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LGS OCR A-Level Chemistry A > Module 6 - Organic Chemistry & Analysis - Exam Questions > Flashcards

Module 6 - Organic Chemistry & Analysis - Exam Questions Flashcards

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1
Q

What does the symbol [H] represent? (1)

A

Reducing agent

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2
Q

Suggest a reagent that would convert the -OH group in phenol to an -O(-) group (1)

A

NaOH (sodium hydroxide) takes the H from phenol

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3
Q

Explain what is meant by the term 1,4-diamino (2)

A

Diamino: two amine groups

1,4: Their position on the ring

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4
Q

1,4-dinitrobenzene is converted to 1,4-diaminobenzene, what type of reaction is this? (1)

A

Reduction

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5
Q

State reagents and conditions required to convert 1,4-dinitrobenzene to 1,4-diaminobenzene (2)

A

Tin and HCl

Conc acid under reflux

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6
Q

Explain how the amino groups in a primary amine allow the molecule to act as a base (2)

A

Accepts H+ using the lone pair on N

Which forms a dative covalent bond

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7
Q

State whether you would expect hexane-1,6-diamine to be a stronger or weaker base than 1,4-diaminobenzene. Explain your reasoning (3)

A

Hexane-1,6-diamine is a stronger base because:
Electrons move towards the N in hexane-1,6-diamine
Lone pair from N is partially delocalised around the ring in diaminobenzene
So electron pair is more easily donated

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8
Q

Suggest possible problems of making a chiral drug such as salbutamol and describe two
ways that the pharmaceutical industry might overcome these problems (4)

A 
Production of a single isomer is more expensive
One of the isomers is more active
Overcome by using:
Enzyme catalyst
Chiral catalyst
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9
Q

Explain what is meant by an α-amino acid (1)

A

Both NH2 and COOH are joined to the same C

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10
Q

Explain the evidence that led scientists to doubt the model proposed by Kekulé (3)

A

Bond length intermediate between/different from (short) C=C and (long) C–C
ΔH hydrogenation less exothermic than expected
Only reacts with Br2 at high temp or in presence of a halogen carrier

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11
Q

The chemist observed that bromine decolourises when it reacts with phenol
What other observation would she have made? (1)

A

White precipitate

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12
Q

Cyclohexene also decolourises bromine

Name the organic product formed (1)

A

1,2-Dibromocyclohexane

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13
Q

Explain the relative resistance to bromination of benzene compared to phenol and compared to cyclohexene (5)

A 
Benzene - π bonds are delocalised
Phenol - a lone pair of electrons on the OH is partially delocalised into the ring
Cyclohexene - electrons are localised
Benzene has a lower electron density
Benzene cannot induce a dipole in Br2
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14
Q

State the general formula of an α-amino acid (1)

A

C bonded to NH2, COOH, H and R

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15
Q

The mixture of tripeptides can be analysed by using gas chromatography, coupled with mass spectrometry. Summarise how each method contributes to the analysis (3)

A

Gas chromatograph separates the tripeptides
Mass spectrometer produces a distinctive fragmentation pattern
Identification by computer using a spectral database

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16
Q

State what is meant by the term zwitterion (1)

A

Ion has both + and - charges

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17
Q

What is meant by the term stereoisomer? (1)

A

Molecules with the same structure but different arrangements in space

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18
Q

How does cis-trans isomerism arise in organic molecules? (1)

A

Double bond does not rotate

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19
Q

State a use for Kevlar (1)

A

Bullet proof clothing

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20
Q

Kevlar is formed from a diamine and a dioic acid, what kind of polymerisation is this reaction? (1)

A

Condensation`

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21
Q

Chlorobenzene can be nitrated to form a mixture of products. Suggest why the reaction forms a mixture of products (1)

A

Nitration at different positions on the ring

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22
Q

State what the biochemist would see when hydroxyethanal reacts with
Tollens’ reagent (1)

A

Silver mirror

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23
Q

The biochemist also reacted hydroxyethanal with acidified dichromate by heating
under reflux. Write an equation for this oxidation. [O] is oxidising agent (2)

A

HOCH2CHO + 3[O] -> HOOCCOOH + H2O

24
Q

The biochemist then reduced hydroxyethanal using aqueous NaBH4.
Write the structural formula of the organic product (1)

A

HOCH2CH2OH

25
Q

What is meant by the term nucleophile? (1)

A

Electron pair donor

26
Q

Describe a simple chemical test that would show that but-2-enal is an aldehyde (2)

A

Heat with Tollens’ reagent

Gives a silver mirror

27
Q

Explain why Tollens’ reagent test gives a different result for aldehydes and ketones (1)

A

Aldehydes can reduce Ag+ to Ag

28
Q

Tollens’ reagent can be used to identify the aldehyde group in cinnamaldehyde. (6)
• Describe how you would make Tollens’ reagent and carry out this test in the
laboratory.
• Explain what happens to both the Tollens’ reagent and the cinnamaldehyde in
this reaction.

