Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

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

Topic 17C - Carboxylic Acids Flashcards

1
Q

What is the carboxylic functional group?

A

-COOH, the carboxyl group

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

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

A

Increases

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

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

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

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

Where is methnaoic acid found in nature?

A

The irritant injected in an ant bite

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

Where is ethanedioic acid found in nature?

A

The toxic substance found in rhubarb leaves

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

Are carboxylic acids strong or weak acids?

A

Weak acids

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

What is the definition of a weak acid?

A

An acid that only partially dissociates into its ions

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

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

A

HCOOH + H2O → HCOO(-) + H3O(+)

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

What is the carboxylate ion?

A

HCOO-

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

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

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

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

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

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

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

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

What functional group is found in nitriles?

A

C (triple bond) N

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

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

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

A
  • dilute NaOH
  • heat under reflux
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

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

A
  • dilute HCl
  • heat under reflux
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

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

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

A

2H2O + CH3CN + HCl → CH3COOH + NH4Cl

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Why are carboxylic acids stronger acids that alcohols?
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.
26
Why does the carbonyl carbon not get attacked by a nucleophile?
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
27
What is the general equation for an acid (carboxylic acid) + alkali reaction?
acid + alkali → salt + water
28
Write an equation for ethanoic acid + NaOH
CH3COOH + NaOH → CH3COO-Na+ + H2O REMEMBER CARBOXYLIC ACIDS DON’T FULLY DISSOCIATE - this is why you have to write the O and Na ions
29
What is the general equation for an acid (carboxylic acid) + carbonate?
Acid + carbonate → salt + water + carbon dioxide
30
Write an equation for ethanoic acid + calcium carbonate?
2CH3COOH + CaCO3 → [CH3COO-]2Ca (2+) + H2O + CO2
31
What reaction can be used to test for carboxylic acid?
Acid + metal carbonate reaction as carboxylic acids are the only substance that will release carbon dioxide from the carbonate compound
32
What is the general equation for the acid + metal reaction?
Acid + metal → salt + hydrogen
33
Write an equation for the reaction of ethanoic acid and sodium
2CH3COOH + 2Na → 2CH3COO-Na+ + H2 REMEMBER CARBOXYLIC ACIDS DO NOT FULLY DISSOCIATE INTO THERE IONS
34
What are the reactants required to reduce a carboxylic acid?
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)
35
Write the equation for the reduction of ethanoic acid
CH3COOH + 4[H] → CH3CH2OH + H2O
36
What is the Ka value?
it is the dissociation constant for weak acids. The higher the value of Ka, the stronger the acid
37
Which functional groups have a reaction with phosphorus pentachloride?
Alcohols, -OH Carboxylic Acids, -COOH
38
Write the equation for the reaction of the carboxylic acid, ethanoic acid, with phosphorus pentachloride
CH3COOH + PCl5 -> CH3COCl + POCl3 + HCl
39
What does the presence of misty fumes of hydrogen chloride on addition of phosphorus pentachloride indicate?
That there is an -OH functional group present in the molecule
39
What organic product is produced when a carboxylic acid reacts with phosphorus pentachloride?
An acyl chloride, COCl
40
The reaction of alcohols with carboxylic acids is called...
esterification
41
What are the reagents for esterification?
alcohol + carboxylic acid
42
Write an equation for the reaction of methanol with ethanoic acid
CH3COOH + CH3OH -> CHCOOCH3 + H2O Ethanoic acid + methanol -> methyl ethanoate
43
What are the conditions required to speed up the process of esterification?
- Heating under reflux - Adding a strong acid catalyst e.g sulphuric acid
44
Is esterification as slow process under normal conditions?
yes
45
What is the main physical property of esters?
Their sweet smells
46
When reacting an alcohol with a carboxylic acid to form an ester, why should you add sodium carbonate solution afterwards?
To neutralise any excess acid
47
Using Le Chateliers principle, explain the three ways you can increase the yield of an ester during esterification
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
What is the functional group of a an acyl chloride?
-COCl
49
Name CH3COCl
Ethanoyl Chloride
50
Are acyl chlorides more or less reactive in comparison to carboxylic acids?
A lot more
51
Do acyl chlorides occur naturally? Why?
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
Why are acyl chlorides so reactive?
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
