13 - synthesis and analysis

Question 1

What does infrared do to molecules?

Answer 1

It makes the bonds bend, stretch and vibrate

Question 2

What is wavenumber?

Answer 2

It relates to the wavelength of the infrared hitting the bonds
unit:cm^-1

Question 3

What does wavenumber tell us?

Answer 3

Different organic molecules have different wavenumbers when they vibrate when IR hits them

Question 4

What 2 properties affect the frequency of bond vibration and in what way?

Answer 4

Heavier atoms cause slower vibration

Stronger bonds cause faster vibration

Question 5

What are the 3 greenhouse gases?

Answer 5

Water

Methane

Carbon dioxide

Question 6

What do greenhouse gases do in terms of IR?

Answer 6

They absorb IR so their bonds vibrate

This causes heat to be given out to the atmosphere

Causing global warming

Question 7

How do we find out what substance a sample is by using IR?

Answer 7

You fire IR radiation at the sample through a range of wavenumbers

A spectrophotometer will look at which wavenumbers were absorbed by the sample (not transmitted)

Question 8

What is the range of wavenumbers used in IR spectroscopy?

Answer 8

4000 cm^-1

To

400 cm^-1

Question 9

What will the spectrophotometer present to the user?

Answer 9

A graph showing wavenumber on the x axis

And percentage transmittance on the y axis

Question 10

How can you work out from the spectroscopy graph what a substance is?

Answer 10

You look at where the transmittance spikes downwards because this tells you which wavenumbers have been absorbed

You can then look at the data sheet and recognise which functional groups are part of the compound because this will be the wavenumbers where transmittance spikes downwards

Question 11

What do we call a downward spike in transmittance?

Answer 11

A peak

Question 12

What are the 2 practical uses of IR spectroscopy?

Answer 12

Analysis of vehicle emissions

Breath test for ethanol

Question 13

What are the 2 uses of mass spectrometry?

Answer 13

To identify the molecular ion

To determine molar mass

Question 14

Give the 5 steps of mass spectrometry

Answer 14

Injection of the sample of molecules as a gas

Ionisation by a electron gun which knocks off electrons from outer shells

Acceleration of positive ions towards electromagnet

Deflection by the electromagnet to change direction of ions

Detection of the different ions and their abundances

Question 15

How does the mass spectrometer differentiate between different ions?

Answer 15

Lighter ions get deflected more than the heavier ions

Question 16

What 2 things does the mass spectrometer measure?

Answer 16

Abundance of ions

m / z ratio of ions

Question 17

What is m / z ratio?

Answer 17

This means mass to charge ratio although the charge is always 1+

So m/z is just the mass of the ion

Question 18

What do you look for on a mass spectrum (the output graph)

Answer 18

The peak which is furthest to the right is the one we are always looking for

Question 19

What is the only exception to looking for the “furthest right” peak?

Answer 19

Sometimes there will a tiny peak which is 1 greater than what are looking for

This is due to carbon-13 isotopes

You have to ignore this tiny peak if it appears

Question 20

What is fragmentation?

Answer 20

The molecular ion in the mass spectrometer is unstable as it passes through and can break into different fragments

Question 21

Which parts of molecular ion break up?

Answer 21

The break can happen anywhere

Question 22

What happens to the positive charge on the molecular ion when it undergoes fragmentation?

Answer 22

The +1 positive charge goes onto either but only one of the fragments

Question 23

What decides which fragment the charge goes to?

Answer 23

It goes to either

It’s random

Question 24

How can you detect fragments in mass spectrometry?

Answer 24

The charged fragment will appear on the mass spectrum

Question 25

State what happens to the molecular ion in fragmentation in exam question terms

Answer 25

It breaks down to a positively charged fragment and a neutral charge radical

Question 26

Define heating under reflux

Answer 26

The continuous boiling and condensing of a mixture back to the original container

Question 27

Why do we use reflux?

Answer 27

To make sure that the reaction takes place without the contents of the flask boiling dry

Question 28

When you purify organic products using a separating funnel, how can you distinguish between organic and aqueous substance?

Answer 28

Aqueous layer is at bottom and organic is at top

Question 29

How do you remove acid impurities after using a separating funnel?

Answer 29

Neutralise using alkali

Question 30

What are the 3 drying agents and what is each used for?

Answer 30

Anhydrous calcium chloride

Anhydrous calcium sulfate

Anhydrous magnesium sulfate

The anhydrous part is very important

The CaSO~4 and MgSO~4 are used for general drying

The CaCl~2 is used for drying hydrocarbons

Question 31

What does it mean if the solid drying agent is sticking together in a clump?

Answer 31

More drying agent needed because there is still water there

Question 32

Once you have added enough drying agent, what do you do?

Answer 32

Decant or filter it

Question 33

When is redistillation used?

Answer 33

When multiple products have similar boiling points

Question 34

In redistillation, which substance do you collect the boiling point of?

Answer 34

The compound you are trying to make

Question 35

What happens to the product when the boiling point range is narrower?

Answer 35

The product will be purer

Question 36

List all the Quickfit apparatus needed in reflux

5 items needed

Answer 36

Pear-shaped flask

Receiver

Screw-tap adaptor

Condenser

Still head