Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A-level chemistry > A2 - Unit 1 - Rings, acids and amines > Flashcards

A2 - Unit 1 - Rings, acids and amines Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

What are arenes?

A

Aromatic hydrocarbons containing one or more benzene rings

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is an aromatic compound?

A

Any compound with a benzene ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What do you call a benzene ring with an NO2 group attached?

A

Nitrobenzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What do you call a benzene ring with a Br attached?

A

Bromobenzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What do you call a benzene ring with a Cl attached?

A

Chlorobenzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What do you call a benzene ring with a C2H5 group attached?

A

Ethylbenzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Give some properties of benzene on its own

A

Colourless liquid
Sweet odour
Highly flammable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Why did Kekule’s model for benzene fail to explain benzene’s low chemical reactivity?

A

If C=C double bonds were present then benzene would react in a similar way to alkenes
Each C=C would be expected to react with bromine water, decolourising it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why did Kekule’s model for benzene not match up with X ray images of benzene?

A

C=C bonds and C-C bonds have different lengths and the X ray image revealed that the molecule was symmetrical and all the bond lengths were exactly the same

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why did Kekule’s model for benzene not match up with the enthalpy change of hydrogenation?

A

The enthalpy change of hydrogenation for cyclohexane with one double bond is -120 kJ mol-1 so for benzene with three double bonds should be -360 kJ mol-1
However the actual enthalpy of hydrogenation is -208 kJ mol-1 which does not match with what was expected

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Which three factors disproved the Kekule model for benzene?

A

Bond lengths
Low reactivity
Hydrogenation of Benzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are delocalised electrons?

A

Electrons which are shared between more than two atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What features does the delocalised model of benzene have?

A

C6H6
planar hexagonal ring
trigonal planar 120degrees around each carbon atom
four outer shell electrons
three electrons bond to two carbon atoms and a hydrogen
three bonds in this plane are called sigma bonds
leaves the fourth electron in a 2p orbital above and below the plane of the carbon atoms
electron in the p orbital of carbon atom, overlaps with the electrons in the p orbitals of neighbouring carbon atoms, results in ring of electron density above and below the plane of the carbon atoms
^ produces pi bonds, not just held between carbon atoms, spread over whole ring, said to be delocalised

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Under normal conditions what does benzene not do?

A

Decolourise bromine
React with strong acid such as HCl
Reacts with halogens chlorine, bromine and iodine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is an addition reaction?

A

One in which a reactant is added to an unsaturated molecule to make a saturated molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a substitution reaction?

A

One in which an atom or group of atoms is replaced with a different atom or group of atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Why does benzene not perform any addition reactions?

A

Electrons from the delocalised system would need to bond to the atom or group of atoms resulting in the product being less stable than benzene, and the reaction would not be energetically favourable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What reaction does benzene take part in instead of addition reactions?

A

Substitution reactions
one of benzenes hydrogen atoms is replaced by another atom or group of atoms
the organic product formed retains the delocalisation and hence the stability of the benzene ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is an electrophile?

A

An atom or group of atoms that is attracted to an electron rich centre, where it accepts a pair of electrons to form a new covalent bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What specific reaction does benzene part take in?

A

Electrophilic substitution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the reagents and conditions for the nitration of benzene?

A

Concentrated HNO3
Concentrated H2SO4
50 degrees C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Give the equation for the preparation of nitrobenzene

A

C6H6 + HNO3 —-> C6H5NO2 + H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What practical is carried out when nitrating benzene?

A

Pear shaped flask
Conc nitric acid and conc sulphuric acid added while cooling the mixture in a beaker of cold water
benzene is added carefully to the nitrating mixture keeping the temp below 50 degrees
Reflux

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

When nitrating benzene for a mono-substitution reaction why do you need to ensure the temperature stays below 50 degrees?

A

Because if the mixture gets any hotter, then more than one nitro group may be substituted onto the benzene ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What can be used to make a halogen react with benzene?

