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aqa a level chemistry > Carboxylic Acids + Derivatives > Flashcards

Carboxylic Acids + Derivatives Flashcards

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1
Q

What is a carboxylic acid and it’s functional group ?

A

-COOH (C=O and C-OH)

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2
Q

How do you name carboxylic acids ?

A

Carbon chain length -oic acid.

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3
Q

Are carboxylic acids soluble in water ?

A

•Yes, acid group forms hydrogen bonds with water
•Carbon chain length affects solubility

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4
Q

What intermolecular forces are there in carboxylic acids ?

A

Hydrogen bonds and van ver waals

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5
Q

What are esters (functional group), what are they formed from ?

A

•They are formed from carboxylic acids and alcohols
•RCOOR (C=O C-O-C)

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6
Q

Write an equation for the reaction of ethanoic acid and propan-1-ol

A

CH3COOH + CH3CH2CH2OH -> CH3COOCH2CH2CH3 + H2O

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7
Q

How do you name esters ?

A

•Start with the group that replaced the H, then acid suffix
•Eg, propanol + ethanoic acid = propylethanoate

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8
Q

What characteristic physical properties do esters have ?

A

Volatile, fruity smells

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9
Q

What are the uses of esters ?

A

Flavourings, perfumes (long chain)
Solvents, plasticisers (short chain)

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10
Q

What are some common natural esters ?

A

Fats and oils

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11
Q

How are carboxylic acids polarised ?

A

C d+
Both O d-

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12
Q

Write an equilibrium formed by ethanoic acid in solution ?

A

CH3COOH -> CH3COO- + H+

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13
Q

What happens to the negative charge in an ethanoate ion in terms of electrons ?

A

Electrons become delocalised and are shared across the whole group

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14
Q

How would you distinguish carboxylic acids from other OH containing compounds ?

A

Add NaHCO3, acids will produce sodium salt, water and CO2

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15
Q

Write an equation for the reaction of ethanoic acid and sodium hydroxide

A

CH3COOH + NaOH -> CH3COONa + H2O

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16
Q

Write an equation for the reaction of ethanoic acid and NaCO3

A

2CH3COOH + Na2CO3 -> 2CH3COONa + H2O + CO2

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17
Q

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

A

Concentrated strong acid eg H2SO4

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18
Q

What catalyst is needed for the hydrolysis of esters ?

A

Dilute strong acid eg H2SO4

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19
Q

What is an alternative method of hydrolysis of esters ?

A

Base hydrolysis

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20
Q

What are the advantages of base hydrolysis of esters ?

A

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

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21
Q

Which alcohols forms the esters that make up animal and vegetable oils ?

A

Glycerol / propan-1,2,3-triol

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22
Q

What is the difference between oil and fat ?

A

Oils are liquid at room temperature fats are solids
Fats are usually saturated

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23
Q

What are the products of producing fats and oils ?

A

Propan-1,2,3-triol and sodium salts of the acids that make up the ester (hydrolysed with NaOH)

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24
Q

What are the uses of Propan-1,2,3-triol and sodium salts ?

A

Soaps and cleaning products

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25
Q

What does the long hydrocarbon chain of the carboxylate ion do ?

A

Mixes with grease (conditioner)

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26
Q

What does the COO- group do ?

A

Mixes with water

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27
Q

Why does a carboxylate ion with a long hydrocarbon chain make a good cleaning agent ?

A

Carboxylate ion mixes with the grease which can then be removed from water

28
Q

What is the IUPAC name of glycerol ?

A

Propane-1,2,3-triol

29
Q

What are some common uses of glycerol ?

A

•Used in pharmaceutical and cosmetic preparations, eg stops cream drying
•A solvent in many medicines eg toothpaste
•A solvent in the food industry eg food colourings
•Plasticisers

30
Q

How do you make biodiesel (general equation and conditions)

A

•NaOH catalyst, 60C
•Lipid + 3CH3OH -> 3 methyl esters + glycerol

31
Q

What is transesterification?

A

Converting one type of ester to another

32
Q

What kind of seed is biodiesel made from ?

A

Rapeseed oil or soybean oil

33
Q

How is the reaction mixture of biodiesel purified and separated?

A

•Setting tank or centrifuge
•Remove remainder with water
•Add acid to neutralise excess alkali catalyst
•Soap is formed, easy to remove.

34
Q

What is an issue with producing biodiesel ?

A

Crops that could be used for food are used for fuel

35
Q

What are carboxylic acid derivatives ?

A

Molecules that have an acyl group as a part of their structure, formed from carboxylic acids

36
Q

Name two carboxylic acid derivatives and give their functional groups

A

Acyl chlorides RCOCl
Acid anhydrides RCOOCR / (RCO)2O

37
Q

Draw the mechanism for the acylation of a nucleophile by an acid derivative

A

•C d+ O d- (C=O)
•Arrow from lone pair of Nu- to d+ of C, further arrow from C=O to O
•This gives O negative charge, arrow from lone pair of O to bond, further arrow from C-X to X.

38
Q

What factors effect how readily the acylation of a nucleophile by an acid derivative occurs ?

A

*Magnitude of the d+ charge on the carbonyl group (electronegativity of group being substituted)
*How easily the group being substituted is lost
*How readily the nucleophile will donate electrons.

39
Q

What effect do the Cl and O atoms in acyl chlorides/acid anhydrides have on the partial charge of the carbonyl atom ?

