Organic Analysis

Question 1

What is mass spectrometry used for?

Answer 1

To find the abundance and mass of each isotope in an element so we can find the relative atomic mass.
To find the relative molecular mass of substances made of molecules

Question 2

What are the stages of ToF spectrometry?

Answer 2

Ionisation, acceleration, flight tube and detection

Question 3

What are the two forms of ionisation?

Answer 3

Electron impact and electrospray ionisation

Question 4

Explain how electron impact ionisation works

Answer 4

Sample is vapourised and high energy electrons are fired at it from an electron gun which knocks off an electron to form a +1 ion

Question 5

What is an electron gun?

Answer 5

A hot wire filament with a current running through it which emits electrons

Question 6

Write an equation for electron ionisation of a sample

Answer 6

X + e- —–> X+ +2e-

Question 7

What kind of samples is electron impact used for?

Answer 7

Those with low formula mass

Question 8

Explain how electrospray ionisation is used

Answer 8

Sample dissolved in a volatile solvent (water/methanol) and injected through a fine hypodermic needle to give a fine mist. The tip of the needle is connected to the +ve terminal so the sample gains a proton as they leave the needle

Question 9

Write an equation for electrospray ionisation of a sample

Answer 9

X + H+ —-> XH+

Question 10

Why is electrospray ionisation known as soft ionisation?

Answer 10

Fragmentation rarely takes place

Question 11

Why are +ve ions accelerated using an electric field?

Answer 11

To ensure they all have the same kinetic energy

Question 12

What does the velocity of each particle depend on?

Answer 12

Their mass

Question 13

What is the trend between mass and velocity of particles?

Answer 13

Lighter particles have a faster velocity and heavier ones have a slower velocity

Question 14

What happens in the flight tube?

Answer 14

+ve ions travel through a hole in the -vely charged plate into a tube. They set off at the same time but the lighter ions travel faster and start to separate out so they reach the detector first

Question 15

What happens in detection?

Answer 15

+ve ions hit the -ve plate and they gain an electron to become neutral. movement of electrons creates current which can be measured to calculate how many ions hit the plate.

Question 16

What are on the axis of the mass spectrum?

Answer 16

x axis - mass over charge

y axis - abundance

Question 17

When an element goes through the mass spectrum why are there lots of lines?

Answer 17

Due to isotopes of the element

Question 18

When an organic compound goes through the mass spectrum why are there lots of lines?

Answer 18

Due to fragment ions and the original molecule

Question 19

What is the molecular ion?

Answer 19

The line with the largest m/z value which has been produced by the molecule which has only lost one electron

Question 20

What is the cause of more than one molecular ion peak?

Answer 20

When there are isotopes in the molecule that affect the mass

Question 21

Why is high resolution mass spectrometry used?

Answer 21

To distinguish between compounds which have the same Mr to one dp by using 4dp

Question 22

Why is the Ar of C12 exactly 12.0000?

Answer 22

Because the relative atomic masses of all other elements are measured relative to the C12 isotope.

Question 23

What is the natural frequency of vibration of the bond?

Answer 23

The frequency that a covalent bond naturally vibrates at that is within the infrared region of the EM spectrum

Question 24

How does infrared radiation?

Answer 24

IR radiation shone onto an organic compound. The bond only absorbs radiation that has the same frequency as the natural frequency of the bond

Question 25

Why are the internal reflecting and refracting surfaces made from sodium chloride crystals in an IR spectrometer?

Answer 25

Because glass and quartz absorb IR radiation

Question 26

What is the fingerprint region and why is it special?

Answer 26

The area of the spectrum below the 1500cm-1 and it’s special because it’s specific to that molecule.

Question 27

How can you use IR spectra to check the purity of a compound?

Answer 27

When the IR spectrum of a known compound produces extra peaks it shows that it is impure.

Question 28

Name three greenhouse gases

Answer 28

carbon dioxide, water vapour and methane

Question 29

How do the greenhouse gases cause global warming?

Answer 29

Absorb IR radiation bc the bonds in the gases are v good at absorbing IR

Question 30

What is the reagent and observations of the test for alkenes?

Answer 30

Add to bromine water and should go from orange to colourless

Question 31

What is the reagent and observations of the test for primary alcohols?

Answer 31

Acidified potassium dichromate (VI) turns from orange to green

Question 32

What is the reagent and observations of the test for secondary alcohols?

Answer 32

Acidified potassium dichromate (VI) remains orange

Question 33

What is the reagent and observations of the test for aldehydes?

Answer 33

Tollens goes from colourless to silver precipitate on the sides of the mirror (silver mirror)
Fehling’s solution goes from blue to orange

Question 34

What is the reagent and observations of the test for carboxylic acids?

Answer 34

Solid sodium carbonate goes from white solid to the solid disappears and effervesence. Gas turns lime water from colourless to cloudy.

Question 35

What types of organic compounds are soluble in water?

Answer 35

Short chain alcohols and carboxylic acids