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A LEVEL - Chemistry (Both) > Topic 6b - Organic Chemistry I > Flashcards

Topic 6b - Organic Chemistry I Flashcards

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1
Q

What is a polymer?

A

A long molecule made up of repeating small units called monomers.

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2
Q

What is addition polymerisation?

A

When small molecules with double bonds (usually alkenes) add to each other and join in long chains to form polymers.

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3
Q

In addition polymerisation, what are the alkenes called?

A

Monomers

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4
Q

What is the polymer of ethene called?

A

Poly(ethene)

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5
Q

Describe how addition polymerisation works.

A
  • Several alkene monomers line up side by side
  • The C=C bond in each splits to become a C-C bond
  • This allows each monomer to join up with two adjacent monomers to create a saturated polymer
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6
Q

How can an addition polymer be shown without drawing out the whole chain?

A
  • Just draw out the repeat unit with bonds to the adjacent units.
  • Put brackets around the repeat unit, with the brackets going through the side bonds

(See pg 88 of revision guide)

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7
Q

Remember to revise drawing out addition polymers.

A

Pg 88 of revision guide

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8
Q

In addition polymerisation, how can you find the repeat unit from a monomer?

A
  • Change the C=C into a C-C bond

* Add a single bond on the outside of each carbon

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9
Q

In addition polymerisation, how can you find the monomer used to make an addition polymer?

A
  • Take the repeat unit
  • Add a C=C bond between the carbons
  • Remove the single bonds from the ends
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10
Q

What are the main ways of disposing of polymers?

A
  • Burying
  • Reusing
  • Burning
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11
Q

When is plastic waste buried in landfill?

A

When it is:
• Difficult to separate from other waste
• Not in sufficient quantities to make separation financially worthwhile
• Too difficult technically to recycle

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12
Q

Before a waste plastic can be reuse, what must be done to it?

A

It must be sorted into different types.

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13
Q

How can plastics be sorted before being reused?

A

Infrared spectroscopy

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14
Q

What are two ways in which plastics can be reused?

A
  • Remoulding -> The plastics are recycled by melting and remoulding to give new objects
  • Cracking into monomers -> These can be used as an organic feedstock to make more plastics and other chemicals
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15
Q

When are waste plastics burned?

A

When recycling isn’t possible for whatever reason and landfill isn’t an ideal option.

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16
Q

When waste plastics are burned, what is the generated heat used for?

A

Generating electricity.

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17
Q

What is the problem with burning waste plastics?

A

It produces toxic gases that must be controlled.

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18
Q

Give an example of a toxic gas produced when waste plastics are burned.

A

HCl -> Made when polymers that contain chlorine (e.g. PVC) are burned

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19
Q

How can the burning of waste plastics be controlled to reduce toxic gases?

A
  • Neutralising in scrubbers -> Waste gases are passed through scrubbers which neutralise gases, such as HCl, by reacting them with a base
  • Sorting plastics -> The plastics can be sorted before burning to remove any materials that will produce toxic gases.
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20
Q

Remember to revise the flowchart on polymer disposal.

A

Pg 88 of revision guide.

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21
Q

Name the principles used by chemists when they design a sustainable polymer manufacturing process.

A
  • Use reactant molecules that are as safe and environmentally friendly as possible
  • Use as few other materials, like solvents, as possible -> If you have to, then choose ones that won’t harm the environment
  • Use renewable materials where possible
  • Minimise energy use -> Use catalysts
  • Limit waste products, especially those hazardous to human health and the environment
  • Ensure the lifespan of the polymer is appropriate for its use
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22
Q

What are biodegradable polymers?

A

Polymers that naturally decompose by being digested by organisms.

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23
Q

What are biodegradable polymers made from?

A

• Renewable raw materials (e.g. starch from maize and other plants)
OR
• Oil fractions (e.g. the hydrocarbon isoprene)

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24
Q

What are some advantages of using renewable raw materials to make biodegradable polymers?

A
  • Raw materials aren’t going to run out like oil
  • Biodegradable polymers from plants are carbon neutral, while oil-based polymers are not
  • Some plant-based polymers may save energy over their ‘lifetime’ compared to oil-based plastics
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25
Q

Will biodegradable polymers always decompose quickly?

A

No, they still need the right conditions.

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26
Q

What are the problems of biodegradable polymers?