What type of species are acyl chlorides attacked by?
nucleophiles - these attack the partially positive carbon atom
54
Where do the reactions of acyl chlorides need to be carried out? Why?
In a fume cupboard as they react violently
55
acyl chloride + water -> ...
carboxylic acid + hydrochloric acid
56
What is the equation for the reaction of ethanoyl chloride with water?
CH3COCl (l) + H2O (l) -> CH3COOH (l) + HCl (g)
57
What would your observations be when watching the reaction of ethanoyl chloride with water?
- Effervescence - Temperature rise - as the reaction is exothermic - Misty white fumes when NH3 added showing HCl had been formed
58
acyl chloride + alcohol -> ...
ester + hydrochloric acid
59
What is the equation for the reaction of Ethanoyl chloride with ethanol?
CH3COCl + CH3CH2OH -> CH3COOCH2CH3 + HCl
60
When naming the ester formed from the reaction of an acyl chloride with an alcohol which part comes first?
Alcohol then acyl chloride
61
What would your observations be when watching the reaction of ethanoyl chloride with ethanol?
- 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
acyl chloride + ammonia -> ...
amide + ammonium chloride
63
What is the functional group of an amide?
-CONH2
64
What is the functional group of an amine?
-CH2NH2
65
What is the equation for the reaction of Ethanoyl chloride with ammonia?
CH3COCl + NH3 -> CH3CONH2 + NH4Cl
66
What acts as the nucleophile in the reaction of Ethanoyl chloride with ammonia?
NH3, as it has a lone pair of electrons
67
What would your observations be when watching the reaction of ethanoyl chloride with ammonia?
- A white solid of NH4Cl is formed - Temperature rise - as the reaction is exothermic
68
What is the order of reactivity of ammonia, ethanol and water from most to least?
ammonia>ethanol>water
69
Why is ammonia a better nucleophile in comparison to ethanol and water?
As the lone pair of electrons on ammonia are more readily available to form a new bond
70
What is the name of the type of reaction that acyl chlorides undergo?
nucleophilic addition-elimination reactions
71
Describe the mechanism of the addition-elimination reaction of acyl chlorides e.g ethanoyl chloride with nucleophiles (ammonia, alcohols, water), and therefore draw it
- 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
What are the products of the reaction of acyl chloride + amine?
N-substituted amide + HCl
73
Write the equation for the reaction of ethanoyl chloride with methylamine
CH3COCl + CH3NH2 -> CH3CONHCH3 + HCl
74
What happens in the reaction of an acyl chloride with an amine?
The chlorine is removed for the acyl chloride and this reacts with one of the hydrogen atoms
74
How reactive are acyl chlorides with amines in comparison to other species (ammonia, alcohols, water)?
They are more reactive than any of the other nucleophiles
75
Can esters form hydrogen bonds between themselves? Why?
No esters cannot form hydrogen bonds between themselves. This is because They have no hydrogen atom bonded to an N,O or F
75
Are esters acids or bases?
They are neither, they are neutral
76
Are esters soluble?
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
What is the name for the reverse reaction of esterification?
Hydrolysis of esters
78
Is esterification a reversible reaction?
Yes, with the correct reagents and conditions
79
What are the two types of hydrolysis of esters?
Acid hydrolysis and Alkali hydrolysis
80
What are the conditions for the hydrolysis of esters?
Heat under reflux
81
What is the catalyst for acid hydrolysis?
H+ ions, dilute acids such as HCl and H2SO4
82
What is the catalyst for alkali hydrolysis?
OH- ions, sodium hydroxide solution
83
Why is the reaction of esters with pure water never used?
As it is so slow
84
When an ester is heated under reflux with dilute acid what are the products?
The corresponding carboxylic acid and alcohol
85
When an ester is heated under reflux with a dilute alkaline solution what are the products?
The corresponding carboxylate ion and alcohol
86
What are the two positives of alkaline hydrolysis over acid hydrolysis?
The reaction isn't reversible and it is easier to separate the products of the sodium salt and the alcohol
87
What do you have to do to the carboxylate ion in order to turn it into the carboxylic acid?
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
What are the esters that make up fats and oils?
Esters of glycerol and fatty acids
89
What is the part of fats and oils that gives it their properties?
The fatty acid chains, whether they are saturated or unsaturated
90
Do fats have high melting points? Why?
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
Do oils have high melting points? Why?
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
What is saponification?
The hydrolysis of fats and oils
93
Describe the process of saponification?
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
What household item does saponification create?
Soap
95
What must you convert vegetable oils into in order for them to burned directly in engines?
Biodiesel
96
What do you have to react the oils with in order to produce biodiesel? What is produced?
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
What are three examples of condensation polymers?
- Polyesters - Polyamides - Polypeptides
98
What is the definition of a condensation reaction?
A condensation reaction is when two molecules, normally monomers, react together and a small molecule, often water of hydrogen chloride, is eliminated.
99
What two different monomers are used to make the condensation polymer, polyester?
Diols - these have 2 hydroxyl -OH groups attached to either end Dicarboxylic Acid - These has 2 carboxyl -COOH groups attached to either ends
100
What is the linkage for polyesters?
-COO-

Chemistry A - Level (26 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions