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A-Level Organic Chemistry AQA (Paper 2) > Carboxylic Acids And Esters > Flashcards

Carboxylic Acids And Esters Flashcards

1
Q

What is the functional group for a carboxylic acid? (3)

A
  • R-C=O (carbon bonded to OH).
  • -COOH or -CO2H.
  • Made up of a carbonyl and hydroxy, the -OH group is more acidic than the -OH group in alcohols.
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2
Q

How do you name carboxylic acids? (2)

A
  • 1). Name the alkane chain, the carbon in the carbonyl is included in the main chain and is carbon 1.
  • 2). Remove the ‘e’ and add ‘oic’ + acid.
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3
Q

How do you name carboxylic acids with a benzene ring? (2)

A
  • The suffix -carboxylic acid is used and the carbon of the functional group is not counted as part of the root.
  • Benzoic acid or benzene carboxylic acid.
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4
Q

What are the physical properties of carboxylic acids? (4)

A
  • Form hydrogen bonds with water molecules (up to butanoic acid, they are soluble in water).
  • Form hydrogen bonds with another carboxylic molecule in the solid state - have higher melting points compared to alkanes of similar relative molecular mass.
  • Dimerisation when pure.
  • Longer chains become less soluble- become more non-polar.
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5
Q

What is dimerisation?

A

•When hydrogen bonds form between compounds.

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6
Q

What is an acid?

A

•A proton donor.

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7
Q

What happens when a carboxylic acid dissociates? (3)

A
  • It forms a carboxylic acid salt/carboxylate salt and H^+ ions.
  • H^+ ions (protons) are put in a solution.
  • HA (aq) ⇌ H^+ (aq) + A^- (aq)
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8
Q

What are the factors that affect how much H^+ is in a solution for a carboxylic acid? (3)

A
  • Strong/weak- determines the position of the equilibrium, weak = low degree of dissociation, so most of the HA will remain, strong = high degree of dissociation, lots of H^+ put in the solution.
  • Degree of dissociation- how well does the carboxylic acid donate protons/how much of the reaction is happening.
  • Concentrated/dilute- how much of the carboxylic acid you put in.
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9
Q

What are carboxylic acids?

A

•Weak acids, as there is not much dissociation.

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10
Q

What is the most familiar carboxylic acid?

A

•Ethanoic acid (acetic acid), the acid in vinegar.

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11
Q

How do identify a carboxylic acid? (3)

A
  • Measure its melting point and compare it with tables of known melting points.
  • Using a Thiele tube, or the melting point can be found electronically.
  • Also, have distinct smells e.g. ethanoic acid (vinegar), butanoic acid (rancid butter), hexanoic acid (caproic acid) and octanoic acid (capryllic acid) have unpleasant smells.
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12
Q

Draw and label the structure of a carboxylic acid group polarised. (5)

A
  • R-C=O(C also bonded to OH).
  • Delta positive on C and H.
  • C^δ+ is open to attack from nucleophiles.
  • O^δ- of C=O may be attacked by positively charged species (e.g. H^+, which is protonated).
  • H^δ+ may be lost as H^+, in which the case the compound is behaving as an acid.
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13
Q

What does a carboxylic acid dissociate to form? (2)

A
  • A carboxylate salt negative ion) and H^+ ion.

* Acid puts H^+ in a solution.

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14
Q

What is the general molecular formula for carboxylic acids?

A

•CnH2n+1COOH.

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15
Q

What is the general formula for esters?

A

•RCOOR or R-C=O(carbon bonded to -O-R).

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16
Q

What is the general molecular formula for esters?

A

•RCOOR′

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17
Q

Where do esters derive from? (2)

A
  • Carboxylic acids and alcohols.
  • The hydrogen (from -OH group from the acid) is replaced by a hydrocarbon group, an alkyl or ary; group (OH replaced by OR) and water is formed.
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18
Q

How do you name esters? (2)

A
  • Alcohol (alkyl or aryl group), then acid.

* E.g. Esters from ethanoic acid are ethanoates.

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19
Q

What are the properties and uses of short chain esters? (4)

A
  • Fairly volatile.
  • Pleasant fruity smells - used in flavourings and perfumes.
  • Solvents.
  • Plasticisers.
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20
Q

What are fats and oils (lipids)?

A

•Esters with longer carbon chains.

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21
Q

What does the delocalisation (negative charge shared over the whole carboxylate group) result in? (2)

A
  • Makes the ion more stable.

* Negative charge stabilises the carbonyl group.

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22
Q

Since carboxylic acids are weak acids, where is the equilibrium?

A

•LHS.