A
  • Must be separated out from non-biodegradable polymers before they can decompose
  • At the moment, more expensive than non-biodegradable polymers
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27
Q

What is a halogenoalkane?

A

An alkane with at least one halogen atom in place of a hydrogen atom.

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28
Q

Practise naming the halogenoalkanes on pg 90 of the revision guide.

A

Do it!

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29
Q

What are the different types of halogenoalkane?

A
  • Primary
  • Secondary
  • Tertiary
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30
Q

What is a primary halogenoalkane?

A

When the carbon with the halogen attached has:
• Two hydrogen atoms
• One alkyl group

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31
Q

What is a secondary halogenoalkane?

A

When the carbon with the halogen attached has:
• One hydrogen atom
• Two alkyl groups

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32
Q

What is a tertiary halogenoalkane?

A

When the carbon with the halogen attached has:
• No hydrogen atoms
• Three alkyl groups

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33
Q

How can an alcohol be made from a halogenoalkane?

A

EITHER:
• Reacting with water
• Reacting with aqeuous potassium hydroxide (KOH)

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34
Q

Give the general equation for the reaction of a halogenoalkane with water.

A

R-X + H2O -> R-OH + H+ + X-

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35
Q

CH3CH2Br + H2O ->

A

CH3CH2Br + H2o -> C2H5OH + H+ + Br-

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36
Q

What type of reaction is adding water to a halogenoalkane to make an alcohol?

A

Hydrolysis

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37
Q

Describe an experiment to compare the reactivity of various halogenoalkanes.

A

1) Set up three test tubes, each containing 1cm3 ethanol (as a solvent) and a couple of drops of a different halogenoalkane in each tube.
2) Stand the tubes in a water bath for 10 minutes at 60*C. Warm some silver nitrate solution in the same water bath.
3) Add 5cm3 silver nitrate solution (containing water) to each tube.
4) Time how long it takes for each test tube to form a precipitate. Note the colour too.
5) The quicker the precipitate forms, the faster the rate of hydrolysis for that halogenoalkane.

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38
Q

In the experiment to compare the reactivity of various halogenoalkanes, why is ethanol used?

A

As a solvent, so the organic and aqueous reactants can mix and react.

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39
Q

In the experiment to compare the reactivity of various halogenoalkanes, why is silver nitrate solution used?

A
  • Provides water for the hydrolysis of the alcohol.

* Silver ions react with the halide ions to give a coloured precipitate.

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40
Q

Explain how the experiment to compare the reactivity of various halogenoalkanes works.

A

• Ethanol acts as a solvent, allowing the halogenoalkane and silver nitrate solution to mix
• Water in the silver nitrate solution reacts with the halogenoalkane to give an alcohol, releasing halide ions:
R-X + H2O -> R-OH + H+ + X-
• Silver ions react with the halide ions to give a precipitate:
Ag+ (aq) + X- (aq) -> AgX (s)
• How quickly this precipitate forms reflects the reactivity of that halogenoalkane

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41
Q

What colour is silver chloride precipitate?

A

White

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42
Q

What colour is silver bromide precipitate?

A

Cream

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43
Q

What colour is silver iodide precipitate?

A

Yellow

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44
Q

Compare the reactivity of primary, secondary and tertiary halogenoalkanes.

A

Tertiary are the most reactive.

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45
Q

Compare the reactivity of chloroalkanes, bromoalkanes and iodoalkanes.

A

Iodoalkanes are the most reactive.

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46
Q

Explain the rate of hydrolysis of chloroalkanes, bromoalkanes and iodoalkanes.

A
  • In order to hydrolyse a halogenoalkane, you have to break the carbon-halogen bond.
  • How quickly this happens depends on the enthalpy of the carbon-halogen bond.
  • The larger the halogen, the longer the bond, so the lower the enthalpy -> So it is hydrolysed faster.
  • Therefore, since iodine is the largest, iodoalkanes are the most reactive.
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47
Q

When doing experiments to work out the order of reactivity of halogenoalkanes, what must you remember to do?

A
  • Change only one factor at a time.
  • For example, if you are investigating the effect of the halogen atom, remember to use all primary, all secondary or all tertiary halogenoalkanes.
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48
Q

What are the 3 ways in which halogenoalkanes can be made?

A
  • From alkanes -> Reacting with a halide in UV light -> Free radical substitution
  • From alkenes -> Reacting with hydrogen halides
  • From alcohols -> Reacting with phosphorus halides or hydrogen halides
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49
Q

By what mechanism do halogenoalkanes usually react?