A

They increase the d+ charge by attracting electrons, this means that they react more readily with nucleophiles

40
Q

Which are more reactive: Acyl chlorides or acid anhydrides ?

A

Acyl chlorides

41
Q

What is the name of the mechanism by which acyl chlorides and acid anhydrides acylate nucleophiles?

A

Nucleophilic addition-elimination

42
Q

If the nucleophile is ammonia for the acylation of acyl chlorides or acid anhydrides, what are the products of the reaction ?

A

An amide

43
Q

Write an equation for the reaction of ethanoyl chloride and ammonia

A

CH3COCl + 2NH3 -> CH3CONH2 + NH4Cl

44
Q

Draw / describe the mechanism for the reaction of ethanoyl chloride and ammonia

A

*d+ on C, d- on O and Cl of ethanoyl
*Arrow from lone pair of N (NH3) to d+ C
*This produces intermediate whereby the C=O becomes C-O and NH3 joins C, there is now N+ and O-
*Arrow from lone pair of O- to C-O, arrow from C-Cl to Cl and arrow from N+-H to N+.

45
Q

If the nucleophile is a primary amide, what are the products of the acylation of acyl chlorides or acid anhydrides ?

A

N-Substituted amide

46
Q

Write an equation for the reaction of ethanoyl chloride and methylamine

A

CH3COCl + CH3NH2 -> CH3CONHCH3 + CH3NH3Cl

47
Q

Draw / describe the reaction of ethanoyl chloride and methylamine

A

*d+ on C, d- on O and Cl of ethanoyl
*Arrow from lone pair of N (CH3NH2) to d+ C
*This produces intermediate whereby the C=O becomes C-O and CH3NH2 joins C, there is now N+ and O-
*Arrow from lone pair of O- to C-O, arrow from C-Cl to Cl and arrow from N+-H to N+.

48
Q

If the nucleophile is an alcohol, what are the products of the acylation of acyl chlorides or acid anhydrides ?

A

An ester

49
Q

Write an equation for the reaction of ethanoyl chloride and ethanol

A

CH3COCl + CH3CH2OH -> CH3COOCH2 + HCl

50
Q

Draw / describe the mechanism for the reaction of ethanoyl chloride and ethanol

A

*d+ on C, d- on O and Cl of ethanoyl chloride
*Arrow from lone pair of O (ethanol) to d+ C
*This produces intermediate whereby the C=O becomes C-O and ethanol joins C via the OH group, there is now O+ and O-
*Arrow from lone pair of O- to C-O, arrow from C-Cl to Cl and arrow from O+-H to O+.

51
Q

If the nucleophile is water, what are the products of the acylation of acyl chlorides or acid anhydrides ?

A

Carboxylic acids (hydrolyses ester linkage)

52
Q

What is the name of the reaction of the acylation of acyl chlorides/acid anhydrides with water as a nucleophile?

A

It is a hydrolysis reaction

53
Q

Write an equation for the reaction of ethanoyl chloride and water

A

CH3COCl + H2O -> CH3COOH + HCl

54
Q

Draw / describe the mechanism for the reaction of ethanoyl chloride and water

A

*d+ on C, d- on O and Cl of ethanoyl chloride
*Arrow from lone pair of O (H2O) to d+ C
*This produces intermediate whereby the C=O becomes C-O and water joins C via the O , there is now O+ and O-
*Arrow from lone pair of O- to C-O, arrow from C-Cl to Cl and arrow from O+-H to O+.

55
Q

What is a commercially important acylation reaction ?

A

The manufacture of aspirin

56
Q

What are the advantages if using ethanoic anhydride as a acylating agent over ethanoyl chloride ?

A

*It is cheaper, less corrosive and does not react readily with water
*It is safer as ethanoic acid is produced rather than HCl which is corrosive.

57
Q

What would you observe in a melting point determination if the sample was not pure ?

A

*The sample would melt over a large temperature range (more than 3 C)
*Samples melting point may be below the theory value due to impurities disrupting structure.

58
Q

Why might the melting point of a substance appear different from its true value ?

A

The temperature of the material in the apparatus may be different to the temperature reading displayed - apparatus error

59
Q

When removing flue gasses, what are the issues ?

A

Disposal of large amounts of CaSO3, and CO is produced

60
Q

What conditions are needed to form methyl esters from an acid anhydride or acyl chloride

A

React with methanol and heat gently under reflux

61
Q

When purifying via recrystallisation, why is the minimum volume of hot solvent required used ?

A

So that a saturated solution is created, this means that as many crystals will fall out of the solution as possible when it is cooled

62
Q

Why is the solution filtered hot when purifying by recrystallisation ?

A

To remove insoluble impurities and ensure that crystals do not form in the filter paper

63
Q

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

A

To ensure that as many crystals as possible fall out of solution - yield is higher

64
Q

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

A

To remove soluble impurities

65
Q

How would you separate the crystals from the reaction mixture when purifying by recrystallisation ?

A

Filter under reduced pressure using a Buchner funnel

66
Q

Why may the %yield of purifying by recrystallisation be below 100% ?

A

*Product is lost during filtration, drying and weighing - not all product is transferred from one piece of equipment to another
*Product is left dissolved in the solution - some does not crystalise
*Some is left on filter paper.

aqa a level chemistry (26 decks)

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