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Biological Sciences Foundation Year > Carboxylic Acids and Derivatives > Flashcards

Carboxylic Acids and Derivatives Flashcards

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1
Q

Describe the solubility of small carboxylic acids in water.

A

Small carboxylic acids (up to C4) dissolve in water in all proportions due to their ability to hydrogen bond with water molecules.

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2
Q

How does the solubility of carboxylic acids change with increasing carbon chain length?

A

The solubility of carboxylic acids rapidly reduces after C4, as larger acids are less able to hydrogen bond with water.

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3
Q

Define the acidity of carboxylic acids in water.

A

Carboxylic acids are weak acids in water, only slightly dissociating, but they can displace carbon dioxide from carbonates.

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4
Q

Explain the role of delocalisation in carboxylic acid salts.

A

Delocalisation stabilises carboxylic acid salts, making their dissociation more likely and resulting in equal C-O bond lengths.

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5
Q

How does increasing chain length affect the strength of carboxylic acids?

A

Increasing chain length pushes electron density onto the COO- ion, making it more negative and less stable, which decreases the acid’s strength.

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6
Q

What effect do alkyl groups have on carboxylic acid strength?

A

Alkyl groups are electron-releasing, which can decrease the stability of the COO- ion, making the acid less strong.

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7
Q

How do electronegative chlorine atoms influence carboxylic acid strength?

A

Electronegative chlorine atoms withdraw electron density from the COO- ion, making it less negative and more stable, which increases the acid’s strength.

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8
Q

Compare the acidity of propanoic acid and ethanoic acid.

A

Propanoic acid is less acidic than ethanoic acid due to the effects of chain length on stability.

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9
Q

Compare the acidity of chloroethanoic acid and ethanoic acid.

A

Chloroethanoic acid is more acidic than ethanoic acid because the chlorine atom withdraws electron density, increasing stability.

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10
Q

Define the naming convention for carboxylic acids.

A

Carboxylic acids are named with the ending ‘-oic acid’, and no number is necessary for the acid group as it is always at the end of the chain.

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11
Q

What is the naming convention for carboxylic acids with groups on both ends of the chain?

A

Carboxylic acids with groups on both ends of the chain are called ‘-dioic acids’.

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12
Q

Provide an example of a carboxylic acid and its name.

A

Propan-1-oic acid is an example of a carboxylic acid.

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13
Q

What is the significance of the ‘e’ in the name ethanedioic acid?

A

The ‘e’ in ethanedioic acid indicates the presence of carboxylic acid groups on both ends of the carbon chain.

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14
Q

Describe the process of esterification.

A

Esterification is the reaction between carboxylic acids and alcohols in the presence of a strong acid catalyst, resulting in the formation of esters and water.

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15
Q

Define the components of an ester name.

A

An ester name consists of two parts: the part ending in –yl comes from the alcohol, and the part ending in –anoate comes from the carboxylic acid.

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16
Q

How does the esterification reaction proceed?

A

The reaction proceeds as follows: carboxylic acid + alcohol ⇌ ester + water, and it is reversible.

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17
Q

What conditions are required for the esterification reaction?

A

The esterification reaction requires heating under reflux, often for several hours or days, and the presence of an acid catalyst, such as H2SO4.

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18
Q

Explain the yield of the esterification reaction.

A

The yield of the esterification reaction is typically low, around 50%.

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19
Q

What are the characteristics of esters used in perfumes?

A

Esters used in perfumes need to be non-toxic, soluble in solvents like ethanol, volatile, and not reactive with water.

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20
Q

List some uses of esters.

A

Esters are used in perfumes, flavorings, solvents for polar organic substances, and as plasticizers for polymers.

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21
Q

How do esters behave as solvents?

A

Esters can act as solvents for polar organic substances, but they do not form hydrogen bonds due to the absence of hydrogen bonded to a highly electronegative atom.

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22
Q

What is the boiling point of esters compared to their parent carboxylic acids?

A

Esters have a lower boiling point than the hydrogen-bonded carboxylic acids from which they are derived.

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23
Q

Describe the oxidation of methanoic acid.

A

Methanoic acid can be oxidized, unlike other carboxylic acids, due to its structure containing an aldehyde group, forming carbonic acid (H2CO3), which can decompose to give CO2.

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24
Q

What happens when carboxylic acids react with metals?

A

When carboxylic acids react with metals, they form salts and release hydrogen gas.