A

A halogen carrier

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Give an example of a possible halogen carrier

A

AlCl3 or FeCl3 (swapping Cl for the halogen you happen to be using)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How do you carry out the halogenation of benzene?

A 
Form the electrophile:
Br2 + FeBr3 --> Br+ + FeBr4-
The electrophile reacts with benzene 
Reform the catalyst:
H+ from benzene and the FeBr4- react together making FeBr3 again and HBr
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is electrophilic substitution?

A

A type of substitution reaction in which an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is a reaction mechanism?

A

A series of steps that, together make up the overall reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is a curly arrow?

A

A symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of covalent bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What happens when bromine approaches an alkene such as cyclohexene?

A

The double bond will interact with the bromine and attach to make 1,2-dibromocyclohexane
1. The pi bond repels the electrons in the Br-Br bond
2. Induced dipole
3. One end of molecule slightly negative
Pi electron pair attracted to slightly positive bromine
4. Positively charged carbocation formed
5. Br-Br bond breaks forming Br- ion
6. Br- ions attracted towards intermediate carbocation forming covalent bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Give some properties of phenol

A

Solid at room temp
Slightly soluble in water
However presence of benzene makes phenols less soluble in water than alcohol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

When dissolved in water, what does phenol form??

A

Weak acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What happens when a reactive metal such as sodium is added to phenol?

A

The metal effervesces producing hydrogen gas

Organic salt product made

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What reaction happens when you add phenol and bromine together?

A

Electrophilic substitution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

When you add bromine to phenol where does the bromine add with regards to the OH group?

A

2,4,6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Why does bromine react more readily with phenol than benzene?

A

Lone pair of electrons on the oxygen is drawn into the phenol group and drawn into the benzene ring
Creates higher electron density and ring is activated
Increased electron density polarises bromine molecules, which are attracted more strongly towards the ring structure than in benzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Give some uses of phenol

A

Antiseptic
Synthesis of dyes
Manufacture of pharmaceuticals (e.g. Aspirin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What is the use of alkyl phenols?

A

Found in surfactants and detergents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What is the use of chlorophenols?

A

Antiseptics and disinfectants such as TCP and Dettol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What is the use for salicylic acid?

A

Preparation of aspirin and other pharmaceuticals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

What is the use for bisphenols?

A

Production of epoxy resins for paints

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

What is a functional group??

A

The part of an organic molecule responsible for its chemical reactions

44
Q

What is electronegativity?

A

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond

45
Q

What functional group do all ketones and aldehydes contain?

A

Carbonyl

C=O

46
Q

Why does a carbonyl bond not react the same as a double bond in an alkene?

A

Because the oxygen atom is more electronegative than the carbon atom
This creates a dipole in the C=O bond because the bonded electrons are attracted towards the oxygen

47
Q

What is a redox reaction?

A

A reaction in which both reduction and oxidation take place

48
Q

What is reflux?

A

The continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry

49
Q

How do you carry out the oxidation of a primary alcohols?

A

Distil with K2Cr2O7 and H2SO4 to form an aldehyde

Reflux with K2Cr2O7 and H2SO4 to form a carboxylic acid

50
Q

How do you carry out the oxidation of secondary alcohols?

A

Oxidise with K2Cr2O7 to form a ketone

51
Q

How do you oxidise an aldehyde, and how do you know when the reaction is complete?

A

Oxidise under reflux with K2Cr2O7 and the mixture will turn from orange to green

52
Q

How do you reduce an aldehyde?

A

Reduced to primary alcohols

Using NaBH4

53
Q

How do you reduce ketones?

A

Reduced to secondary alcohols

Using NaBH4

54
Q

What is a nucleophile?

A

An electron pair donor

55
Q

What is a curly arrow?

