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Chemistry A - Level > Topic 17C - Carboxylic Acids > Flashcards

Topic 17C - Carboxylic Acids Flashcards

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1
Q

What is the carboxylic functional group?

A

-COOH, the carboxyl group

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2
Q

As the Carboxylic acid carbon chain length increase the boiling point…

A

Increases

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3
Q

Are the boiling points of carboxylic acids higher or lower than alcohols of a similar carbon chain length and molar mass?

A

Higher

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4
Q

Why do carboxylic acids have higher boiling points that they’re corresponding alcohols?

A

This is because carboxylic acids form stronger hydrogen bonds in comparison to alcohols. Due to the C=O electron withdrawing group, the O-H bond becomes more polarised hence forming these stronger hydrogen bonds

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5
Q

Can carboxylic acids bond with themselves? How?

A

Yes they can. Carboxylic acids can form dimers (how they usually exist in nature) by hydrogen bonds forming between them.

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6
Q

Where is methnaoic acid found in nature?

A

The irritant injected in an ant bite

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7
Q

Where is ethanedioic acid found in nature?

A

The toxic substance found in rhubarb leaves

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8
Q

Are carboxylic acids strong or weak acids?

A

Weak acids

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9
Q

What is the definition of a weak acid?

A

An acid that only partially dissociates into its ions

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10
Q

Write the equation for when a carboxylic acid, for example, methanoic acid, is mixed with water

A

HCOOH + H2O → HCOO(-) + H3O(+)

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11
Q

What is the carboxylate ion?

A

HCOO-

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12
Q

What does then carboxylate ion look like in display formula?

A

It is drawn like methanoic acid but without the H off of the O atom. The O atom therefore has a negative charge.

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13
Q

Are the Bond lengths all equal in the carboxylate ion? Why?

A

Yes the bond lengths are all equal. This is because the electrons are delocalised and are spread over the carboxylate group. You draw this by drawing the negative charge with a circle around it alongside dashed lines between the two oxygens.

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14
Q

What does the delocalisation of electrons in the carboxylate ion do?

A

It makes the carboxylate ion more stable so it is less likely to be protonated again. This makes carboxylic acids more acidic than similar molecules such as alcohols

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15
Q

How does the value of Ka, strength of the carboxylic acid, vary as you increase the carbon chain length? Why is this and how does it effect the stability of the structure?

A

As you increase the carbon chain length the Ka value decreases and the acid gets weaker. This is because as you increase the carbon chain the number of alkyl groups increases, which are electron donating. Therefore, the additional alkyl groups increase the electron density around the carboxylate group of the acid. The acid is therefore more likely to be protonated and so less stable.

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16
Q

How does the value of Ka (dissociation constant) vary as you increase the number of halogen atoms on the carboxylic acid carbon chain? Why is this and how does it effect the stability?

A

As you increase the number of halogen atoms attached to the carboxylic carbon chain the Ka value increases and the acid gets stronger. This is because Halide groups are electron withdrawing which means they further delocalise the charge of the carboxylate ion and stabilise it more

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17
Q

How do you produce a carboxylic acid from an alcohol?

A

You would react an alcohol with potassium dichromate and dilute sulphuric acid. The potassium dichromate acts as the oxidising agent in this reaction.

Alcohol + [O] → Carboxylic acid + H2O

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18
Q

What apparatus do you use to oxidise an alcohol fully to a carboxylic acid?

A

Reflux apparatus, as this heats the alcohol continually.

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19
Q

What functional group is found in nitriles?

A

C (triple bond) N

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20
Q

What are the two ways nitriles can be hydrolysed to form a carboxylic acid?

A

By a strong base or a strong acid

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21
Q

What are the reactants and conditions for the hydrolysis of nitriles with a strong base?

A
  • dilute NaOH
  • heat under reflux
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22
Q

What are the reactants and conditions for the hydrolysis of nitriles with a strong acid?

A
  • dilute HCl
  • heat under reflux
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23
Q

Write an equation for the hydrolysis of the nitrile (propanenitrile) with a strong base

A

H2O + NaOH + CH3CH2CN → CH3CH2COO-Na+ NH3

You have formed sodium propanoate not a carboxylic acid so you would need to have to acidify the final solution with a strong acid in order to protonate the oxygen

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24
Q

Write an equation for the hydrolysis of the nitrile (ethanenitrile) with a strong acid

A

2H2O + CH3CN + HCl → CH3COOH + NH4Cl

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25
Q

Why are carboxylic acids stronger acids that alcohols?

