Organic Analysis

Question 1

CO2 Test

Answer 1

Bubble through lime water
Solution turns cloudy

Question 2

H2 Test

Answer 2

Apply a lit splint
A squeaky ‘pop’ occurs

Question 3

O2 Test

Answer 3

Apply a glowing splint
The splint will re-light

Question 4

CO32- Test

Answer 4

Add H2SO4
Effervescence (as CO2 is given off)

Question 5

High/ Low Resolution Mass Spectrometry

Answer 5

high= measure to 1 dp
low= measure to 5 dp

Question 6

Why can’t a mass spectrometer which measures m/z ratios to 1 decimal place tell the difference between C10H16O4 and C11H4O4?

Answer 6

They have the same molecular mass to 1 decimal place

Question 7

Why can’t high resolution mass spectrometry tell the difference between propan-1-ol and propan-2-ol?

Answer 7

They have the same molecular formula, so their molecular mass will be exactly the same

Question 8

Why does C have a relative molecular mass of 12.00000?

Answer 8

12C is a standard reference

Question 9

Infrared Spectrometry

Answer 9

Infra red energy is absorbed by bonds which makes the bonds vibrate.
The bonds vibrate at the same frequency as the Infra red energy

Question 10

Inside IR spectrometer

Answer 10

IR passed through sample
Some IR radiation absorbed, some transmitted
Detector plots spectra of IR intensity

Question 11

Example answer

Answer 11

“The spectrum represents a ketone because it has an absorption matching the C=O bond from 1680-1750cm-1”

Question 12

Why does the spectrum represents a ketone and not a carboxylic acid?

Answer 12

‘because it has an absorption matching the C=O bond from 1680-1750cm-1 but no O-H peak from 2500-3000 cm-1’

Question 13

What happens to CO2 when IR hits it?

Answer 13

O-H bonds in water, C=O bonds in CO2, C-H bonds in methane absorb IR radiation
IR emitted by earth not allowed to escape into atmosphere

Question 14

Distinguishing between Propan-1-ol and Propan-2-ol

Answer 14

These both contain the O-H alcohol
A computer database can be used on the fingerprint region below 1500cm-1 to identify which sample is which alcohol.

Question 15

How can mass spectrometry be used to confirm that a compound is definitely ethyl butanoate?

Answer 15

Compare with a known spectrum from a database, it should be an exact match

Question 16

Identifying Impurities

Answer 16

Spectrum A is for pure caffeine.
The sample used to make spectrum B must be impure as it has a broad additional peak.
You cannot necessarily tell what the impurity is though