A

A symbol used in reaction mechanisms to show the movement of an electrons pair in the breaking or formation of a covalent bond

56
Q

Explain a nucleophilic addition reaction

A

Aldehydes and ketones react with NaBH4 in a nucleophilic addition reaction
BH4- ion is the source of the H- ion which acts as the nucleophile
1. electron-deficient carbon atom in the polar C=O is attacked by the H- ion
2. Lone pair of electrons from the H- forms a bond with the carbon atom
3. at the same time the pi bond in the C=O bond breaks to produce a negatively charged intermediate
4. intermediate donates an electron pair to a hydrogen atom of an H2O molecule forming a dative covalent bond and a hydroxide ion OH-
5. alcohol product

57
Q

What reagent is used to detect the presence of an aldehyde or a ketone?

A

2,4-DNP

58
Q

What is Brady’s reagent?

A

A solution of 2,4-DNP, methanol and sulphuric acid, when this solution is added to an aldehyde or a ketone a yellow or orange precipitate is formed

59
Q

How do you make Tollen’s reagent?

A

Aqueous sodium hydroxide added to silver nitrate until a brown precipitate of silver iodide is formed
Dilute aqueous ammonia is then added until the precipitate just dissolves

60
Q

What reagent can be used to distinguish between aldehydes and ketones?

A

Tollen’s reagent

61
Q

How does Tollen’s reagent help you to distinguish between aldehydes and ketones?

A

Tollen’s is a weak oxidising agent and therefore aldehydes are easily oxidised to carboxylic acid and a ‘silver mirror’ is observed
and ketones are not so no reaction is observed

62
Q

Once a carbonyl has been identified as an aldehyde or a ketone, how do you then positively identify the exact carbonyl compound?

A

Take the yellow orange solid from the test with Brady’s, filter, recrystallise to produce a purified sample of yellow or orange crystals
Filtered and allowed to dry
Melting point measured and recorded
Melting point compared to a database to identify the original aldehyde or ketone

63
Q

Which carboxylic acids are very soluble in water, and why is this?

A

Compounds with between one and four carbon atoms

Highly polar C=O and O-H allow the carboxylic acid molecules to form hydrogen bonds with water molecules

64
Q

What happens to the solubility of carboxylic acids as the number of carbon atoms in the compounds increase?

A

The solubility decreases, this is as a result of the longer non-polar hydrocarbon chain in the molecule, which does not interact with water molecules

65
Q

What are the salts formed with carboxylic acids known as?

A

Carboxylates

66
Q

Carboxylic acid + metal = ?

A

Salt and hydrogen gas

Observation: effervescence

67
Q

Carboxylic acid + base = ?

A

Salt and water

68
Q

Carboxylic acid + carbonate = ?

A

Salt + carbon dioxide + water

69
Q

What is esterification?

A

The reaction of an alcohol with a carboxylic acid to produce and ester and water

70
Q

How do you make an ester?

A

Reacting a carboxylic acid and an alcohol in the presence of an acid catalyst
or
Gently heating an acid anhydride with an alcohol (this method gives a much better yield) creating an ester and a weak acid

71
Q

What is hydrolysis?

A

A reaction with water or hydroxide ions that breaks a chemical compound into two compounds

72
Q

What reaction is the reverse of esterification?

A

Ester hydrolysis

73
Q

What happens in the acid hydrolysis of esters?

A

Ester is heated up under reflux with dilute sulphuric acid or dilute hydrochloric acid
Ester is broken down by water with the acid acting as a catalyst
Products: Weak acid + primary alcohol

74
Q

What happens in the alkaline hydrolysis of esters?

A

Aqueous sodium hydroxide is refluxed with the ester

Reaction is non-reversible and leads to the formation of the sodium salt of the carboxylic acid, and a primary alcohol

75
Q

What is the alkaline hydrolysis of esters also known as?

A

Saponification

76
Q

Is the acid hydrolysis of esters reversible or non-reversible?

A

Reversible

77
Q

Is the alkaline hydrolysis of esters reversible or non-reversible?

A

Non-reversible

78
Q

What are esters generally used for?