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23
Q

What is the word and symbol equation for the reaction between ethanoic acid and sodium hydrogencarbonate? (2)

A

Ethanoic acid + sodium hydrogencarbonate —> sodium ethanoate + water + carbon dioxide
CH3COOH(aq) + NaHCO3(aq) —> CH3COONa(aq) + H2O(l) + CO2(g)

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24
Q

What is the word and symbol equation for the reaction between ethanoic acid and aqueous sodium hydroxide? (2)

A

Ethanoic acid + sodium hydroxide —> sodium ethanoate + water
CH3COOH(aq) + NaOH(aq) —> CH3COONa(aq) + H2O(l)

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25
Q

What is the word and symbol equation for the reaction between ethanoic acid and aqueous sodium carbonate? (2)

A

Ethanoic acid + sodium carbonate —> sodium ehtanoate + water + carbon dioxide
2CH3COOH(aq) + Na2CO3(aq) —> 2CH3COONa(aq) + H2O(l) + CO2(g)

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26
Q

How are esters formed?

A

•Reversible reaction between carboxylic acids and alcohols to form an equilibrium mixture of reactants and products.

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27
Q

How is the process of esterification sped up?

A

By using a strong acid catalyst.

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28
Q

What is the word equation for the reaction between ethanoic acid and ethanol?

A

Ethanoic acid + ethanol ⇌(H^+ catalyst) ethyl ethanoate + water

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29
Q

What is the opposite of esterification?

A

•Ester hydrolysis.

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30
Q

Describe the hydrolysis of esters. (2)

A
  • The carbonyl carbon atom of an ester has a 𝛿^+ charge, so it is attacked by water acting as a weak nucleophile.
  • Occurs at room temperature when a strong acid catalyst is used.
31
Q

What is the basic word equation for ester hydrolysis?

A

Ester + H2O ⇌(H^+ catalyst) carboxylic acid + alcohol

32
Q

What does the hydrolysis of esters produce? (2)

A
  • An equilibrium mixture containing the ester, water, acid and alcohol.
  • Acid is a catalyst - only affects the rate at which equilibrium is reached, not the equilibrium mixture composition.
33
Q

What can also catalyse the hydrolysis of esters? (4)

A

•Bases - the salt of the acid is produced instead of the acid itself.
•Removes the acid from the reaction mixture, so an equilibrium is not established and the reaction goes to completion.
•There is more product in the mixture:
Ester + H2O ⇌(H^+ catalyst) carboxylic acid + alcohol –(base)–> acid salt + water

34
Q

What is the mechanism of base hydrolysis?

A

•(See card).

35
Q

What are animal and vegetable oils and fats?

A

•Esters of the alcohol propane-1,2,3-triol (glycerol).

36
Q

What is the difference between fats and oils? (2)

A
  • Oils = liquid at room temperature.

* Fats = solid at room temperature.

37
Q

What do the three long-chain (12-18 carbons) molecules of carboxylic acids oils and fats contain?

A

•Fatty acids - based on glycerol they are known as triglycerides.

38
Q

When fats and oils are hydrolysed, what is produced?

A

•A mixture of glycerol and the component fatty acids.

39
Q

How can fats and oils also be hydrolysed? (saponification) (2)

A
  • By boiling with sodium hydroxide (alkali).

* Produces glycerol and a mixture of sodium salts of the three acids that formed part of the ester.

40
Q

What are the sodium salts produced by the hydrolysis of esters?

A

•Soaps.

41
Q

What is saponification?

A

•If ester hydrolysis is carried out in the presence of alkali, the carboxylic acid formed reacts with the alkali to form a carboxylate salt.

42
Q

Write a word equation for saponification.

A

Ester (RCOOR’) + alkali (OH^-) —> carboxylate ion (RCO^-) + alcohol (R’OH)

43
Q

What are the sodium salts from saponification dissociated to form? (5)

A
  • Na^+ and RCOO^-
  • RCOO^- has two distinct ends - a long hydrocarbon chain which is non-polar and the COO^- group which is polar and ionic.
  • Hydrocarbon will mix with grease (hydrophobic).
  • COO^- mixes with water (hydrophilic).
  • These salts allow grease and water to mix and be used as cleaning agents by creating a micelle - hydrophilic head on outside as it’s soluble in water and hydrophobic tail on the inside, making dirt soluble.
44
Q

What is glycerol made up of?

A

•Has three O-H bonds that readily form hydrogen bonds and is very soluble in water.