A

Nucleophilic substitution

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50
Q

Why do halogenoalkanes usually react with a nucleophilic substitution mechanism?

A
  • Halogens are more electronegative than carbon
  • So the carbon-halogen bond is polar (unlike in alkanes)
  • The d+ carbon doesn’t have enough eletrons and can be attacked by a nucleophile -> OH-, NH3, CN-
  • The nucleophile can bond with the d+ carbon, while releasing the halogen
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51
Q

What things do halogenoalkanes react with?

A
  • Aqeuous potassium hydroxide (KOH)
  • Ethanolic potassium cyanide
  • Ethanolic ammonia
  • Ethanolic potassium hydroxide (KOH) -> Elimination!
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52
Q

What are some nucleophiles that can react with halogenoalkanes in nucleophilic substitution?

A
  • OH- from KOH
  • CN- from KCN
  • NH3
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53
Q

Describe the reaction mechanism for nucleophilic substitution in a halogenoalkane.

A

1) Carbon-halogen bond is polar -> d+ on the carbon and d- on the halogen
2) Nucleophile attracted to C d+ -> Arrow from lone pair to carbon
3) Carbon-halogen bond breaks heterolytically -> Arrow from the bond to the d- halogen
4) Nucleophile is now bonded to the carbon and halogen is free with a negative charge

(NOTE: This is all a one-step mechanism)

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54
Q

Give the general equation for a reaction of a halogenoalkane with aqueous potassium hydroxide.
(Conditions?)

A

R-X + KOH -> ROH + KX

Conditions: Warm KOH + Heating under reflux

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55
Q

Under what conditions can aqueous potassium hydroxide react with a halogenoalkane to give an alcohol?

A
  • Warm KOH

* Heating under reflux

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56
Q

Describe the reaction mechanism fro a halogenoalkane reacting with aqueous potassium hydroxide.

A

Mechanism: Nucleophilic substitution

1) Carbon-hydrogen bond is polar -> d+ on the carbon, d- on the halogen
2) OH- is attracted to the C d+ -> Arrow from the lone pair on the OH- to the C d+
3) Carbon-hydrogen bond breaks heterolytically -> Arrow from the bond to the d- halogen
4) Nucleophile is now bonded to the carbon (making an alcohol) and halogen is free with a negative charge

(NOTE: This is all a one-step mechanism - see pg 92 of revision guide)

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57
Q

Water or aqueous potassium hydroxide can be used to react with a halogenoalkane to make an alcohol. Compare the two in terms of rate of reaction, products and conditions.

A 
WITH H2O:
• Slower, since water is a worse nucleophile
• Makes alcohol, H+ and X-
• No specific conditions
WITH KOH (aq):
• Faster, since OH- is a better nucleophile 
• Makes alcohol and KX
• Warm KOH + Heating under reflux
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58
Q

How can a nitrile be formed from a halogenoalkane?

A

Reacting with potassium cyanide in ethanol under reflux.

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59
Q

What is formed when a halogenoalkane reacts with cyanide ions?

A
  • Nitrile

* Halide ion

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60
Q

Give the general equation for a halogenoalkane reacting with cyanide ions.
(Conditions?)

A

R-X + CN- -> R-C≡N + X-

Conditions: In ethanol + Heating under reflux

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61
Q

Under what conditions can a halogenoalkane react with potassium cyanide to give a nitrile.

A
  • KCN in ethanol

* Heating under reflux

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62
Q

Describe the reaction mechanism for a halogenoalkane reacting with ethanolic potassium cyanide.

A

Mechanism: Nucleophilic substitution

1) Carbon-hydrogen bond is polar -> d+ on the carbon, d- on the halogen
2) CN- is attracted to the C d+ -> Arrow from the lone pair on the CN- to the C d+
3) Carbon-hydrogen bond breaks heterolytically -> Arrow from the bond to the d- halogen
4) Nucleophile is now bonded to the carbon (making a nitrile) and halogen is free with a negative charge

(NOTE: This is all a one-step mechanism - see pg 92 of revision guide)

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63
Q

In a CN- ion, is the lone pair on the C or the N?

A

C

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64
Q

When is the reaction between a halogenoalane and cyandie ions useful?

A

When you need to increase the length of the carbon chain during synthesis.