A 
Method:
Silver nitrate
Ammonia
Heat
Silver mirror forms
Explanation:
Silver ions reduced
Aldehyde oxidised to a carboxylic acid
29
Q

How does gas chromatography separate the compounds in the mixture? (1)

A

Relative solubility in stationary phase

30
Q

Two compounds pass through a gas chromatogram, what is suggested about the one that comes out first? (1)

A

Less soluble in the stationary phase

31
Q 
Three compounds:
Ketone & primary alcohol (A),
Aldehyde & secondary alcohol (B),
Ketone & tertiary alcohol (C)
Describe chemical tests to distinguish between the compounds (4)
A

First react all with Tollens’ reagent, silver mirror forms with compound B
B + [O] -> carboxylic acid
Then react A and C with acidified potassium dichromate, colour change for A
A + 2[O] -> carboxylic acid and water

32
Q

An alcohol is reacted with excess K2Cr2O7/H2SO4 under reflux, state observation during reaction? (1)

A

Colour changes from orange to green

33
Q

Describe a chemical test that you could use to detect the presence of a carbonyl group in an organic compound, reagent and observation (2)

A

2,4-DNPH

Orange precipitate

34
Q

State one possible health risk of a diet that is high in trans oils (1)

A

Heart disease

35
Q

A chemical with chiral centres can be synthesised from naturally occuring steroids. Suggest an advantage of having a synthetic route (1)

A

Ensures correct chirality

36
Q

Explain what is meant by the term condensation polymerisation (1)

A

Monomers form polymer and a small molecule i.e H2O

37
Q

Before any skin cream can be sold to the public, it must be tested to ensure it is safe to
use. Suggest why (1)

A

To test for adverse side effects

38
Q

Methylglyoxal, CH3COCHO, is formed in the body during metabolism.
Describe one reduction reaction and one oxidation reaction of methylglyoxal that could be carried out in the laboratory.
Include reagents, equations and observations (5)

A

Methylglyoxal is reduced by NaBH4
CH3COCHO + 4[H] -> CH3CHOHCH2OH
Methylglyoxal is oxidised by H2SO4 and K2Cr2O7, turns green
CH3COCHO + [O] -> CH3COCOOH

39
Q

A synthetic polymer can be easily hydrolysed compared with other synthetic polymers, explain why it is thought polymers such as this one are better for the environment (1)

A

Biodegradable, whereas hydrocarbon based polymers are not

40
Q 
Explain how the student could use infrared spectroscopy to confirm which compound is a
carboxylic acid (1)
A

Peak in range 2500-3300

41
Q

The aldehyde has the molecular formula C5H10O.
The 1H NMR spectrum of the aldehyde contains a doublet at δ = 0.9 ppm with a relative peak area of six compared with the aldehyde proton.
Analyse this information to deduce the structure of the aldehyde. Explain your reasoning (3)

A

Relative peak area indicates 2 x CH3 in the same environment

(CH3)2CH-CH2-CHO

42
Q

State what is meant by retention time (1)

A

The time from the injection of the sample for the component to leave the column

43
Q

How could a specific carbonyl be identified not using spectroscopy after reaction with 2,4-DNPH? (2)

A

Take melting point of orange crystals

Compare melting point with known values

44
Q

Outline purification (4)

A

Recrystallisation
Dissolve impure solid in minimum volume of hot water
Cool solution and filter solid
Wash with cold water and dry

45
Q

Phenol undergoes easier nitration than benzoic acid, explain this (3)

A

Lone pair of OH partially delocalises into ring
COOH is an electron withdrawing group
Phenol has greater electron density in the ring and so is more susceptible to attack

46
Q

Suggest why a polyester is biodegradable (1)

A

Ester bond can be hydrolysed

47
Q

A CHO based molecule is slightly acidic but has no visible change when Na2CO3 is added, suggest the functional group responsible (1)

A

Phenol

48
Q

Explain why phenol is nitrates more readily than benzene (3)

A

In phenol a lone pair of electrons on O is donated into π system
Electron density increases
Phenol accepts electrophile more

49
Q

Explain what is meant by molecular ion peak (1)

A

Peak caused by unfragmented molecule

50
Q

Explain what is meant by base peak (1)

A

Peak with the greatest relative intensity

51
Q

Name the process by which TLC separates α-amino acids (1)

A

Adsorption

52
Q

A student used TLC to separate three different α-amino acids, explain how the student could analyse the chromatogram to identify the α-amino acids present (2)

A

Calculate the Rf value

Compare Rf values to those known for amino acids

53
Q

Several α-amino acids have structures that are very similar. Suggest why this could cause problems when using TLC to analyse mixtures of α-amino acids (1)

A

Amino acids won’t separate because similar compounds have similar Rf values

54
Q

Define Rf value (1)

A

Distance moved by a component divided by distance moved by solvent

55
Q

What are the roles of the gas and liquid in gas/liquid chromatography? (2)

A

Role of gas: Mobile phase

Role of liquid: Stationary phase

56
Q

Explain how the gas/liquid chromatogram could be used to determine the percentage composition of each component in the mixture (3)

A

Measure area under each peak
Find total area
% = area of one peak/total area (as a percentage)

LGS OCR A-Level Chemistry A (33 decks)

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