3.6 Organic Analysis Flashcards
AgBr(s) and AgI(s)
-state reagent to distinguish between them and state observations
reagent : concentrated ammonia
observation with AgBr : will dissolve
observation with AgI : will not dissolve
HCl(aq) and HNO3(aq)
- state reagent to distinguish between them and state observations
reagent : AgNO3
HCl : white precipitate
HNO3 : no observed change
Butanal and butanone
- state reagent to distinguish between them and state observations
reagent : tollens or fehlings solution
observation with butanal : blue solution to brick red ppt forms or silver mirror forms
observation with butanone : no observed change
Isomer 3 = 3-methylbut-1-ene
Isomer 4 = 2-methylbut-2-ene
State one way that the infrared spectrum of Isomer 3 is different from the infrared spectrum of Isomer 4.
Fingerprint region below 1500am^-1 will be different
Butanone
There is a peak between 1680 - 1750 cm^-1
Matches a Peak for C=O
No peak between 3250 to 3550 cm^-1
So no O-H alcohol peak
Two alcohols are formed by the hydration of Isomer 4.
Draw the displayed formula for the alcohol formed that is oxidised readily by acidified potassium dichromate(VI).
Isomer 4 : 2-methylbut-2-ene
- don’t make it tertiary as tertiary alcohols are resistant to oxidation by acidified potassium dichromate
Compound Q has the molecular formula C4H7ClO. It is a volatile liquid which does not produce misty fumes when added to water.
Suggest how the chemist could obtain a sample of Q for analysis from the mixture of volatile liquids.
Distillation
The mass spectrum of C4H7ClO contains two molecular ion peaks at m/z = 106 and m/z = 108. It also has a major peak at m/z = 43.
Suggest why there are two molecular ion peaks.
Chlorine has two isotopes
Identify an absorption that would enable you to distinguish between methyl ethanoate and ethanoic acid.
O-H in the acid
- absorption between 2500 to 3000cm^-1
State how infrared spectroscopy can be used to show that an unknown ester is definitely methyl ethanoate.
Compare with a known spectrum and if it matches
yellow ppt is AgI
Ag^+ + I^- -> AgI
NaCl
) Some scientists thought that the waste water from a waste disposal factory contained two sodium halides. They tested a sample of the waste water.
The method that the scientists used could not detect one type of halide ion. Identify this halide ion. Give one reason for your answer.
Fluoride ion
AgF is soluble as no ppt forms
What is observed when barium reacts with sulfuric acid
Give a use for barium sulfate in medicine and explain why this use is possible, given that solutions containing barium ions are poisonous
white precipitate forms
Barium meal / to block x-rays
BaSO4 is completely insoluble
Draw the displayed formula for the repeating unit of polyethene
Name this type of polymer
State the meaning of the term molecular ion.
The molecule within one electron removed
State why the precise relative atomic mass for the 12C isotope is exactly 12.00000
This is the standard reference or by the definition
(i) more absorption of IR radiation by water
(ii) CO2 contains C=O bond
Peak for C=O is missing at 1680 to 1750 cm^-1
Which box shows for cyclohexene
3rd box
As there is a small peak but a peak between 1620 - 1680 cm^-1 for the C=C bond
Cyclohexanol can be converted into cyclohexanone
Give a reagent or combination of reagents that can be used for this reaction and state the type of reaction.
Acidified K2Cr2O7
Oxidation / redox
Name the reagent that the student could use to identify the sample that was pentanoic acid.
Describe the observation that the student would make to confirm this.
Reagent = sodium carbonate
observation = effervescence
What is formed when propanal is oxidised
propanoic acid
a ketone can be an isomer of an aldehyde. State what type of isomerism is shown
functional group isomerism
- skip empirical formula
No C=O bond at 1680 - 1750
Reagent and observation used to test for an alcohol
- what type of alcohols does it not work for
Reagent : acidified potassium dichromate
observation : solution turns from orange to green
- however it does not work for tertiary alcohols
state reagents and observations used to distinguish between
Aqueous silver nitrate and aqueous sodium nitrate
Reagent : HCl
Observation with silver nitrate : white ppt formed
observation with sodium nitrate : no visible change