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65
Q

What are amines?

A

Organic compounds based on ammonia (NH3), where one or more of the hydrogens have been replaced by an alkyl group.

(See pg 93 of revision guide)

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66
Q

How can an amine be formed from a halogenoalkane?

A

Warming with ammonia in ethanol.

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67
Q

What is ethanolic ammonia?

A

Ammonia dissolved in ethanol.

68
Q

Give the general equation for a halogenoalkane reacting with ammonia.
(Conditions?)

A

Reaction 1: R-X + NH3 -> RNH3 + X-
Reaction 2: RNH3 + NH3 -> RNH2 + NH4+
Conditions: Ethanolic ammonia + Warming

69
Q

When a halogenoalkane reacts with ammonia, what type of amine is formed?

A

Primary

70
Q

How can an amine be identified?

A

Often have a fishy smell.

71
Q

Describe the reaction mechanism for a halogenoalkane reacting with ethanolic ammonia.

A

Mechanism: Nucleophilic substitution
Reaction 1:
1) Carbon-hydrogen bond is polar -> d+ on the carbon, d- on the halogen
2) NH3 is attracted to the C d+ -> Arrow from the lone pair on the NH3 to the C d+
3) Carbon-hydrogen bond breaks heterolytically -> Arrow from the bond to the d- halogen
4) Nucleophile is now bonded to the carbon and halogen is free with a negative charge -> Nitrogen has a positive charge due to extra H bonded to it
Reaction 2:
1) Second ammonia molecule moves in -> Lone pair attracted to H on the N+
2) Arrow from the lone pair on the NH3 to the H on the N+
3) Nitrogen-hydrogen bond breaks heterolytically -> Arrow from the bond to the N+
4) This leaves an amine and an ammonium ion, as the hydrogen is lost and joins onto the ammonia

(NOTE: This is a two-step mechanism - see pg 93 of revision guide)

72
Q

Under what conditions can a halogenoalkane react with ammonia to give an amine?

A

Warming with ethanolic ammonia.

73
Q

How can an alkene be made from a halogenoalkane?

A

Reacting with potassium hydroxide in ethanol under reflux.

74
Q

Give the general equation for a halogenoalkane reacting with ethanolic potassium hydroxide.
(Conditions?)

A

Halogenoalkane + KOH -> Alkene + H2O + KBr

Conditions: Ethanolic KOH + Heating under reflux

75
Q

Under what conditions can a halogenoalkane react with ethanolic potassium hydroxide to give an alkene.

A
  • Ethanolic KOH

* Heating under reflux

76
Q

What type of reaction is a halogenoalkane reacting with ethanolic potassium hydroxide to give an alkene?

A

Elimination

77
Q

In an elimination reaction of a halogenoalkane to give an alkene, is only one product possible?

A

No, more than one isomer can be formed.

78
Q

How does the elimination reaction of a halogenoalkane to give an alkene work?

A

OH- ions from the ethanolic KOH act as a base to remove an H+ ion from the halogenoalkane.

79
Q 
Give the product when a halogenoalkane reacts with:
• Water
• Aqueous potassium hydroxide
• Potassium cyanide
• Ammonia
• Ethanolic potassium hydroxide
A
  • Water -> Alcohol (+ H+ + X-)
  • Aqueous potassium hydroxide -> Alcohol (+ KX)
  • Potassium cyanide -> Nitrile (+ X-)
  • Ammonia -> Amine (+ X- + NH4+) (2 reactions)
  • Ethanolic potassium hydroxide -> Alkene (+ H2O + KBr)
80
Q

What is the general formula for alcohols?

A

CnH2n+1OH

81
Q

What are the different types of alcohol?

A
  • Primary
  • Secondary
  • Tertiary
82
Q

What is a primary alcohol?

A

When the carbon with the OH attached has:
• Two hydrogen atoms
• One alkyl group

83
Q

What is a secondary alcohol?

A

When the carbon with the OH attached has:
• One hydrogen atom
• Two alkyl groups

84
Q

What is a tertiary alcohol?

A

When the carbon with the OH attached has:
• No hydrogen atoms
• Three alkyl groups

85
Q

What reactions can alcohols undergo?

A
  • Substitution -> To halogenoalkanes
  • Dehydration
  • Oxidation (/Combustion)
86
Q

How can a chloroalkane be produced from an alcohol?

