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Aqa a level chemistry > Organic Chemistry - carboxylic acids > Flashcards

Organic Chemistry - carboxylic acids Flashcards

1
Q

dissociation of carboxylic acids

A

-carboxylic acids = weak acids = partially dissociate to form H+ ions in solution

-smaller carboxylic acids dissolve in water because they can form hydrogen bonds with other molecules of water

COOH –> COO- + H+

-carboxylic acid salts are stabilised by delocalisation

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2
Q

ethanol structural formula

A

CH3-CH2-OH

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3
Q

test for carboxylic acids

A

The effervescence caused by production of CO2
with carboxylic acids with solid Na2CO3 or
aqueous NaHCO3 can be used as a functional
group test for carboxylic acids

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4
Q

uses of esters

A

Esters are sweet smelling
compounds that can be used in
perfumes and flavourings.
For use in perfumes they need to be non toxic, soluble in solvent such as
ethanol, volatile (turns into gas easily), and not react with water.

Esters can be used as solvents
for polar organic substances.
Ethyl ethanoate is used as a
solvent in glues and printing inks.

Although polar, they do not form hydrogen bonds (reason: there is no
hydrogen bonded to a highly electronegative atom).
They have a lower b.p. than the hydrogen-bonded carboxylic acids

They are also almost insoluble in water.
Esters can be used as
plasticisers for polymers.
Often pure polymers have limited flexibility because the polymer chains
cannot move over each other.
Incorporating some plasticiser into the polymer allows the chains to move
more easily and the polymer can become more flexible

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5
Q

hydrolysis of esters

A

i) with acid
reagents: dilute acid (HCl)
conditions: heat under reflux

ii) with sodium hydroxide
reagents: dilute sodium hydroxide
conditions: heat under reflux

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6
Q

carboxylic acids

A

-carboxylic acids = weak acids = partially dissociate to form H+ ions in solution

-smaller carboxylic acids dissolve in water because they can form hydrogen bonds with other molecules of water

-carboxylic acid salts are stabilised by delocalisation

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7
Q

acid + base

A

-acid + base –> salt + water

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8
Q

acid + metal carbonate

A

-acid + metal carbonate –> salt + CO2 + H2O

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9
Q

acid + metal

A

-acid + metal –> salt + hydrogen

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10
Q

metal oxide

metal hydroxide

A

-metal oxide –> metal salt + water

-metal hydroxide- -> metal salt and water

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11
Q

HCL + metal carbonate

A

HCl + Na2CO3 –> NaCl + CO2 + H2O

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12
Q

ethanoic acid + sodium carbonate

A

CH3COOH + Na2CO3 –> CH3COONa + CO2 + H2O

Ethanoic acid + sodium carbonate –> sodium ethanoate + carbon dioxide + water

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13
Q

structural formula of a carboxylic acid

A

Structural formula of a carboxylic acid

e.g propanoic acid = CH3-CH2-COOH

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14
Q

formation

A

Propanoic acid + sdoium hydroxde –> sodium propanoate + H2O

Carboxylic acids can react in the presence of an acid catalyst to make esters

Carboxylic acids = weak acids

HCl dissociates to H+ and Cl-

Carboxylic acids like ethanoic acid dissociate into ethanoate ions and hydrogen ions

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15
Q

observation when adding sodium hydrocarbonate to ethanoic acid

A

Observation when adding sodium hydrocarbonate to ethanoic acid:

-effervescence when CO2 gas is evolved

-colourless solution of sodium ethanoate

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16
Q

functional group of carboxylic acids

A

-carbon is open to attack from nucleophilles

-oxygen from C=O can be attacked by postively paired species

-H+ may be lost as it is behaving like an acid

Carboxylic acid + metal –> salt + hydrogen

Acid plays the role of a catalyst in the hydrolysis of esters

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17
Q

acyl chlorides and anhydrides

A

-general formula = RCOCl

-all carboxylic acids contain a carbonyl group

-SOCl2 = oxidation state of sulfur = +4

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18
Q

room temp

A

Oil = liquid at room temperature

Solid at room temperature = fat

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19
Q

acid anhydride

A

-formation of this is a reversible reaction

-2 molecules of ethanoic acid can be dehydrated to ethanoic anhydride

-general formula = RCOOCOR

-two acyl (carbonyl) groups bonded to the same oxygen atom.

