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Chemistry > (8)Carboxylic Acids > Flashcards

(8)Carboxylic Acids Flashcards

1
Q

general formula for carboxylic acids

A

CₙH₂ₙO₂

    .O
	 ||
	 R--C--OH
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2
Q

what are carboxylic acids called with C=C bonds

A

alkenoic acid

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3
Q

physical properties

C₄ to C₈ smells

A

very strong and unpleasant odours

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4
Q

physical proporties

C to C₃ smells

A

strong sharp vinegary smells

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5
Q

butanoic smell examples

A

human sweat, human vomit

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6
Q

physical properties

what state are the lower members of carboxylic acids at in room temp

A

liquid

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7
Q

bpt

why do carboxylic acids have a higher boiling point than alcohols

A

enhanced degree of hydrogen bonds

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8
Q

bpt

why are short-chain carboxylic acids miscible in water

A

polar -OH group allows short chain to form H-bonds with water molecules

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9
Q

preparation

how to prepare carboxylic acid from alcohol

A

prolonged reflux and distillation

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10
Q

preparation

what oxidising agent is used to oxidise alcohol to cabroxylic acid

A

acidified potassium dichromate (VI) solution

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11
Q

preparation

colour change in oxidisation

A

orange -> green

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12
Q

preparation

what factors favour the formation of carboxylic acid and not aldehyde when oxidising alcohol

A
  • carboxylic acid: excess oxidisng agent, reaction is heated under reflux for prolonged time
  • aldehyde: mixture is distilled to remove immediately after formation
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13
Q

hydrolysis

why is pure water never used for hydrolysis of esters

A

it is too slow

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14
Q

hydrolysis

what is used instead of water for hydrolysis of esters

A

dilute acid; ester is heated under reflux with dilute acid

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15
Q

what is an ester

A

O
||
. .R–C–O–R’

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16
Q

hydrolysis

why does increasing the amount of water in reaction mixture favour the hydrolysis of ester

A

if amount of water is increased, equilibrium will shift to right to decrease amount
∴ favours forward reaction (hydrolysising the ester)

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17
Q

hydrolysis

what are the advantages of using dilute alkali and not diltue acid for hydrolysing esters

A
  • reactions are one way
  • easier to seperate
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18
Q

hydrolysis using dilute acid

ester + water*

*dilute acid provides water

A

⇌ carboxylic acid + alcohol

*dilute acid provides water

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19
Q

hydrolysis using dilute alkali

ester + alkali (eg. NaOH)

A

salt of carboxylic acid (Na attached and not H) + alcohol

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20
Q

hydrolysis

why, in the hydrolysis of esters using dilute alkali, is the salt of the carboxylic acid forming okay

A

as they are easy separated:
* no ester left
* alcohol can be distilled off

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21
Q

hydrolysis

how would you form straight carboxylic acid from hydrolysis with an acid

A

use excess of a strong acid to salt formed; reaction is flooded with H+ ions and are picked up by COO- ions to make -COOH

22
Q

hydrolysis

why does the addition of strong acid favour formation of carboxylic acid from corresponding salt

A
  • acid will readily donate H+
  • CH₃COO- is conjugate base of weak acid ∴ will accepy H+ to form carboxylic acid

Bronsted-Lowry theory

23
Q

hydrolysis

what is a nitrile

A

-C≡N

24
Q

hydrolysis

describe steps in hydrolysing of nitriles to carboxylic acids

A
  1. formation of amide (CONH₂)
  2. formation of ammonium salt of carboxylic acid (-COOH and NH₃)
25
Q

hydrolysis of nitriles w/ water

nitrile + water

A

amide + ammonium salt

26
Q

hydrolysis using acid

nitrile + water + acid

A

carboxylic acid + ammonium salt

27
Q

hydrolysis

nitrile + water + alkali

A

salt of carboxylic acid + ammonia gas*

*formed from ammonium ions and hydroxide ions

28
Q

-COOH as weak acids

why are carboxylics weak acids

A

they are only partially ionised in aq solution

CH₃COOH (aq) ⇌ CH₃COO⁻ (aq) + H⁺ (aq)

29
Q

-COOH as weak acids

COOH with metals

A

metal + acid -> salt + hydrogen (MASH)

* tend to be slower than other acids

30
Q

-COOH as weak acids (with metals)

eg: magnesium with carboxylic acid

A

Mg + 2CH₃COOH -> (CH₃COO₂)Mg* + H₂

*magnesium ethanoate: colourless solution

31
Q

-COOH as weak acids

COOH with carbonates

A

carbonate + acid -> salt + water + carbon dioxide

32
Q

-COOH as weak acids (with carbonates)

eg. sodium carbonate with carboxylic acid

A

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

* immediate fizzing of reactants

*sodium ethanoate: colourlless solution

33
Q

-COOH as weak acids

COOH with bases

A

alkali/base +acid -> salt + water

34
Q

-COOH as weak acids (with bases)

eg. sodium hydroxide with carboxylic acid

A

NaOH + CH₃COOH -> CH₃COONa* + H₂O

* temperature will increase

*sodium ethanoate: colourless solution

35
Q

-COOH as weak acids

-COOH with ammonia

A

ammonia + acid -> ammonium salt

36
Q

-COOH as weak acids (with ammonia)

eg. ammonia and carboxylic acid

A

NH₃ + CH₃COOH -> CH₃COONH₄*

* heat released

*ammonium ethanoate: colourless solution

37
Q

-COOH as weak acids (with ammonia)

describe the reaction between ammonia and carboxylic acid

A
  • carboxylic acid, hydrogen ion transfers to lone pair on :N in ammonia
  • carboxylic acid then has a lone pair and -ve charge on the single bond C-O:
  • ammonium is formed with a +ve charge (NH₄⁺)
38
Q

-COOH as weak acids

describe practical for carboxylic acid with sodium carbonate, sodium hydroxide and ammonia.

A
  • place 1cm³ carboxylic acid in boiling tube
  • record pH using pH paper
  • add spatula measure of Na2CO₃/NaOH/NH₃
  • record pH
39
Q

-COOH reactions

-COOH with alcohols

A

carboxylic acid + alcohol -> ester + water

40
Q

COOH reactions

describe what happens when carboxylic acids react with alcohols

A
  • esters are produced
  • catalyst usually conc. sulfuric acid
  • slow and reversible
41
Q

COOH reactions

describe the reaction between carboxylic acids and alcohols

A
  • carboxylic acid H is removed
  • alcohol OH is removed
  • ester formed, water formed from H and OH
  • ester: alcohol part becomes -yl group and carboxylic acid becoming the -oate

*condensation reaction

42
Q

-COOH reactions (carboxylic acid with alcohol)

eg. propanoic acid + ethanol

A

ethylpropanoate + water

43
Q

-COOH reactions

carboxylic acid with phosphorus(V) chloride

A

carboxylic acid + PCl₅ -> acyl chloride + POCl₃* + hydrogen chloride

*phosphorus (V) trichloride oxide

44
Q

-COOH reactions (PCl₅)

describe what happens during the reaction of PCl₅ and carboxylic acid

A
  • misty acidic fumes of hydrogen chloride
  • vigorous
  • heat prodcued
45
Q

-COOH reactions (PCl₅)

how to separate acyl chloride

A

fractional distillation; test with glass rod dipped in conc. NH₃⁻ -> white fumes

46
Q

-COOH reactions

carboxylic acid with lithium aluminum hydride (LiAlH₄)

A

carboxylic acid + LiAlH₄ -> 1° alcohol + water

47
Q

-COOH reactions (LiAlH₄)

describe what happens during the reaction of carboxylic acid and LiAlH₄

A
  • carboxylic acid is reduced to an aldehyde
  • aldehyde is further reduced to primary alcohol
  • reduction carried under reflux with lithal, LiAlH₄ in dry ether
48
Q

-COOH reactions

name dibasic and tribasic weak acids used in excess of reagents

A
  • ethanedioic acid (oxalic acid)
  • 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid)
49
Q

-COOH reactions

what does excess reagent mean with carboxylic acids

A

all COOH groups react

50
Q

-COOH reactions

describe reaction between magnesium carbonate and oxalic acid

A

two COOH groups + MgCO₃ -> two COO in brackets beside Mg* + CO₂ + H₂O

*magnesium ethanedioate: two COO⁻ cancels charge of Mg²⁺

Chemistry (8 decks)

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