45
Q

What is glycerol used for? (4)

A
  • Pharmaceutical and cosmetic preparations - it attracts water, so it is used to prevent ointments and creams from drying out.
  • Solvent in many medicines and present in toothpastes.
  • Solvent in the food industry e.g. food colourings.
  • To plasticise various materials e.g. sheets and gaskets, cellophane and quality papers.
46
Q

How do plasticisers work? (2)

A
  • They are introduced between the molecules of the polymer which make up the material.
  • By allowing the molecules to slip over each other, the material becomes more flexible and smooth.
47
Q

What is PVC made up of?

A

•50% plasticiser e.g. esters of hexanedioic acid.

48
Q

Over time, what happens to plasticisers?

A

•They leak away, leaving the plastic brittle and inflexible.

49
Q

What is biodiesel?

A

•A renewable fuel made from oils derived from crops e.g. rapeseed.

50
Q

What is rape seed oil?

A

•A triglyceride ester.

51
Q

How do you make biodiesel? (transesterification) (2)

A
  • Rape seed oil (vegetable oil) is reacted with methanol, with a strong alkali as a catalyst.
  • Forms a mixture of methyl esters.
52
Q

What can the methyl esters be used for? (2)

A
  • A fuel in diesel vehicles with little or no modification.

* Process being introduced commercially.

53
Q

What can the strong acid and basic catalyst for transesterification be? (2)

A
  • Acid = H2SO4 or H3PO4.

* Base = NaOH or KOH.

54
Q

What is an advantage of using biodiesel over diesel?

A

•It’s renewable and carbon neutral.

55
Q

What is a disadvantage of using biodiesel over diesel?

A

•Large areas of land needed to make the vegetable oil (increase prices of other crops and deforestation).

56
Q

What is acylation?

A

•The process where an acyl group is introduced into another molecule.

57
Q

What is the acyl group?

A

•R-C=O.

58
Q

What are acid derivatives? (2)

A
  • They have the acyl group as part of their structure: R-C=O (C-Z)
  • Carbonyl group is polar.
59
Q

What are the two important acid derivatives?

A

•Acid/acyl chlorides and acid anhydrides (also esters).

60
Q

What is the general formula of an acid/acyl chloride?

A

•RCOCl.

61
Q

What is the general formula of an acid anhydride?

A

•RCOOCOR’.

62
Q

Since the carbonyl group of an acid derivative is polarised, what does that mean? (2)

A
  • It is attacked by nucleophiles at C^𝛿+ =, in the process the nucleophile replaces Z.
  • Nucleophile acquires an acyl group and is acylated.
63
Q

What are the factors that affect how readily acylation occurs? (3)

A
  • 1). The magnitude of the 𝛿+ charge on the carbonyl carbon, which depends on the electron-releasing or attracting power of Z.
  • 2). How easily Z is lost (leaving group).
  • 3). How good the nucleophile is.
64
Q

Why are acyl chlorides and acid anhydrides good acylating agents?

A

•The Z groups withdraw electrons from the carbonyl carbons, making the carbon more positive and these compounds react towards nucleophiles.

65
Q

Acyl chlorides are…

A

•More reactive than acid anhydrides.

66
Q

What are the advantages of using ethanoic anhydride instead of ethanoyl chloride as an acylating agent? (5)

A
  • It is cheaper.
  • It is less corrosive.
  • It does not react with water as readily.
  • It is safer - the by-product of its reaction is ethanoic acid (weak acid), rather than hydrogen chloride fumes.
  • Used in the production of aspirin.
67
Q

What is the systematic name of aspirin?

A

•2-ethanoyloxybenzenecarboxylic acid.

68
Q

Write the overall equation for the oxidation of a primary alcohol to an aldehyde.

A

R-CH2(OH) + [O] —-> R-CHO + H2O

69
Q

Write the overall equation for the oxidation of an aldehyde to a carboxylic acid.

A

R-CHO + [O] —-> R-COOH

70
Q

Write the overall for the oxidation of a primary alcohol to a carboxylic acid.

A

R-CH2(OH) + 2[O] —-> R-COOH + H2O

71
Q

Write the overall equation for the oxidation of a secondary alcohol to a ketone.

A

RR’CHOH + [O] —-> RCOR’ + H2O

72
Q

What are the products of acylation? (4)

A
  • Carboxylic acid (from water).
  • Ester (from alcohols).
  • Amide (from ammonia), has secondary reaction.
  • N-substituted amide (from amines), has secondary reaction.
73
Q

What is the mechanism for acylation?

A

•Nucleophilic addition-elimination.

74
Q

How do you name dicarboxylic acids?

A

•Alkyl + dioc acid e.g. butanedioc acid.

A-Level Organic Chemistry AQA (Paper 2) (17 decks)

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