave until the solvent front has reached the top of the plate

4) Remove the plate and mark the position of the solvent front

Front 2

Chromatography

Name some uses of chromatography

Back 2

Analysis of drugs, plastics, flavourings, foods, forensics, air samples, fuels etc

Front 3

Chromatography

What are some benefits of chromatography?

Back 3

Only small samples are needed

After separation, the pure components can be analysed precisely using other analytical methods.

Front 4

Chromatography

What are the two types of chromatography you need to know?

Back 4

Thin-layer

Gas

Front 5

Chromatography

Generally describe the 'science' behind chromatography

Back 5

A mobile phase sweeps a mixture over a stationary phase.

It works on the basis that different components have different AFFINITIES for stationary phases and mobile phases:

the stationary phase interacts with the components in the mixture, slowing them down. More interaction = more slowed down.

This allows different components to flow over the stationary phase at different speeds, separating them.

Front 6

Chromatography

What is the state of the stationary and mobile phase in TLC?

Back 6

Stationary - Solid

Mobile - Liquid

Front 7

Chromatography

What is the state of the stationary and mobile phase in GC?

Back 7

Stationary - Liquid/solid on solid support

Mobile - Gas

Front 8

Chromatography

What does a solid stationary phase separate components by? Define.

Back 8

ADSORPTION - the process by which a solid holds molecules of a gas/liquid or solute as a thin film on the surface of a solid

Front 9

Chromatography

Draw diagrams to represent separation by adsorption and by relative solubility

Back 9

Front 10

Chromatography

What is the stationary phase in TLC?

Back 10

A thin layer of an adsorbant such as silica gel (SiO2) or Alumina (Al2O3) coated on a flat, inert support - a TLC plate, often a sheet of glass/plastic.

Front 11

Chromatography

What is the mobile phase in TLC?

Back 11

A liquid solvent.

Front 12

Chromatography

Rf = ?

Back 12

Rf = Distance moved by solvent / Distance moved by solvent front

Front 13

Chromatography

What can you use Rf values for?

Back 13

To identify an unknown compound by comparing known Rf values.

Front 14

Chromatography

What are the limitations of TLC?

Back 14

- Similar compounds often have similar Rf values

- Unknown compounds will have no reference Rf to compare to

- It may be difficult to find a solvent that separates all the components in a mixture- too soluble in solvent = washed up with solvent front

little solubility = components will hardly move.

Front 15

Chromatography

What is GC useful for?

Back 15

To separate volatile compounds - useful for compounds with low boiling points and evaporate easily.

Front 16

Chromatography

Describe the stationary and mobile phase in GC.

Back 16

STATIONARY - Thin layer of liquid/solid coated inside capillary tubing which acts as an inert solid support.

Tubing (the chromatography column) is coiled so it fits in a thermostatically controlled oven.

The liquid stationary phase is often a long-chain alkane with a high boiling point.

Solid stationary phases include silicone polymers.

MOBILE PHASE - Carrier gas which moves through the column. An inert or inactive gas such as He or N.

Front 17

Chromatography

Describe the process of GC.

Back 17

1) Mixture is injected into the gas chromatogram, where it is vaporised.

2) Mobile carrier gas flushes the mixture through the column

3) As the mixture moves through the column, components slow down as the interact with the stationary phase coating the column. (liquid = dissolve, solid = adsorb) Greater solubility/adsorption = more slowed down

4) Components separate and each leaves the column at a different time and is detected as it leaves, a computer processes these results.

Front 18

Chromatography

What is the retention time? + function

Back 18

The time for a component to pass from the column inlet to the detector.

Can be used to identify an unknown substance if compared with known retention times

Front 19

Chromatography

What are the limitations of GC?

Back 19

- Many chemicals may have similar retention times, peak shape and detector response so GC might not identify them

- Not all substances will be separated and detected - a small amount of a substance can hide beneath another that has a higher conc and the same retention time

- Unknown compounds have no retention times for comparison

Front 20

Chromatography

Describe GCMS.

Back 20

GC - separates components, but can't identify them conclusively

MS - provides detailed structural info on most compounds but cannot separate them

1)Components in a mixture are first separated by GC. Retention time provides an initial identification

2) Separated components are put in a MS where they are detected

3) MS is analysed or compared with a spectral database

Front 21

Chromatography

What is GCMS used for?

Back 21

Forensic and drug analysis, environmental analysis, airport security and space probes.

Forensics = analysis minute particles found at a crime scene.

Environmental = Pollutants, quality of water, pesticides in food.

Airports = Explosives

Space = analyse atmosphere, material

Front 22

NMR

What is the purpose of NMR?

Back 22

Examining molecular structure.

Front 23

NMR

What is chemical shift?

Back 23

The place in an NMR specturm at which a nucleus absorbs energy

Front 24

NMR

What is chemical shift measured relative to?

Back 24

A reference signal from Tetramethylsilane TMS (CH3)4Si

Chemical shift = 0

Front 25

NMR

What is the problem with using a solvent for NMR?

Back 25

Organic solvents contain C and H which produce a peak themselves.

Front 26

NMR

What is used as solvents?

Back 26

Deuterated solvents are used as they do not produce a signal.

Front 27

NMR - CARBON 13

In C13 NMR, what does chemical shift indicate?

Back 27

The chemical environments of the carbon atoms present.

The presence of an electronegative element causes significant change in chemical shift.

Front 28

NMR - CARBON 13

In C13 NMR:

a) Peaks show..?

b) Chemical shifts show..?

c) Size of peaks show..?

Back 28

a) Number of different carbon environments

b) Types of carbon environments

c) nothing.

Front 29

NMR- PROTON

In proton NMR:

a) Number of peaks show..?

b) Chemical shifts show..?

c) Size of peaks show..?

d) Splitting shows..?

Back 29

a) Number of proton environments

b) Type of proton environment

c) Relative peak area = proportions of protons in each environment

d) Information of adjacent protons

Front 30

NMR- PROTON

What is the N+1 rule?

Back 30

For n protons on an adjacent carbon, the number of peaks on a splitting pattern is N+1.

Front 31

NMR- PROTON

In proton NMR what happens when a deuterated solvent is added?

Back 31

Any peaks for OH and NH disappears because it exchanges with the H present in OH or NH.

Front 32

NMR- MEDICINE

Describe MRI.

Back 32

Patient is placed in a large, cylindrical electromagnet and radio waves are then sent through the body, Protons align with or against the strong magnetic field and they resonate in response to pulses of radio-frequency radiation.

Front 33

NMR - MEDICINE

What are the advantages of MRI?

Back 33

- Harmless

-Non-invasive

Front 34

NMR - MEDICINE

What are the disadvantages of MRI?

Back 34

- Some patients with ferromagnetic metal implants of pacemakers should not be subjected to MRI.

Front 35

NMR - MEDICINE

What are the uses of MRI in sport?

Back 35

Used to identify injuries.

Front 36

Combined techniques

What is the function of mass spec?

Back 36

determine molecular mass of a compound.

Front 37

Combined techniques

What is the function of IR?

Back 37

Gives information about the bonds present in a molecule and the likely functional groups present.