A

Reacting with PCl5 or HCl.

87
Q

What is produced when an alcohol reacts with phosphorus pentachloride (PCl5)?

A
  • Chloroalkane
  • Hydrochloric acid
  • POCl3
88
Q

Give the general equation for an alcohol reacting with phosphorus pentachloride (PCl5).

A

ROH + PCl5 -> RCl + HCl + POCl3

89
Q

What is produced when an alcohol reacts with hydrochloric acid?

A
  • Chloroalkane

* Water

90
Q

Give the general equation for an alcohol reacting with hydrochloric acid.

A

ROH + HCl -> RCl + H2O

91
Q

(CH3)3COH + HCl ->

A

(CH3)3COH + HCl -> (CH3)3CCl + H2O

92
Q

How does the structure of an alcohol relate to the rate of reaction when reacting with HCl?

A

Tertiary alcohol is fastest.

Primary alcohol is slowest.

93
Q

How can a bromoalkane be produced from an alcohol?

A

Reacting with compounds containing bromide ions (usually HBr) with an acid catalyst.

94
Q

Give an example of a compound that an alcohol could react with to produce a bromoalkane.

A 
Potassium bromide (KBr)
(With an acid catalyst e.g. H2SO4)
95
Q

Describe how 2-bromo-2-methylpropane could be produced from:
• 2-methylpropan-2-ol
• Potassium bromide
• 50% concentrated sulfuric acid

A

1) First, potassium bromide reacts with sulfuric acid to form hydrogen bromide.
2) Then, the HBr reacts with the alcohol to form a bromoalkane and water.

(See pg 94 of revision guide)

96
Q

How can an iodoalkane be produced from an alcohol?

A

Refluxing with red phsphorus and iodine.

97
Q

Describe how an iodoalkane can be produced from:
• Alcohol
• Red phosphorus
• Iodine

A

1) Red phosphorus and iodine react to give phosphorus triiodide (PI3) by refluxing
2) Alcohol reacts with PI3 to give halogenoalkane

(See pg 94 of revision guide)

98
Q

What is produced when an alcohol reacts with HBr?

A
  • Bromoalkane

* Water

99
Q

What is produced when an alcohol reacts with PI3?

A
  • Iodoalkane

* H3PO3

100
Q

Give the general equation for an alcohol reacting with phosphorus triiodide.

A

3ROH + PI3 -> 3RI + H3PO3

101
Q

Producing an iodoalkane from an alcohol requires reacting it with phosphorus triiodide (PI3). How is this PI3 obtained?

A

It is usually produced ‘in situ’ (in the reaction mixture) by refluxing red phosphorus and iodine.

102
Q

How can the different halogenoalkanes be produced from an alcohol?

A
  • Chloroalkane -> Reacting with PCl5 or HCl
  • Bromoalkane -> Reacting with a compound containing bromide ions, in the presence of an acid catalyst
  • Iodoalkanes -> Reacting with red phosphorus and iodine
103
Q

What catalyst in required to produce a bromoalkane from an alcohol?

A

Acid catalyst (e.g. H2SO4)

104
Q

What is the type of reaction by which an alcohol is converted into a halogenoalkane?

A
  • Substitution

* Because the OH is replaced by the halogen atom

105
Q

What is a dehydration reation?

A

An elimination reaction where water is eliminated.

106
Q

How can an alkene be produced from an alcohol?

A

Heating with an acid catalyst, which dehydrates the alcohol.

107
Q

What type of reaction is producing an alkene from an alcohol?

A

Dehydration (a type of elimination reaction)

108
Q

Give an example of the catalyst used in converting alcohols to alkenes.

A

Concentrated phosphoric acid (H3PO4)

109
Q

Give the equation for ethanol being dehydrated.

Conditions?

A

C2H5OH -> CH2=CH2 + H2O

Conditions: Heating with a phosphoric acid acid catalyst

110
Q

Describe how dehydration of an alcohol works.

A

An OH and a H are removed from two adjacent C atoms. This gives a H2O molecule and a double C=C bond.

111
Q

In the dehydration of an alcohol, how many resulting alkenes are possible?

A
  • Two -> Since the H must be removed from an adjacent C atom, the double bond can form in two places
  • Howver, each of these may have E/Z isomers

(See pg 95 of revision guide)

112
Q

What happens if the dehydration of an alcohol can produce more than one possible alkene?