A

The C=O bond attracts O-H electrons away from the O-H bond making it easier for the bond to break and the H atom to be lost. This makes carboxylic acids stronger acids.

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26
Q

Why does the carbonyl carbon not get attacked by a nucleophile?

A

This is because there is a flow of electrons from the O in the O-H bond that is delta -. This effectively reduces the partially positive charge on the carbonyl carbon which means it is very unlikely to be attacked by a nucleophile

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27
Q

What is the general equation for an acid (carboxylic acid) + alkali reaction?

A

acid + alkali → salt + water

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28
Q

Write an equation for ethanoic acid + NaOH

A

CH3COOH + NaOH → CH3COO-Na+ + H2O

REMEMBER CARBOXYLIC ACIDS DON’T FULLY DISSOCIATE - this is why you have to write the O and Na ions

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29
Q

What is the general equation for an acid (carboxylic acid) + carbonate?

A

Acid + carbonate → salt + water + carbon dioxide

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30
Q

Write an equation for ethanoic acid + calcium carbonate?

A

2CH3COOH + CaCO3 → [CH3COO-]2Ca (2+) + H2O + CO2

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31
Q

What reaction can be used to test for carboxylic acid?

A

Acid + metal carbonate reaction as carboxylic acids are the only substance that will release carbon dioxide from the carbonate compound

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32
Q

What is the general equation for the acid + metal reaction?

A

Acid + metal → salt + hydrogen

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33
Q

Write an equation for the reaction of ethanoic acid and sodium

A

2CH3COOH + 2Na → 2CH3COO-Na+ + H2

REMEMBER CARBOXYLIC ACIDS DO NOT FULLY DISSOCIATE INTO THERE IONS

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34
Q

What are the reactants required to reduce a carboxylic acid?

A

Carboxylic acids are hard to reduce comparatively to carbonyl compounds

REACTANT
- reducing agent LiAlH4 in dry ether (if done with water present the water will react with the hydride ions in the agent)

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35
Q

Write the equation for the reduction of ethanoic acid

A

CH3COOH + 4[H] → CH3CH2OH + H2O

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36
Q

What is the Ka value?

A

it is the dissociation constant for weak acids. The higher the value of Ka, the stronger the acid

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37
Q

Which functional groups have a reaction with phosphorus pentachloride?

A

Alcohols, -OH
Carboxylic Acids, -COOH

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38
Q

Write the equation for the reaction of the carboxylic acid, ethanoic acid, with phosphorus pentachloride

A

CH3COOH + PCl5 -> CH3COCl + POCl3 + HCl

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39
Q

What does the presence of misty fumes of hydrogen chloride on addition of phosphorus pentachloride indicate?

A

That there is an -OH functional group present in the molecule

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39
Q

What organic product is produced when a carboxylic acid reacts with phosphorus pentachloride?

A

An acyl chloride, COCl

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40
Q

The reaction of alcohols with carboxylic acids is called…

A

esterification

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41
Q

What are the reagents for esterification?

A

alcohol + carboxylic acid

42
Q

Write an equation for the reaction of methanol with ethanoic acid

A

CH3COOH + CH3OH -> CHCOOCH3 + H2O

Ethanoic acid + methanol -> methyl ethanoate

43
Q

What are the conditions required to speed up the process of esterification?

A
  • Heating under reflux
  • Adding a strong acid catalyst e.g sulphuric acid
44
Q

Is esterification as slow process under normal conditions?

A

yes

45
Q

What is the main physical property of esters?

A

Their sweet smells

46
Q

When reacting an alcohol with a carboxylic acid to form an ester, why should you add sodium carbonate solution afterwards?

A

To neutralise any excess acid

47
Q

Using Le Chateliers principle, explain the three ways you can increase the yield of an ester during esterification

A
  1. By adding excess alcohol/carboxylic acid (depending on the cost) the POE would shift to the right to oppose the change, therefore increasing the yield of ester
  2. By reacting some of the water product to remove it the POE will move to the right to oppose the change and increase the water, therefore increasing the yield of ester
  3. By distilling off the ester you decrease its concentration. The POE will shift to the right to oppose the change and increase the concentration, therefore increasing the ester yield
48
Q

What is the functional group of a an acyl chloride?

