Organic analysis 16

Question 1

test for alkene

Answer 1

shake with bromine water

orange colour disappears

Question 2

test for halogenalkane

Answer 2

1 add NaOH(aq) and warm
2 acidify with HNO3
3 add AgNO3(aq)

the precipitate of AgX

Question 3

test for alcohol

Answer 3

add acidified K2Cr2O7

orange colour turns green with primary and secondary alcohols

Question 4

test for aldehydes

Answer 4

warm with Fehling’s solution / Tollen’s solution

blue colour turns red / silver mirror

Question 5

test for carboxylic acid

Answer 5

add NaHCO3(aq)

CO2 given off

Question 6

fragmentation (molecular ion)

Answer 6

many ions will then break up because some of their bond breaks as they are ionised.
each of the fragment creates a line

Question 7

High-resolution mass spectrometry

Answer 7

can measure masses to three or four decimal places you can work out the molecular formula of the parent ion

Question 8

infrared spectroscopy works

Answer 8

• a pair of atoms joined by a chemical bond is always vibrating. (like two balls and a spring)
• stronger bonds vibrate faster and heavier atoms vibrate slower.
• every bond has its own unique natural frequency that is in the infrared region of the electromagnetic spectrum
• when you shine a beam of infrared radiation through the sample, the bonds in the sample can absorb energy from the radiation and vibrate more but can only absorb the energy of the same frequency. radiation that emerges from the sample will be missing the frequencies

Question 9

infrared spectrometer

Answer 9

1 a beam of infrared radiation containing a spread of frequencies is passed through a sample
2 radiation that emerges is missing the frequencies that correspond to the types of bonds found in the sample
3 instrument plots a graph of the intensity of the radiation emerging from the sample against the frequency of radiation
4 frequency expressed as a wavenumber

Question 10

fingerprint region

Answer 10

-area of an infrared specctrum below 1500cm-1
the shape is unique for any particular substance, it can be –idenify the chemical.
-a chemist can use a computer to match fingerprint region of a sample with those on a database of compounds.

Question 11

mass spectrometry

Answer 11

relative atomic mass
ionised, so postive Iona are accelerated through the instrument towards detector
flights of time measure (mass to charge ratio)
used in drug testing
(Mass spectrometry can be used to determine the molecular formula of a compound)

Question 12

GCM’s

Answer 12

gas chromatography mass spectrometry
used in forensic work
separating mixtures of vapours through a tube packed with a powdered solid

Question 13

oxidation state

Answer 13

number of electrons lost or gained by an atom in a compound compared to the uncombined atom

Question 14

what happens in a infrared spectrometer

Answer 14

(Bonds in a molecule absorb infrared radiation at characteristic wavenumbers.
‘Fingerprinting’ allows identi cation of a molecule by comparison of spectra.)