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25
Explain the reaction of carboxylic acids with alkalis.
Carboxylic acids react with alkalis to form salts and water.
26
What is the result of carboxylic acids reacting with carbonates?
Carboxylic acids react with carbonates to form salts, water, and carbon dioxide.
27
How do plasticizers affect polymers?
Plasticizers increase the flexibility of polymers by allowing the polymer chains to move more easily over each other.
28
Describe the hydrolysis of esters with acid.
Esters can be hydrolysed by heating with dilute acid (HCl) under reflux, resulting in the formation of a carboxylic acid and an alcohol. This reaction is reversible and does not yield a good amount of products.
29
What are the products of ester hydrolysis with acid?
The products of ester hydrolysis with acid are a carboxylic acid and an alcohol.
30
Define the conditions required for ester hydrolysis with sodium hydroxide.
Ester hydrolysis with sodium hydroxide requires heating under reflux with dilute sodium hydroxide.
31
How does the hydrolysis of esters with sodium hydroxide differ from that with acid?
The hydrolysis of esters with sodium hydroxide goes to completion and is not reversible, while hydrolysis with acid is reversible and yields less product.
32
Explain the significance of using excess sodium hydroxide in ester hydrolysis.
Using excess sodium hydroxide ensures that the ester is completely hydrolysed, leading to a more complete reaction.
33
What happens to the carboxylic acid salt produced in sodium hydroxide hydrolysis?
The carboxylic acid salt produced is the anion of the carboxylic acid, which is resistant to attack by weak nucleophiles, making the reaction irreversible.
34
Describe the practical method for hydrolysing ethyl benzoate.
To hydrolyse ethyl benzoate, heat it with sodium hydroxide under reflux for 30 minutes, then cool the mixture and add hydrochloric acid to produce a precipitate of benzoic acid.
35
What is the result of adding hydrochloric acid to sodium benzoate after hydrolysis?
Adding hydrochloric acid to sodium benzoate produces benzoic acid and sodium chloride.
36
How can benzoic acid be purified after hydrolysis?
Benzoic acid can be purified using the steps outlined in practical guide AQA required practical 10 for the purification of an organic solid.
37
Explain why sodium benzoate is soluble in water while benzoic acid is not.
Sodium benzoate is ionic and soluble in water, whereas benzoic acid is not soluble due to its molecular structure.
38
Define fats and oils in terms of their chemical structure.
Fats and oils are esters of glycerol and long chain carboxylic acids (fatty acids).
39
Describe the process of hydrolysis of fats and its products.
Hydrolysis of fats produces soap, glycerol, and long chain carboxylic (fatty) acids.
40
Explain the role of long chain carboxylic acids in soap formation.
Long chain carboxylic (fatty) acids produced by the hydrolysis of fats act as soaps, with a polar hydrophilic end that mixes with water and a non-polar hydrophobic chain that mixes with grease.
41
How does glycerol interact with water?
Glycerol forms hydrogen bonds easily and is readily soluble in water.
42
List some common uses of glycerol.
Glycerol is used in cosmetics, food, and in glues.
43
Describe the process of converting vegetable oils into biodiesel.
Vegetable oils can be converted into biodiesel by reacting with methanol in the presence of a strong alkali catalyst.
44
What is biodiesel composed of?
Biodiesel is a mixture of methyl esters of long chain carboxylic acids.
45
Discuss the carbon neutrality of biodiesel production.
Biodiesel produced from plants is considered carbon-neutral because the carbon dioxide released when burned was previously absorbed by the plants during photosynthesis.
46
What factors can affect the carbon neutrality of biodiesel?
The carbon neutrality of biodiesel can be affected by the energy needed for irrigation, oil extraction, heating the reaction, and processing the fuel if fossil fuels are used.
47
Identify a potential issue related to biodiesel production and food supply.
Biodiesel production can impact the availability of land for food production.
48
Describe the main difference in by-products between acyl chlorides and acid anhydrides during reactions.
Acyl chlorides primarily produce HCl as a by-product, while acid anhydrides produce RCOOH.
49
Define the reactivity of acyl chlorides compared to carboxylic acids.
Acyl chlorides are much more reactive than carboxylic acids due to the presence of good leaving groups.
50
How do acyl chlorides react with water?
Acyl chlorides react with water to form carboxylic acids and HCl at room temperature.
51
What is the observation when acyl chlorides react with water?
The reaction produces steamy white fumes of HCl.
52
Explain the change in functional group when an acid anhydride reacts with water.
An acid anhydride reacts with water to form carboxylic acids.
53
What is the result of the reaction between acyl chlorides and alcohol?
The reaction produces esters and HCl at room temperature.
54
How do acid anhydrides react with alcohol?
Acid anhydrides react with alcohol to form esters and carboxylic acids at room temperature.
55
Describe the advantage of using acyl chlorides over carboxylic acids for ester formation.
Using acyl chlorides for ester formation is advantageous because the reaction is quicker and not reversible.
56
What is the general mechanism involved in the reactions of acyl chlorides and acid anhydrides?
The reactions involve a nucleophilic addition-elimination mechanism.
57
How does the reactivity of acid anhydrides compare to that of acyl chlorides?
Acid anhydrides have similar reactivity to acyl chlorides but are generally less reactive.
58
What are the conditions required for the reactions of acyl chlorides and acid anhydrides with water and alcohol?