A

There will be a mixture of the resulting products.

113
Q

When butan-2-ol is heated to 170*C with concentrated phosphoric acid, it dehydrates to form a mixture of products. Give the names and structures of all the organic compounds in the mixture.

A
  • Elimnation can occur between the OH group and he H on either carbon-1 or carbon-2.
  • This results in two possible alkene products - but-1-ene and but-2-ene, but but-2-ene can form E/Z isomers.
  • Therefore, products: But-1-ene, E-But-2-ene, Z-But-2-ene
114
Q

Remember to revise the dehydration of alcohols.

A

Pg 95 of revision guide.

115
Q

What is the simplest way to oxidise alcohols?

A

Burn them.

116
Q

What are the products of complete alcohol combustion?

A
  • Carbon dioxide

* Water

117
Q

C2H5OH (l) + 3O2 (g) ->

A

C2H5OH (l) + 3O2 (g) -> 2CO2 (g) + 3H2O (g)

118
Q

What determines how much an alcohol can be oxidised?

A

Whether it is primary, secondary or tertiary.

119
Q

What is used to mildly oxidise alcohols?

A

Acidified sodium/potassium dichromate(VI)

120
Q

How is acidified dichromate(VI) symbolised?

A

Cr2O7 2- / H+

121
Q

What colour is the dichromate(VI) ion?

A

Orange

122
Q

What happens to the orange dichromate(VI) ion in oxidation of alcohols?

A

It is reduced to the green chromium(III) ion.

123
Q

What colour change can be observed when an alcohol is oxidised? Why?

A
  • From orange to green.

* Orange dichromate(VI) ions in the reducing agent are being reduced to green chromium(III) ions.

124
Q

What are primary alcohols oxidised to?

A

Aldehydes, then carboxylic acids.

125
Q

What are secondary alcohols oxidised to?

A

Ketones.

126
Q

What are tertiary alcohols oxidised to?

A

They can’t be oxidised, except by burning.

127
Q

What is a carbonyl group?

A

A C=O functional group.

128
Q

Give two examples of carbonyl compounds.

A
  • Aldehydes

* Ketones

129
Q

What are the two most similar of aldehydes, ketones and carboxylic acids? Why?

A

Aldehydes and ketones - they have the same molecular formula, but the C=O bond is on a different carbon.

130
Q

How can you recognise an aldehyde from a diagram?

A
  • -CHO functional group
  • End carbon has a single bond with hydrogen and double bond with carbon

(See diagram pg 96 of revision guide)

131
Q

How can you recognise a ketone from a diagram?

A
  • -C=O functional group
  • Non-end carbon has a double bond with oxygen and single bonds with adjacent carbons

(See diagram pg 96 of revision guide)

132
Q

How do you recognise a carboxylic acid from a diagram?

A
  • -COOH functional group
  • End carbon has a single bond with an OH group and a double bond with an oxygen

(See diagram pg 96 of revision guide)

133
Q

What is the difference between an aldehyde and ketone?

A
  • Aldehyde -> Hydrogen and one alkyl group attached to carbonyl carbon atom
  • Ketone -> Two alkyl groups attached to carbonyl carbon atom
134
Q

What is the general formula for aldehydes?

A

CnH2nO

135
Q

What is the general formula for ketones?

A

CnH2nO

136
Q

In terms of oxidation of alcohols, what is oxidation?

A

Loss of a hydrogen atom from the carbon which the OH is attached to.

137
Q

Name: CH3CH2CHO

A

Propanal

138
Q

Name: CH3COCH3

A

Propanone

139
Q

What test can be done to tell apart aldehydes and ketones?

A
  • Heating with Fehling’s / Benedict’s solution
  • Aldehyde -> Solution turns brick-red
  • Ketone -> Solution remains blue
140
Q

Describe how the Fehling’s/Benedict’s test works.

A
  • The Fehling’s/Benedict’s solution contains blue copper(II) ions
  • Aldehyde can be further oxidised to a carboxylic acid -> Reduces copper ions to copper(I) oxide precipitate
  • Ketone cannot be oxidised -> Solution remains blue

(Note: A carboxylic would give no colour change either, since it can’t be easily oxidised - CHECK!)

141
Q

Why can either the Fehling’s or Benedict’s solution be used in the test for aldehydes and ketones?

A

Both contain copper(II) ions that can be reduced to give the colour change.