A

-COCl

49
Q

Name CH3COCl

A

Ethanoyl Chloride

50
Q

Are acyl chlorides more or less reactive in comparison to carboxylic acids?

A

A lot more

51
Q

Do acyl chlorides occur naturally? Why?

A

They do not occur naturally as they are so reactive and so would immediately react with water in the environment to form the parent carboxylic acid

52
Q

Why are acyl chlorides so reactive?

A

The carbon in the C=O and C-Cl bonds has a relatively large partially positive charge due to the electron withdrawing effect of both the oxygen and chlorine atom

53
Q

What type of species are acyl chlorides attacked by?

A

nucleophiles - these attack the partially positive carbon atom

54
Q

Where do the reactions of acyl chlorides need to be carried out? Why?

A

In a fume cupboard as they react violently

55
Q

acyl chloride + water -> …

A

carboxylic acid + hydrochloric acid

56
Q

What is the equation for the reaction of ethanoyl chloride with water?

A

CH3COCl (l) + H2O (l) -> CH3COOH (l) + HCl (g)

57
Q

What would your observations be when watching the reaction of ethanoyl chloride with water?

A
  • Effervescence
  • Temperature rise - as the reaction is exothermic
  • Misty white fumes when NH3 added showing HCl had been formed
58
Q

acyl chloride + alcohol -> …

A

ester + hydrochloric acid

59
Q

What is the equation for the reaction of Ethanoyl chloride with ethanol?

A

CH3COCl + CH3CH2OH -> CH3COOCH2CH3 + HCl

60
Q

When naming the ester formed from the reaction of an acyl chloride with an alcohol which part comes first?

A

Alcohol then acyl chloride

61
Q

What would your observations be when watching the reaction of ethanoyl chloride with ethanol?

A
  • smell of sweet pear drops (ester formed)
  • Misty white fumes when NH3 added showing HCl had been formed
  • Temperature rise - as the reaction is exothermic
62
Q

acyl chloride + ammonia -> …

A

amide + ammonium chloride

63
Q

What is the functional group of an amide?

A

-CONH2

64
Q

What is the functional group of an amine?

A

-CH2NH2

65
Q

What is the equation for the reaction of Ethanoyl chloride with ammonia?

A

CH3COCl + NH3 -> CH3CONH2 + NH4Cl

66
Q

What acts as the nucleophile in the reaction of Ethanoyl chloride with ammonia?

A

NH3, as it has a lone pair of electrons

67
Q

What would your observations be when watching the reaction of ethanoyl chloride with ammonia?

A
  • A white solid of NH4Cl is formed
  • Temperature rise - as the reaction is exothermic
68
Q

What is the order of reactivity of ammonia, ethanol and water from most to least?

A

ammonia>ethanol>water

69
Q

Why is ammonia a better nucleophile in comparison to ethanol and water?

A

As the lone pair of electrons on ammonia are more readily available to form a new bond

70
Q

What is the name of the type of reaction that acyl chlorides undergo?

A

nucleophilic addition-elimination reactions

71
Q

Describe the mechanism of the addition-elimination reaction of acyl chlorides e.g ethanoyl chloride with nucleophiles (ammonia, alcohols, water), and therefore draw it

A
  • The carbon within the C=O and C-Cl bond has a large partially positive charge.
  • In the first step the nucleophile attacks the partially positive carbon. Subsequently one of the bonds from the C=O bond is broken and the pair of electrons goes to the oxygen. Curly arrows represent the movement of electrons.
  • In the second step the oxygen that gained the electrons now has a lone pair of electrons and a negative charge. The nucleophile that joined has now been given a positive charge. In this step the pair of electrons on the oxygen form the bond with the carbon again and subsequently this breaks the C-Cl bond.
  • In the third step you now have CH3CO(OH)CH3 (different with ammonia nucleophile) with a positive charge on the Oxygen atom of the -OH. The Cl- ion with a lone pair of electrons that was removed now attacks the H of the O-H bond whilst the pair of electrons in the bond go to the oxygen atom making the charge neutral again.
  • The products are CH3COOCH3 + HCl
72
Q

What are the products of the reaction of acyl chloride + amine?

A

N-substituted amide + HCl

73
Q

Write the equation for the reaction of ethanoyl chloride with methylamine

A

CH3COCl + CH3NH2 -> CH3CONHCH3 + HCl

74
Q

What happens in the reaction of an acyl chloride with an amine?

