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A Level Chemistry > 3.3.9 Carboxylic Acids > Flashcards

3.3.9 Carboxylic Acids Flashcards

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 ?

A

Acid chlorides
C-Cl bond has greater electronegativity difference

20
Q

3 factors affecting how easily acylation occurs

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

A

Volatile

22
Q

Common esters

A

Fats and oils

23
Q

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

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

A

Concentrated strong acid

25
Q

What catalyst is needed for hydrolysis of esters

A

Dilute strong acid

26
Q

Base hydrolysis advantage

A

Reaction goes to completion due to neutralisation by base - more product in the mixture than acid catalysed hydrolysis

27
Q

What alcohol forms the esters that make up animal and vegetable oils

A

Glycerol

28
Q

Difference between oil and fats

A

Oils- liquid at room temp, usually unsaturated
Fats- solid at room temp, usually saturated

29
Q

How do carboxylate ions act as detergent

A

Long hydrocarbon chain of carboxylate ion mixes with grease, COO^- mixes with water

30
Q

Uses of glycerol

A

Pharmaceutical + cosmetic products
Solvent in medicine and food
Plasticisers

31
Q

Making biodiesel
Equations + conditions

A

NaOH catalyst, 60°C
Lipids + 3CH3OH —> 3 methyl esters + glycerol

32
Q

What is transesterification

A

Converting one type of ester to another

33
Q

What kind of crops is biodiesel made from

A

Rapeseed oil or soybean oil

34
Q

How is the reaction mixture of biodiesel purified and separated

A

Centrifuge
Remove remainder with water
Add acid to neutralise excess alkali catalyst
Solid soap formed

35
Q

Problems with biodiesel

A

Crops that could be used to make food are used to make fuel

36
Q

2 acid derivatives

A

Acyl chlorides
Acid anhydrides

37
Q

Name a commercially important acylation reaction

A

Manufacture of aspirin

38
Q

Conditions needed to form methyl esters from acid anhydride/acyl chloride

A

React with methanol and heat gently under reflux

39
Q

When purifying by recrystallisation, why is the minimum volume of hot solvent used

A

Saturated solution created
As many crystals will fall out of solution as possible when cooled

40
Q

Why is the solution filtered hot when purifying by recrystallisation

A

Remove insoluble impurities and ensure that the crystals don’t form in filter paper

41
Q

Why is the solution cooled in an ice bath when purifying by recrystallisation

A

Ensure as many crystals as possible fall out of solution (increase yield)

42
Q

Why are the crystals washed with cold water when purifying by recrystallisation

A

Remove soluble impurities

43
Q

Why is Büchner flask used during recrystallisation

A

Air goes through sample not just round it

44
Q

Why might percentage yield not by 100% during recrystallisation- 3 reasons

A

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
Q

Suggest why an electric heater is used rather than a Bunsen burner in this hydrolysis.

A

Many organic compounds / the ester / ethanol are flammable

46
Q

State why reflux is used in this hydrolysis.

A

Reflux allows reactant vapours (of volatile organic compounds) to be returned to the reaction mixture / does not allow any reactant vapour to escape

47
Q

Suggest why sodium benzoate is soluble in cold water but benzoic acid is insoluble in
cold water

A

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

A Level Chemistry (36 decks)

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