142
Q

Why can primary alcohols be oxidised more than secondary and tertiary alcohols?

A
  • In alcohols, oxidation is the loss of hydrogen from the carbon to which the OH is attached
  • Therefore, primary alcohols have two H atoms to lose to form aldehydes that can be oxidised again
  • Secondary alcohols have only 1, so they form ketones that can’t be oxidised
  • Tertiary alcohols have no H to lose in the first place
143
Q

Remember to practise drawing out the oxidation of a primary alcohol.

A

Diagram pg 96 of revision guide.

144
Q

How is an oxidising agent shown in reactions?

A

[O]

145
Q

In oxidising a primary alcohol to an aldehyde, how many hydrogens are lost from the alcohol?

A

2

146
Q

In oxidising an aldehyde to a carboxylic acid, how many hydrogens are lost from the aldehyde?

A

None - it just gains an oxygen.

147
Q

When a primary alcohol is oxidised partially, what is produced apart from an aldehyde?

A

Water

148
Q

CH3CH2CH2OH + [O] ->

A

CH3CH2CH2OH + [O] -> CH3CH2CHO + H2O

149
Q

How can you control whether an aldehyde or a carboxylic acid will be produced by the oxidation of a primary alcohol?

A

Controlling the conditions.

150
Q

What smell is given off by ethanal (an aldehyde)?

A

Apple smell.

151
Q

What smell is given off by ethanoic acid?

A

Vinegar smell.

152
Q

How can you ensure that the oxidation of a primary alcohol produces an aldehyde?

A
  • Set up distillation equipment.
  • Gently heat excess alcohol with a controlled amount of the oxidising agent (acidified potassium dichromate(VI)).
  • Distill the aldehyde off as it forms.

(See pg 220 of textbook)

153
Q

Why does the distillation method to obtain an aldehyde from alcohol oxidation work?

A

The aldehyde has a lower boiling point than the alcohol, so it can easily be distilled off as soon as it forms.

154
Q

How can you ensure that the oxidation of a primary alcohol produces a carboxylic acid?

A
  • Set up reflux equipment.
  • Vigorously reflux controlled amount of the alcohol with excess oxidising agent (acidified potassium dichromate(VI)).
  • Set up distillation equipment.
  • Distill off about 3cm3 of the product.

(See pg 220 of textbook)

155
Q

Remember to practise drawing out the oxidation of a secondary alcohol.

A

Pg 97 of revision guide.

156
Q

Describe how you can oxidise a secondary alcohol to produce a ketone.

A

Reflux the alcohol with excess oxidising agent (acidified potassium dichromate(VI)).

157
Q

In oxidising a secondary alcohol to a ketone, how many hydrogens are lost from the alcohol?

A

2

158
Q

When an aldehyde is oxidised, what is produced apart from a carboxylic acid?

A

Nothing

159
Q

When a secondary alcohol is oxidised partially, what is produced apart from a ketone?

A

Water

160
Q

CH3CH2CHO + [O] ->

A

CH3CH2CHO + [O] -> CH3CH2COOH

161
Q

What happens when a tertiary alcohol is heated with acidified potassium dichromate(VI) solution?

A

The solution stays orange (since tertiary alcohols can’t easily be oxidised).

162
Q

What is the only way to oxidise tertiary alcohols?

A

Burning them.

163
Q

What are the two tests involved in alcohols and what is each used for?

A
  • Benedict’s/Fehling’s -> Used to test for aldehydes and ketones -> Colour change indicates aldehyde
  • Heating with acidified potassium dichromate(VI) -> Used to test for primary, secondary and tertiary alcohols -> Turns from orange to green with primary and secondary alcohols
164
Q

Describe how you could test for primary, secondary and tertiary alcohols.

A

1st TEST:
• Heat the sample gently with acidified potassium dichromate(VI)
• If the solution turns green -> The alcohol is primary or secondary -> Go to test 2
• If the solution remains orange -> The alcohol is tertiary -> No need for test 2
2nd TEST:
• Heat the product of the first test with Fehling’s / Benedict’s solution
• Solution turns brick-red -> Indicates aldehyde -> Therefore, alcohol is primary
• Solution remains blue -> Indicates ketone -> Therefore, alcohol is secondary

165
Q

REMEMBER TO ADD FLASHCARDS ON PGS 98-99!

A

DO IT!

A LEVEL - Chemistry (Both) (21 decks)

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