A

The chlorine is removed for the acyl chloride and this reacts with one of the hydrogen atoms

74
Q

How reactive are acyl chlorides with amines in comparison to other species (ammonia, alcohols, water)?

A

They are more reactive than any of the other nucleophiles

75
Q

Can esters form hydrogen bonds between themselves? Why?

A

No esters cannot form hydrogen bonds between themselves. This is because They have no hydrogen atom bonded to an N,O or F

75
Q

Are esters acids or bases?

A

They are neither, they are neutral

76
Q

Are esters soluble?

A

Yes, esters are soluble as they are able to form hydrogen bonds with water molecules through the oxygen atoms’ lone pair of electrons. However, the solubility of the esters drops of quickly as you increase their molar mass as it becomes energetically unfavourable for the London forces and permanent dipole-dipole forces to be broken and replaced by hydrogen bonds.

77
Q

What is the name for the reverse reaction of esterification?

A

Hydrolysis of esters

78
Q

Is esterification a reversible reaction?

A

Yes, with the correct reagents and conditions

79
Q

What are the two types of hydrolysis of esters?

A

Acid hydrolysis and Alkali hydrolysis

80
Q

What are the conditions for the hydrolysis of esters?

A

Heat under reflux

81
Q

What is the catalyst for acid hydrolysis?

A

H+ ions, dilute acids such as HCl and H2SO4

82
Q

What is the catalyst for alkali hydrolysis?

A

OH- ions, sodium hydroxide solution

83
Q

Why is the reaction of esters with pure water never used?

A

As it is so slow

84
Q

When an ester is heated under reflux with dilute acid what are the products?

A

The corresponding carboxylic acid and alcohol

85
Q

When an ester is heated under reflux with a dilute alkaline solution what are the products?

A

The corresponding carboxylate ion and alcohol

86
Q

What are the two positives of alkaline hydrolysis over acid hydrolysis?

A

The reaction isn’t reversible and it is easier to separate the products of the sodium salt and the alcohol

87
Q

What do you have to do to the carboxylate ion in order to turn it into the carboxylic acid?

A

Add a strong acid such as dilute HCl. This will flood the solution with H+ ions and once these combine with your carboxylate ions they are unlikely to break again as carboxylic acids are weak acids.

88
Q

What are the esters that make up fats and oils?

A

Esters of glycerol and fatty acids

89
Q

What is the part of fats and oils that gives it their properties?

A

The fatty acid chains, whether they are saturated or unsaturated

90
Q

Do fats have high melting points? Why?

A

Fats do have high melting points. This is because fats are mainly saturated hydrocarbons that are able to fit together neatly increasing the London Forces between them.

91
Q

Do oils have high melting points? Why?

A

Oils do not have high melting points. This is because oils have many unsaturated hydrocarbons chains. The double bonds mean that the chains are bent and do not fit well together, thereby decreasing the effect of the London Forces so less energies required to overcome them.

92
Q

What is saponification?

A

The hydrolysis of fats and oils

93
Q

Describe the process of saponification?

A

Fats and oils are essentially esters. By heating the esters with NaOH you conduct base hydrolysis. The OH- ions from the NaOH react with the fats/oils to form the carboxylate ion and an alcohol. The carboxylate ions combine with the Na+ ions to form a sodium salt (O-Na+). This sodium salt is used to produce salt.

94
Q

What household item does saponification create?

A

Soap

95
Q

What must you convert vegetable oils into in order for them to burned directly in engines?

A

Biodiesel

96
Q

What do you have to react the oils with in order to produce biodiesel? What is produced?

A

Methanol (flammable) using a strong alkali (KOH/NaOH) as a catalyst. This produces a mixture of methyl esters of fatty acids which is biodiesel.

97
Q

What are three examples of condensation polymers?

A
  • Polyesters
  • Polyamides
  • Polypeptides
98
Q

What is the definition of a condensation reaction?

A

A condensation reaction is when two molecules, normally monomers, react together and a small molecule, often water of hydrogen chloride, is eliminated.

99
Q

What two different monomers are used to make the condensation polymer, polyester?

A

Diols - these have 2 hydroxyl -OH groups attached to either end
Dicarboxylic Acid - These has 2 carboxyl -COOH groups attached to either ends

100
Q

What is the linkage for polyesters?

A

-COO-

Chemistry A - Level (26 decks)

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