3.6 Organic Analysis

Question 1

State functional group A

Answer 1

O-H alcohols

Question 2

State functional group of f and e

Answer 2

E =C-H
F = C=O

Question 3

AgBr(s) and AgI(s)
-state reagent to distinguish between them and state observations

Answer 3

reagent : concentrated ammonia
observation with AgBr : will dissolve
observation with AgI : will not dissolve

Question 4

HCl(aq) and HNO3(aq)
- state reagent to distinguish between them and state observations

Answer 4

reagent : AgNO3
HCl : white precipitate
HNO3 : no observed change

Question 5

Butanal and butanone
- state reagent to distinguish between them and state observations

Answer 5

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

Question 6

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.

Answer 6

Fingerprint region below 1500am^-1 will be different

Question 7

Answer 7

Question 8

Answer 8

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

Question 9

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

Answer 9

• don’t make it tertiary as tertiary alcohols are resistant to oxidation by acidified potassium dichromate

Question 10

Answer 10

Question 11

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.

Answer 11

Distillation

Question 12

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.

Answer 12

Chlorine has two isotopes

Question 13

Identify an absorption that would enable you to distinguish between methyl ethanoate and ethanoic acid.

Answer 13

O-H in the acid
- absorption between 2500 to 3000cm^-1

Question 14

State how infrared spectroscopy can be used to show that an unknown ester is definitely methyl ethanoate.

Answer 14

Compare with a known spectrum and if it matches

Question 15

Answer 15

yellow ppt is AgI
Ag^+ + I^- -> AgI
NaCl

Question 16

) 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.

Answer 16

Fluoride ion
AgF is soluble as no ppt forms

Question 17

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

Answer 17

white precipitate forms
Barium meal / to block x-rays
BaSO4 is completely insoluble

Question 18

Draw the displayed formula for the repeating unit of polyethene
Name this type of polymer

Answer 18

Question 19

State the meaning of the term molecular ion.

Answer 19

The molecule within one electron removed

Question 20

State why the precise relative atomic mass for the 12C isotope is exactly 12.00000

Answer 20

This is the standard reference or by the definition

Question 21

Answer 21

(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

Question 22

Which box shows for cyclohexene

Answer 22

3rd box
As there is a small peak but a peak between 1620 - 1680 cm^-1 for the C=C bond

Question 23

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.

Answer 23

Acidified K2Cr2O7
Oxidation / redox

Question 24

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.

Answer 24

Reagent = sodium carbonate
observation = effervescence

Question 25

What is formed when propanal is oxidised

Answer 25

propanoic acid

Question 26

a ketone can be an isomer of an aldehyde. State what type of isomerism is shown

Answer 26

functional group isomerism

Question 27

• skip empirical formula

Answer 27

No C=O bond at 1680 - 1750

Question 28

Reagent and observation used to test for an alcohol
- what type of alcohols does it not work for

Answer 28

Reagent : acidified potassium dichromate
observation : solution turns from orange to green
- however it does not work for tertiary alcohols

Question 29

state reagents and observations used to distinguish between
Aqueous silver nitrate and aqueous sodium nitrate

Answer 29

Reagent : HCl
Observation with silver nitrate : white ppt formed
observation with sodium nitrate : no visible change

Question 30

Answer 30

Question 31

Answer 31