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A Level Chemistry > 3.3.9 Carboxylic Acids > Flashcards

3.3.9 Carboxylic Acids Flashcards

(47 cards)

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1
Q

Esters products

A

Vegetable oils and animal fats propane-1,2,3-triol (glycerol)

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2
Q

Common uses of esters

A

Solvents, plasticisers, perfumes, food flavourings

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3
Q

Esters hydrolysed in acid/alkaline conditions to form

A

Alcohols and carboxylic acids
Salts of carboxylic acids

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4
Q

Vegetable oils and animal fats can be hydrolysed
What are the conditions + products

A

Under alkaline conditions to give salt and glycerol

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5
Q

What is biodiesel + how is it produced

A

Mixture of methyl esters of long chain carboxylic acids
Produced by reacting vegetable oils with methanol with catalyst

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6
Q

Acid anhydride

A

R-C(=O)-O-C(=O)-R

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7
Q

Acyl chloride structure

A

-COCl

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8
Q

Amide structure

A

R-C(=O)-N-(R)2

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9
Q

Advantages of ethanoic anhydride over ethanoyl chloride in manufacture of aspirin

A

Add to salicylic acid
Cheaper
Safer
Less corrosive
Reacts more slowly with water
Doesn’t produce dangerous hydrogen chloride fumes

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10
Q

After the solid benzoic acid has been filtered off, it can be purified. Describe the method that the student should use to purify the benzoic acid.

A

Dissolve crude product in hot solvent/water
of minimum volume
Filter (hot to remove insoluble impurities)
Cool to recrystallise
Filter under reduced pressure
with Buchner/Hirsch apparatus wash (with cold solvent)
dry

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11
Q

State a simple chemical test that distinguishes the propanoic acid from the propan-1-ol

A

Add sodium carbonate
Acid-bubbles
Alcohol-no visible reaction

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12
Q

Compare solubility of carboxylic acids and esters

A

Both polar
Carboxylic acids more soluble
Can form hydrogen bonds with water
Esters can’t
As chain increases, solubility decreases - polarity decreases

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13
Q

Compare the melting point of carboxylic acids and esters

A

Carboxylic acids is higher
Contains hydrogen bonding
Esters only contain Van der Waals

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14
Q

Smell of carboxylic acids and esters

A

Acids- vinegar
Esters- fruity/sweet, used in food flavourings and perfume

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15
Q

Stability of carboxylic acids

A

In the carboxylate ion, the negative charge delocalises its electrons
Stabilising the ion

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16
Q

Reaction of carboxylic acids with metal/metal carbonate

A

Metal carboxylate (salt) + hydrogen
Metal carboxylate (salt) + water + CO2

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17
Q

Reaction of carboxylic acid with base

A

Ionic salt + water
E.g. CH3COOCH3 + NaOH —>
CH3COO-Na+ + H2O

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18
Q

Reactivity of acid chlorides and anhydrides

A

Reactive
Polar bonds
Large differences in electronegativity of C-Cl and C=O

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19
Q

Are acid chlorides or acid anhydrides more reactive ?

Study These Flashcards
A

Acid chlorides
C-Cl bond has greater electronegativity difference

20
Q

3 factors affecting how easily acylation occurs

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A

Size of delta + charge on C
How easily Z is lost E.g. Cl
How good nucleophile is at donating lone pair

21
Q

Give a physical properties of an ester

22
Q

Common esters

Study These Flashcards
A

Fats and oils

23
Q

What happens to the negative charge on carboxylate ions in terms of electrons

Study These Flashcards
A

Electrons delocalised so charge is shared across whole carboxylate group

24
Q

What catalyst is needed for the formation of esters from alcohols and carboxylic acids

Study These Flashcards
A

Concentrated strong acid

25
What catalyst is needed for hydrolysis of esters
Dilute strong acid
26
Base hydrolysis advantage
Reaction goes to completion due to neutralisation by base - more product in the mixture than acid catalysed hydrolysis
27
What alcohol forms the esters that make up animal and vegetable oils
Glycerol
28
Difference between oil and fats
Oils- liquid at room temp, usually unsaturated Fats- solid at room temp, usually saturated
29
How do carboxylate ions act as detergent
Long hydrocarbon chain of carboxylate ion mixes with grease, COO^- mixes with water
30
Uses of glycerol
Pharmaceutical + cosmetic products Solvent in medicine and food Plasticisers
31
Making biodiesel Equations + conditions
NaOH catalyst, 60°C Lipids + 3CH3OH —> 3 methyl esters + glycerol
32
What is transesterification
Converting one type of ester to another
33
What kind of crops is biodiesel made from
Rapeseed oil or soybean oil
34
How is the reaction mixture of biodiesel purified and separated
Centrifuge Remove remainder with water Add acid to neutralise excess alkali catalyst Solid soap formed
35
Problems with biodiesel
Crops that could be used to make food are used to make fuel
36
2 acid derivatives
Acyl chlorides Acid anhydrides
37
Name a commercially important acylation reaction
Manufacture of aspirin
38
Conditions needed to form methyl esters from acid anhydride/acyl chloride
React with methanol and heat gently under reflux
39
When purifying by recrystallisation, why is the minimum volume of hot solvent used
Saturated solution created As many crystals will fall out of solution as possible when cooled
40
Why is the solution filtered hot when purifying by recrystallisation
Remove insoluble impurities and ensure that the crystals don’t form in filter paper
41
Why is the solution cooled in an ice bath when purifying by recrystallisation
Ensure as many crystals as possible fall out of solution (increase yield)
42
Why are the crystals washed with cold water when purifying by recrystallisation
Remove soluble impurities
43
Why is Büchner flask used during recrystallisation
Air goes through sample not just round it
44
Why might percentage yield not by 100% during recrystallisation- 3 reasons
Product lost during filtration, during, weighing Not all transferred between apparatus Product left dissolved in solution- doesn’t recrystallise Some left on filter paper Sample still wet
45
Suggest why an electric heater is used rather than a Bunsen burner in this hydrolysis.
Many organic compounds / the ester / ethanol are flammable
46
State why reflux is used in this hydrolysis.
Reflux allows reactant vapours (of volatile organic compounds) to be returned to the reaction mixture / does not allow any reactant vapour to escape
47
Suggest why sodium benzoate is soluble in cold water but benzoic acid is insoluble in cold water
Sodium benzoate soluble because it is ionic Benzoic acid insoluble because: despite the polarity of the COOH group / ability of COOH to form H-bonds, the benzene ring is non-polar

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