Unit 4Spectroscopy and chromatography

Question 1

What are the different types of analysis?

Answer 1

Infrared, microwaves, ultra-violet and radio waves.

Question 2

How does infrared analysis work?

Answer 2

infra red energy causes bonds to vibrate. This can be used to identify the types
of bond in a molecule

Question 3

How does microwave analysis work?

Answer 3

• certain molecules absorb the microwaves causing them to rotate

Question 4

How does radio waves and NMR analysis work?

Answer 4

It causes the hydrogen nucleus to change its spin state. This can give us
information about the arrangements of hydrogens in a molecule.

Question 5

How can UV light get used in analysis?

Answer 5

UV energy can break bonds such as the Cl-Cl bond or C-Cl

bond

Question 6

When NMR is used, what are the substances dissolved in?

Answer 6

Ones without any H atoms like CCl4

CDCl3

Question 7

Why is tetramethylsilane added to NMR?

Answer 7

It is used to calibrate the spectrum so you know by how much the peaks have shifted by.
TMS is used specifically because
•its signal is away from all the others
•it only gives one signal
•it is non-toxic
•it is inert
•it has a low boiling point and so can be removed
from sample easily

Question 8

What affects the NMR shift of the hydrogen atoms?

Answer 8

The atoms and groups next to the hydrogen. More electronegative shifts give a greater shift.

Question 9

What affects the splitting of a peak?

Answer 9

A the no. of hydrogen’s in a neighboring group plus one.

If a group has a neighboring hydrogen it will split into 2.

Question 10

what is the wavelength of uv light?

Answer 10

400 to 10 nm

Question 11

what is the wavelength of microwave radiation?

Answer 11

1mm to 1m

Question 12

what is the wavelength of waves in a microwave?

Answer 12

12.24 cm

Question 13

How does a microwave work?

Answer 13

The microwaves create an electric field and the polar water molecules try and line up with the field by rotating. This creates collisions and heat energy

Question 14

What are uses of microwaves other than to heat food?

Answer 14

Kill cancer cells

Dry wood paper and textiles as it is more efficient.

Question 15

What are the two different parts found in all chromatography?

Answer 15

mobile phase: where the molecules can move. Always liquid or gas.
Stationary phase: Where the molecules can’t move. Solid.

Question 16

How does gas chromatography work?

Answer 16

Thick liquid is the stationary phase and it covers the inside of a tube.
A gas or liquid sample is vaporised and put carried by a carrier gas, through the tube.
The tube is in a oven
Different parts of the sample are absorbed by the stationary phase by different amounts and so they all have different retention times.
The area under the graph produced gives relative amounts of each component.

Question 17

Explain HPLC

Answer 17

The stationary phase are small particles of solid (silica bonded to hydrocarbons) in a tube.
The polar mobile phase is a liquid (methanol and water) and it goes through the tube carrying the sample.
The retention time is measured by shining UV light through the mixture as it comes out.

Question 18

When can HPLC be used where GC can’t be?

Answer 18

As the substance isn’t heated in HPLC it can be used when the sample has a high boiling point or is heat sensitive.