A

Perfumes and flavourings

79
Q

What are fatty acids made from?

A

They are esters of long-chain carboxylic acids

80
Q

What is glycerol also called?

A

Propane-1,2,3-triol

81
Q

What are mono-unsaturated fats?

A

Unsaturated fats with one double bond in the hydrocarbon chain, the double bond normally being found between carbon-9 and carbon-10

82
Q

Which two isomeric forms exist in unsaturated fats?

A

Cis and trans

83
Q

Out of both cis and trans fats, which ones increase the risk of coronary heart disease?

A

Trans-fats

84
Q

Where are the hydrogens placed in a cis configuration of an unsaturated fat?

A

They are together on the same side of the double bond

85
Q

Where are the hydrogens placed in the trans configuration of an unsaturated fat?

A

They are on opposite sides of the double bond

86
Q

In nature, which form of fatty acid is most common?

A

The cis form

87
Q

What property is a cis fatty acid at room temperature?

A

The unsaturated fatty acid molecules cannot pack closely together so cis fatty acids exist as liquids at room temperature

88
Q

What property is a trans fatty acid at room temperature?

A

The trans form of a fatty acid is quite linear in its structure so the fatty acid chains can pack together closely, this leads to a higher melting point than the cis isomer meaning it is usually solid at room temperature

89
Q

What is low density lipoprotein?

A

It is responsible for carrying cholesterol and triglycerides from the liver to the tissues

90
Q

What is high density lipoprotein?

A

Can remove cholesterol from the arteries and transport it back to the liver for excretion or re-utilisation

91
Q

Which type of lipoprotein (LDL or HDL) is known as ‘good’ lipoprotein?

A

HDL’s

LDL’s deposit lipids on the artery walls, building up fatty deposits and restricting blood flow

92
Q

How do you create biodiesel?

A

A fatty acid and methanol or ethanol
Sodium hydroxide catalyst
Glycerol is also formed and sold to the pharmaceutical or cosmetics industry
This improves the atom economy of the process

93
Q

What is the process of making biodiesel called?

A

Transesterification

94
Q

What is the difference between primary, secondary and tertiary amines?

A

Primary - only one H from ammonia is swapped out for a carbon chain
Secondary - 2 hydrogen atoms are replaced
and Tertiary - all three hydrogen atoms from ammonia are replaced

95
Q

How would you name a primary amine?

A

If there are four carbons on the alkyl chain, it is given the name butyl and the ending -amine is added as a suffix to give the name:
Butylamine

96
Q

How would you name a secondary amine?

A

The longest alkyl chain has three carbons, propyl
The suffix is added -amine
The shorter alkyl chain contains one carbon connected to the N atom so N-methyl is added as a prefix
So: N-methylpropylamine

97
Q

What properties of amines make them weak bases?

A

A lone pair of electrons on the nitrogen atom

Can accept a proton, H+

98
Q

When a base accepts a proton in an amine what happens?

A

A dative covalent bond forms between the lone pair of the nitrogen and the proton

99
Q

When you react an acid which an amine what happens?

A

It forms an ammonium salt

100
Q

How can you make aliphatic amines?

A

By warming halogenoalkanes gently with an excess of ammonia, using ethanol as a solvent

101
Q

How can nitrobenzene and other nitroarenes be reduced?

A

By using a mixture of tin and conc HCl

Heated under reflux, followed by neutralisation of the excess HCl

102
Q

What product is formed when you reduce a nitroarene?

A

An aromatic amine and water

103
Q

What are the two steps in the industrial preparation of dyestuffs?

A

Diazotisation

Coupling reactions

104
Q

What is diazotisation?

A

Phenylamine + HNO2 + 2HCl (below 10 degrees) —-> diazonium salt + 2H2O

105
Q

What is coupling?

A

Diazonium salt + phenol + NaOH

The two benzene rings are joined through the N=N functional group

A-level chemistry (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions