(8)Carboxylic Acids

Question 1

general formula for carboxylic acids

Answer 1

CₙH₂ₙO₂

    .O
	 ||
	 R--C--OH

Question 2

what are carboxylic acids called with C=C bonds

Answer 2

alkenoic acid

Question 3

physical properties

C₄ to C₈ smells

Answer 3

very strong and unpleasant odours

Question 4

physical proporties

C to C₃ smells

Answer 4

strong sharp vinegary smells

Question 5

butanoic smell examples

Answer 5

human sweat, human vomit

Question 6

physical properties

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

Answer 6

liquid

Question 7

bpt

why do carboxylic acids have a higher boiling point than alcohols

Answer 7

enhanced degree of hydrogen bonds

Question 8

bpt

why are short-chain carboxylic acids miscible in water

Answer 8

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

Question 9

preparation

how to prepare carboxylic acid from alcohol

Answer 9

prolonged reflux and distillation

Question 10

preparation

what oxidising agent is used to oxidise alcohol to cabroxylic acid

Answer 10

acidified potassium dichromate (VI) solution

Question 11

preparation

colour change in oxidisation

Answer 11

orange -> green

Question 12

preparation

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

Answer 12

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

Question 13

hydrolysis

why is pure water never used for hydrolysis of esters

Answer 13

it is too slow

Question 14

hydrolysis

what is used instead of water for hydrolysis of esters

Answer 14

dilute acid; ester is heated under reflux with dilute acid

Question 15

what is an ester

Answer 15

O
||
. .R–C–O–R’

Question 16

hydrolysis

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

Answer 16

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

Question 17

hydrolysis

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

Answer 17

• reactions are one way
• easier to seperate

Question 18

hydrolysis using dilute acid

ester + water*

*dilute acid provides water

Answer 18

⇌ carboxylic acid + alcohol

*dilute acid provides water

Question 19

hydrolysis using dilute alkali

ester + alkali (eg. NaOH)

Answer 19

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

Question 20

hydrolysis

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

Answer 20

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

Question 21

hydrolysis

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

Answer 21

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

Question 22

hydrolysis

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

Answer 22

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

Bronsted-Lowry theory

Question 23

hydrolysis

what is a nitrile

Answer 23

-C≡N

Question 24

hydrolysis

describe steps in hydrolysing of nitriles to carboxylic acids

Answer 24

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

Question 25

# hydrolysis of nitriles w/ water nitrile + water

Answer 25

amide + ammonium salt

Question 26

# hydrolysis using acid nitrile + water + acid

Answer 26

carboxylic acid + ammonium salt

Question 27

# hydrolysis nitrile + water + alkali

Answer 27

salt of carboxylic acid + ammonia gas* ## Footnote *formed from ammonium ions and hydroxide ions

Question 28

# -COOH as weak acids why are carboxylics weak acids

Answer 28

they are only partially ionised in aq solution | CH₃COOH (aq) ⇌ CH₃COO⁻ (aq) + H⁺ (aq)

Question 29

# -COOH as weak acids COOH with metals

Answer 29

metal + acid -> salt + hydrogen (MASH) | * tend to be slower than other acids

Question 30

# -COOH as weak acids (with metals) eg: magnesium with carboxylic acid

Answer 30

Mg + 2CH₃COOH -> (CH₃COO₂)Mg* + H₂ ## Footnote *magnesium ethanoate: colourless solution

Question 31

# -COOH as weak acids COOH with carbonates

Answer 31

carbonate + acid -> salt + water + carbon dioxide

Question 32

# -COOH as weak acids (with carbonates) eg. sodium carbonate with carboxylic acid

Answer 32

Na₂CO₃ + 2CH₃COOH -> 2CH₃COONa* + H₂O + CO₂ | * immediate fizzing of reactants ## Footnote *sodium ethanoate: colourlless solution

Question 33

# -COOH as weak acids COOH with bases

Answer 33

alkali/base +acid -> salt + water

Question 34

# -COOH as weak acids (with bases) eg. sodium hydroxide with carboxylic acid

Answer 34

NaOH + CH₃COOH -> CH₃COONa* + H₂O | * temperature will increase ## Footnote *sodium ethanoate: colourless solution

Question 35

# -COOH as weak acids -COOH with ammonia

Answer 35

ammonia + acid -> ammonium salt

Question 36

# -COOH as weak acids (with ammonia) eg. ammonia and carboxylic acid

Answer 36

NH₃ + CH₃COOH -> CH₃COONH₄* | * heat released ## Footnote *ammonium ethanoate: colourless solution

Question 37

# -COOH as weak acids (with ammonia) describe the reaction between ammonia and carboxylic acid

Answer 37

* 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⁺)

Question 38

# -COOH as weak acids describe practical for carboxylic acid with sodium carbonate, sodium hydroxide and ammonia.

Answer 38

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

Question 39

# -COOH reactions -COOH with alcohols

Answer 39

carboxylic acid + alcohol -> ester + water

Question 40

# COOH reactions describe what happens when carboxylic acids react with alcohols

Answer 40

* esters are produced * catalyst usually conc. sulfuric acid * slow and reversible

Question 41

# COOH reactions describe the reaction between carboxylic acids and alcohols

Answer 41

* 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

Question 42

# -COOH reactions (carboxylic acid with alcohol) eg. propanoic acid + ethanol

Answer 42

ethylpropanoate + water

Question 43

# -COOH reactions carboxylic acid with phosphorus(V) chloride

Answer 43

carboxylic acid + PCl₅ -> acyl chloride + POCl₃* + hydrogen chloride ## Footnote *phosphorus (V) trichloride oxide

Question 44

# -COOH reactions (PCl₅) describe what happens during the reaction of PCl₅ and carboxylic acid

Answer 44

* misty acidic fumes of hydrogen chloride * vigorous * heat prodcued

Question 45

# -COOH reactions (PCl₅) how to separate acyl chloride

Answer 45

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

Question 46

# -COOH reactions carboxylic acid with lithium aluminum hydride (LiAlH₄)

Answer 46

carboxylic acid + LiAlH₄ -> 1° alcohol + water

Question 47

# -COOH reactions (LiAlH₄) describe what happens during the reaction of carboxylic acid and LiAlH₄

Answer 47

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

Question 48

# -COOH reactions name dibasic and tribasic weak acids used in excess of reagents

Answer 48

* ethanedioic acid (oxalic acid) * 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid)

Question 49

# -COOH reactions what does excess reagent mean with carboxylic acids

Answer 49

all COOH groups react

Question 50

# -COOH reactions describe reaction between magnesium carbonate and oxalic acid

Answer 50

two COOH groups + MgCO₃ -> two COO in brackets beside Mg* + CO₂ + H₂O ## Footnote *magnesium ethanedioate: two COO⁻ cancels charge of Mg²⁺