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20
Q

nucelophillic addition-elimination

A

When 2 pi bonds break and a sigma bond forms this is called an eliminaton reaction

This reacton shown above is a nucelophilic addition-elimination

Butanoyl chloride + propanol –> propyl butanoate + HCl (this reaction must take place in ahydrous conditions)

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21
Q

forming esters equation

A

Carboxylic acid + alcohol ⇌ ester + water

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22
Q

conditions for esterification

A

-Esterfication includes a concentrated acid catalyst e.g sulfuric acid

-heat

-little water

O-C=O = ester bond

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23
Q

propanoic acid + methanol

A

Propanoic acid + methanol ⇌ methylpropanoate + H2O

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24
Q

methanoic acid + propan-2-ol

A

Methanoic acid + propan-2-ol ⇌ methylethyl ethanoate + waer

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25
Q

acid hydrolysis of esters

A

-ester + water ⇌ carboxylic acid + alcohol

-reversible reaction

Conditions –> acid catalyst e.g sulfuric acid, heat, excess water, 60 degrees

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26
Q

base hydrolysis of esters

A

-non-reversible reaction

-ester + KOH -> R=O-C-O-K + alcohol

-e.g ethyl acetate + sodium hydroxide –> sodium acetate + ethanol

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27
Q

uses of esters

A

-Vegetable oils and animal fats are esters of propane-1,2,3-triol (glycerol).

-Vegetable oils and animal fats can be hydrolysed in alkaline conditions to give soap (salts of long-chain carboxylic acids) and glycerol.

-Biodiesel is a mixture of methyl esters of long-chain carboxylic acids.

-Biodiesel is produced by reacting vegetable oils with methanol in the presence of a catalyst.

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28
Q

types of fats

A

-saturated fat = only single bonds = high melting point = solid at room temp

-unsaturated fat = double bonds = liquid at room temp due bends/kinks in hydrocarbon chain

-trans fat = hydrogen atoms on opposite sides of double carbon bond = no bending = formed via partial hydrogenation of unsaturated fats

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29
Q

fat molecule

A

Fat molecule = 1 glycerol molecule and 3 fatty acids

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30
Q

soaps

A

Soaps = sodium salts formed when triglycerides are hydrolysed using NaOH and heat

-salts dissociates into Na+ and RCOO- in solution. RCOO- molecules have one end which mixes with water and one end that mixes with organic grease. Allows grease + water to mix

Fatty acid + NaOH –> salt + glycerol = base hydrolysis of fats

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31
Q

biodiesel

A

-renewable as it is made from vegetable oils

-triglycerides are reacted with methanol with NaOH catalyst to form glycerol and methyl esters which can be used as fuel

-this s known as a transesterifcation reaction where the alcohols group swap

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32
Q

delocalisation

A

The delocalised ion has equal C-O bond lengths. If delocalisation did not occur, the C=O bond would be shorter than the C-O bond. The pi charge cloud has delocalised and spread out. The delocalisation makes the ion more stable and therefore more likely to form.

-Increasing chain length pushes electron density on to the COO- ion, making it more negative and less stable. This make the acid less strong. E.g propanoic acid is less acidic than ethanoic acid

33
Q

acid anhydride

A

R(CO)2O

34
Q

acyl chloride

A

RCOCl

35
Q

propanoic anhydride + ethylamine

A

ehtyl propanamide + CH3CH2C=OO- + H2N-CH3-CH2

36
Q

acyl chloride reactivity

A

Acyl chlorides react more violently with water than acid anhydride

Carboxylic acids need a catalyst to react with alcohols

Order of reactivity:

Acyl chlorides –> acid anhydride –> carboyxlic acids (most to least reactive)

Acyl chlorides = most open to nucelophillic attack

37
Q

Oil + methanol

A

Oil + methanol –> biodiesel + glycerol

Methanol = CH3OH

Biodiesel = R-O=C-O-CH3

Glycerol = 3x CH2OH

38
Q

what is acylation

A

-the process where an acyl group is added to another molecule

39
Q

acyl chloride + alcohol

A

Acyl chloride + alcohol (R-O-H) –> R-O=C-O-R (ester) + HCl

40
Q

propanoyl chloride reactions

A

Propanoyl chloride + ethanol –> ethyl propanoate + HCl

Propanyol chloride + water –> propanoic acid + HCl

41
Q

ethanoyl chloride + ammonia

A

ethanoylchloride + ammonia (NH3) –> ethyl amine + Cl- + NH4+

42
Q

reaction of CH3CH2COCl with ammonia

A

nucelophilic addition elimination

43
Q

CH3CH2CH2Cl with excess ammonia

A

nucelophilic subsiution

44
Q

Ethanoic anhydride + methylamine –>

A

methylammonium ethanoate + methylammonia

45
Q

water + propanoyl chloride

A

propanoic acid + HCl

46
Q

equations

A

2Ammonia + ethanoyl chloride –> ethanamide + [NH4+Cl-]

