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A2 Chemistry > Rings, Polymers & Analysis > Flashcards

Rings, Polymers & Analysis Flashcards

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1
Q

What evidence is there against the Kekule model of benzene?

A
  • In benzene, bond lengths are all equal.
  • Benzene’s enthalpy of hydrogenation is much less negative than the Kekule structure would suggest.
  • Benzene is resistant to bromination compared to alkenes.
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2
Q

What sort or reactions does benzene undergo?

A

Electrophilic substitution.

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3
Q

What reagents are needed in the nitration of benzene to form nitrobenzene?

A

Conc nitric acid and conc sulphuric acid.

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4
Q

Write an equation for the formation of the NO2+ ion.

A

HNO3 + H2SO4 –> NO2+ + HSO4- + H2O

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5
Q

What reagents are needed in the halogenation of benzene?

A

Halogen, X2, and a halogen carrier in the solid phase, M2X3.

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6
Q

Why is benzene more resistant to bromination than alkenes?

A

Benzene has delocalised π-bonds above and below the plane of the molecule. This makes the overall electron density of the π-bond quite weak and unable to strongly polarise a Br2 molecule.
Alkenes have a localised π-bond in the C=C double bond. There is a high electron density in this region, and therefore the alkene can polarise Br2 more strongly than benzene.
Therefore, alkenes are more susceptible to electrophilic attack than benzene.

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7
Q

What is phenol?

A

Phenol is a benzene ring with an -OH group attached.

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8
Q

What is phenol’s pH?

A

Phenol is slightly acidic.

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9
Q

What does phenol form when reacted with an aqueous alkali, such as NaOH?

A

A salt with the O-Na+ and water.

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10
Q

What does phenol form when reacted with sodium metal?

A

A salt with O-Na+ and H2 (g).

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11
Q

What does phenol form when reacted with bromine water?

A

2,4,6-tribromophenol

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12
Q

What is observed when phenol is mixed with bromine water?

A

It forms a white precipitate.

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13
Q

Why does phenol undergo bromination more easily than benzene?

A

In phenol, the p-orbital electron pair in the oxygen atom in the -OH group is donated to the delocalised ring, and increases the electron density near the -OH group. This makes phenol more capable of polarising Br2 molecules than benzene, which in turn makes it undergo bromination more easily.

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14
Q

State four of the uses of phenols

A

Antiseptics, disinfectants, plastics and resins for paint.

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15
Q

What do primary alcohols oxidise to if heated gently with acidified dichromate?

A

Aldehydes.

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16
Q

What do primary alcohols oxidise to if heated under reflux with acidified dichromate?

A

Carboxylic acids.

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17
Q

What do aldehydes oxidise to if heated under reflux with acidified dichromate?

A

Carboxylic acids.

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18
Q

What do secondary alcohols oxidise to if heated under reflux with acidified dichromate?

A

Ketones.

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19
Q

Write an equation showing the oxidation of ethanol to ethanal.

A

CH3CH2OH + [O] –> CH3CHO + H2O

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20
Q

Write an equation showing the oxidation of ethanol to ethanoic acid.

A

CH3CH2OH + 2[O] –> CH3COOH + H2O

21
Q

Write an equation showing the oxidation of ethanal to ethanoic acid.

A

CH3CHO + [O] –> CH3COOH

22
Q

Write an equation showing the oxidation of propan-2-ol to propanone.

A

CH3CH(OH)CH3 + [O] –> CH3COCH3 + H2O

23
Q

What reagent can be used to reduce carbonyl compounds to form alcohols?

A

NaBH4

24
Q

By what mechanism are carbonyls reduced by the H- ion in NaBH4?

A

Nucleophilic addition.

25
Q

What can be used to test for carbonyl compounds (ketones and aldehydes)?

A

Brady’s reagent (2,4-DNPH).

26
Q

What is observed when 2,4-DNPH is added to a carbonyl compound?

A

Orange precipitate.

27
Q

How can you identify which carbonyl compound formed the orange precipitate?

A

Measure melting point of: dried, purified and recrystallized orange precipitate.

28
Q

What reagent can be added to carbonyls to identify an aldehyde?

A

Tollens’ reagent (ammoniacal silver nitrate).

29
Q

What is observed when Tollens’ reagent is heated with an aldehyde?

A

A silver mirror is formed.

30
Q

What happens to an aldehyde when Tollens’ reagent is added?

A

The aldehyde is oxidised to a carboxylic acid and silver is precipitated out.

31
Q

Why are carboxylic acids soluble in water?

A

The lone pair on the O atom forms many strong hydrogen bonds with the H atom in a water molecule. Additionally, carboxylic acids are polar and form dipole-dipole interactions with water.

32
Q

What is produced when a carboxylic acid reacts with a metal?

A

Salt + hydrogen gas

33
Q

What is produced when a carboxylic acid reacts with a carbonate?

A

salt + water + carbon dioxide

34
Q

What is produced when a carboxylic acid reacts with a base?

A

salt + water

35
Q

How can esters be produced from a carboxylic acid and an alcohol?

A

Heat carboxylic acid and alcohol under reflux with conc sulfuric acid catalyst. This reaction is reversible.

36
Q

How can esters be produced from an acid anhydride and an alcohol?

A

Warm acid anhydride with alcohol.

37
Q

What is the reaction between an ester and a dilute acid?

A

ester + water –> carboxylic acid + alcohol

38
Q

What is the reaction between an ester an a hot aqueous alkali?

A

ester + alkali –> carboxylate salt + alcohol

39
Q

State a use of esters

A

Flavourings, perfumes

40
Q

What is the systematic name of glycerol?

A

propane-1,2,3-triol

41
Q

What is cis/trans isomerism?

A

A special type of E/Z isomerism in which each carbon of the C=C double bond carries the same atom or group: the cis isomer (Z isomer) has that group on each carbon on the same side; the trans isomer (E isomer) has that group on each carbon on different sides.

42
Q

Which fats are particularly unhealthy?

A

trans-unsaturated fats and saturated fats.

43
Q

What illnesses can trans fats cause?

A

Heart attack, stroke, obesity, diabetes

44
Q

What is an amine?

A

A compound containing the -NH2 group.

45
Q

Why are amines basic?

A

The N atom in the amine group contains a lone pair of electrons which makes it able to accept a proton.

46
Q

How are aliphatic amines prepared?

A

By (substituting) reacting halogenoalkanes with excess ethanolic ammonia.

47
Q

How are aromatic amines, such as phenylamine, produced?

A

By reducing nitroarenes, such as nitrobenzene, with tin and conc HCl under reflux.

48
Q

How are diazonium ions produced from an aromatic amine?

A

React under 10*C with HNO2 (nitrous acid).

49
Q

How are azo dyes produced from the diazonium ions?

A

Coupling reaction with phenol under alkaline conditions.

A2 Chemistry (1 decks)

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