The reactions occur at room temperature.
59
Illustrate the reaction of ethanoyl chloride with water.
CH3COCl + H2O → CH3COOH + HCl (g)
60
Describe the change in functional group when acyl chloride reacts with ammonia.
The acyl chloride changes to a primary amide.
61
What reagent is used in the reaction of acyl chloride to form a primary amide?
Ammonia is the reagent used.
62
Identify the conditions required for the reaction of acid anhydride with ammonia.
The reaction occurs at room temperature.
63
How does the reaction of acyl chloride with primary amines differ from that with ammonia?
The reaction with primary amines produces a secondary amide instead of a primary amide.
64
What is the observation when acyl chloride reacts with ammonia?
White smoke of NH4Cl is given off.
65
Define the mechanism involved in the reactions of acyl chlorides and acid anhydrides with amines.
The mechanism involved is nucleophilic addition-elimination.
66
Explain the product formed when CH3COCl reacts with 2NH3.
The product formed is CH3CONH2 (a primary amide) and NH4Cl.
67
What is the product of the reaction between acid anhydride and primary amine?
The product is a secondary amide.
68
How does the reaction of CH3COCl with 2CH3NH2 proceed?
It produces RCONHCH3 (a secondary amide), CH3NH3, and Cl-.
69
What is the significance of room temperature in these reactions?
Room temperature is the condition under which these reactions typically occur.
70
Describe the change in functional group when acid anhydride reacts with ammonia.
The acid anhydride changes to a primary amide.
71
What is the role of ammonia in the reactions described?
Ammonia acts as a nucleophile that reacts with acyl chlorides and acid anhydrides.
72
Identify the product formed when CH3COOCCOCH3 reacts with 2NH3.
The product formed is N-methylethanamide.
73
What happens to the acyl chloride when it reacts with a primary amine?
It forms a secondary amide.
74
Explain the significance of the white smoke observed during the reaction with ammonia.
The white smoke indicates the formation of solid NH4Cl.
75
Describe the first step in the recrystallisation process.
Dissolve the impure compound in a minimum volume of hot solvent, which should dissolve both the compound and impurities when hot, while the compound itself does not dissolve well when cold.
76
Explain the purpose of using a hot filter in the recrystallisation process.
Hot filtering quickly removes insoluble impurities and prevents crystals from reforming during the filtration process.
77
How does cooling the filtered solution affect the crystallisation process?
Cooling the filtered solution allows crystals to reform while soluble impurities remain in solution, increasing the yield of crystals.
78
What is the function of a Buchner flask in the recrystallisation process?
A Buchner flask, connected to a water pump, reduces pressure and speeds up the filtration process to separate out crystals.
79
Why is it important to wash the crystals with distilled water?
Washing the crystals with distilled water removes any remaining soluble impurities.
80
What is the final step in the recrystallisation process?
Dry the crystals between absorbent paper to remove any residual moisture.
81
Identify some reasons for loss of yield during recrystallisation.
Loss of yield can occur due to crystals being lost during filtering or washing, some product remaining in solution after recrystallisation, and other side reactions occurring.
82
Define the role of ethanoic anhydride in the synthesis of aspirin.
Ethanoic anhydride is used to convert the phenol group in 2-hydroxybenzoic acid into an ester, and it is preferred over acid chlorides for being cheaper, less corrosive, and safer to use.
83
Describe the appearance of crystals formed through recrystallisation compared to impure crystals.
The crystals formed through recrystallisation may appear as larger, needle-like crystals that are lighter in color than the impure crystals.
84
What is the significance of using a minimum volume of solvent in recrystallisation?
Using a minimum volume of solvent helps to obtain a saturated solution, which is essential for effective crystallisation upon cooling.
85
Describe the relationship between sample purity and melting point.
A very pure sample will have a sharp melting point, matching the value quoted in data books.
86
How can the degree of purity of a sample be tested?
The degree of purity can be tested by determining the melting point or melting range of the sample.
87
What is required for the heating oil used in melting point determination?
The heating oil must have a boiling point higher than the sample's melting point and low flammability.
88
Explain the setup for measuring melting point using a capillary tube.
A small amount of the sample is placed in a capillary tube, which is strapped to a thermometer immersed in heating oil.
89
What happens to the melting point if impurities are present in the sample?
If impurities are present, the melting point will be lowered and the sample will melt over a range of several degrees Celsius.
90
How can errors occur when measuring melting point?
Errors may occur if the temperature on the thermometer does not match the temperature in the actual sample tube.
91
What equipment can be used to measure melting point?
Melting point can be measured using an electronic melting point machine or a practical setup with a thermometer and capillary tube.
92
Define the melting point in the context of purity testing.
The melting point is the temperature at which a solid becomes a liquid, and it is used to assess the purity of a sample.
93
What is the procedure for heating the sample in a melting point determination?
The sample is heated slowly near the melting point to accurately determine when it begins to melt.

Biological Sciences Foundation Year (17 decks)

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