Propan-2-ol + ethanoyl chloride –> propan-2-oic acid + HCl

47
Q

properties of acyl chloride

A

-reactive

-corrosive

-expensive

-harmful products

48
Q

properties of acid anhydrides

A

cheaper

-less corrosive

-safer

-less reactive

49
Q

why are anhydrides used as acyling agents

A

Despite acyl chloride having a higher atom economy, acid anhydrides are generally used as acyling agents because its cheaper and less corrosive, doesn’t react with water as readily and safer as biproduct is ethanoic acid not HCl

50
Q

NH3 + H2O

A

NH3 (aq) +H2O (l) ⇌NH4+(aq)+OH-(aq)

51
Q

sodium benzonate

A

Sodium benzoate is soluble in water because it is ionic. Benzoic acid, however, is insoluble. This is because even though the polar COOH group can form hydrogen bonds, the benzene ring is non-polar. In organic compounds there are often polar parts and non-polar parts. The solubility in water of a compound will controlled by whether the polar or non polar part is of greater importance.

52
Q

hydrolysis of ethylbenzaonate

A

Hydrolysis of ethylbenzanoate:

ethyl benzoate + NaOH –> sodium benzoate + ethanol

53
Q

fats and soaps

A

-Fats and oils are esters of glycerol and long chain carboxylic acids (fatty acids)

-Vegetable oils and animal fats can be hydrolysed to give soap, glycerol and long chain carboxylic (fatty) acids

-Glycerol (propane-1,2,3-triol) forms hydrogen bonds very easily and is readily soluble in water. It is used in cosmetics, food and in glues

54
Q

acyl chlorides more reactive than carboxylic acids

A

Acyl chlorides are much more reactive than carboxylic acids

Acid anhydrides have a similar reactivity to acyl chlorides and therefore bring about the same changes in functional groups. The main difference is the by- products. Acyl chlorides mostly give off HCl. Acid anhydrides give off RCOOH

55
Q

acyl chloride reactions

A

Acyl chloride + water –> carboxylic acid + HCl

Observation = white steamy fumes of HCl are given off

Acyl chloride + alcohol –> ester + HCl

Acyl chloride + 2NH3 –> primary amide + NH4Cl

56
Q

acid anhydrides

A

Acid anhydride + water –> 2 carboxylic acid

Acid anhydride + alcohol –> ester + alcohol

Acid anhydride + 2NH3 –> primary amide + RCO2- + NH4+

57
Q

benzene

A

In benzene, 6p orbitals overlap to form a pisystem containing delocalisedelectrons.

58
Q

ethanoic acid + sodium carbonate

A

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

59
Q

acid anhydride + alcohol

A

ester + carboxylic acids

60
Q

properties of esters

A

polar
low boiling points

61
Q

unsaturated fats like vegetable oil

A

less van der waals = lower boiling points

62
Q

fat ester =

A

saturated

fat + 3NaOH –> glycerol + 3soap

soap = RCOO-Na+

63
Q

oil + methanol

A

glycerol + methyl ester

3H3C-O-C=O-R

64
Q

acyl chloride + NH3

A

amide + HCl

e.g ethananmide

65
Q

ethanoic anhydride + water

A

ethanoic acid x2

66
Q

vegetable oil =

A

CH2 - O - C=O - CxHx
[
[
CH - O - C=O - CxHx
[
[
CH2-O-C=O-CxHx

67
Q

give the equation for the reaction of CH3CH2COCl and AlCl3

A

CH3CH2CO+ + AlCl4-

68
Q

give the reagent and conditions for ester to alcohol

A

NaOH
aqueous/warm
fractional distillation to separate alcohol

69
Q

KCN reagents + conditions

A

alcoholic
heat
H2

70
Q

name the type of compound formed by the formula RCOOK

A

carboxylate salt

use = salt

71
Q

suggest why aqueous ethanol is a suitable solvent when heating oil with KOH and precatuions

A

reason = to dissolve both the oil and KOH

precautions = use water bath for heating mixture = prevents risk of fire since ethanol is flammable

72
Q

reagents for elimination reaction (dehydration)

A

concentrated H2SO4

73
Q

Alkene + Br2 = dibromoalkane

dibromoalkane + NAOH –>

A

diol e.g 1,2dipropanol + 2NABr

74
Q

why chemists aim to use fewer steps

A

less energy

75
Q

high percentage atom economy =

A

high yield

76
Q

hazard of phosphoric acid

A

corrosive

77
Q

2 ways in which the melting point of crude asprin would differ to pure asprin

A

lower melting point

range of values

78
Q

purpose of adding small amount of cold ethanol

A

remove any soluble impurities

79
Q

which reaction involves addition-elimination

A

CH3COCl + C6H5OH –> CH3COOC6H5 + HCl

Aqa a level chemistry (26 decks)

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