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Chem Mock > carboxylic acid > Flashcards

carboxylic acid Flashcards

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1
Q

what does carboxylic acids contain

A

the carboxyl functional group, -COOH

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2
Q

formula for carboxylic acid

A

CnH2n+1COOH which can be shortened to just RCOOH

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3
Q

why is the intermolecular forces that carboxylic acids experience be high

A

because carboxylic acids contain two polarised groups C=O and O-H and they will have relatively high melting points and boiling points

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4
Q

what does the presence of O-H bond in carboxylic acid allow

A

exhibit hydrogen bonding
Not only does this contribute to the high melting and boiling points, it also contributes to the solubility in water

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5
Q

carboxylic acids can be formed from the oxidation of….

A

primary alcohols and aldehydes by either acidified K2Cr2O7 or acidified KMnO4 and reflux

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6
Q

what do the oxidising agents get reduced to
K2Cr2O7
KMNO4

A

In K2Cr2O7 the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions

In KMnO4 the purple manganate ions (MnO4-) are reduced to colourless Mn2+ ions

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7
Q

carboxylic acids can be prepared from the hydrolysis of …

A

hydrolysis of nitriles using either dilute acid or dilute alkali followed by acidification

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8
Q

what does the hydrolysis of nitriles by dilute acid result in

A

formation of a carboxylic acid and ammonium salt

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9
Q

what does the hydrolysis of nitriles by dilute alkali result in

A

formation of a sodium carboxylate salt and ammonia; Acidification is required to change the carboxylate ion into a carboxylic acid

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10
Q

what does partial ionisation of carboxylic acids mean

A

that carboxylic acids are weak acids

This means that the position of the equilibrium lies to the left and that the concentration of H+ is much smaller than the concentration of the carboxylic acid

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11
Q

what do carboxylic acids ionise to form

A

low concentrations of hydronium ions and alkanoate ions

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12
Q

what is a test for the presence of carboxylic acid

A

NaHCO3 / Na2CO3 - effervescence / bubbles limewater turn milky

add alcohol should turn into ester and distinctive smell

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13
Q

what do carboxylic acid undergo when reacted with LIAlH4

A

undergo reduction when they react with a reducing agent such as lithium tetrahydridoaluminate, LiAlH4

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14
Q

what is Carboxylic acid reduced to

A

primary alcohol

Addition of water at the end will destroy any excess lithium tetrahydridoaluminate

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15
Q

what does carboxylic acids form when reacted with bases such as metals alkalis and carbonates

A

metal oxides: metal salt and hydrogen gas

alkalis: alt and water are formed in a neutralisation reaction

carbonates: metal salt, water and carbon dioxide gas are produced

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16
Q

what is formed when carboxylic acid reacts with solid phosphorus(V) chloride

A

acyl chloride

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17
Q

what will propanoic acid (PCl5) react with phosphorus chloride to form

physical observations?

A

propanoyl chloride, phosphorus trichloride oxide and hydrogen chloride

CH3CH2COOH (l) + PCl5 (s) →

CH3CH2COCl (l) + POCl3 (l) + HCl (g)

steamy fumes of HCl are produced

18
Q

what is formed when carboxylic acid reacts with alcohol

A

an ester is formed

19
Q

what are esters

A

compounds with an -COOR functional group and are characterised by their sweet and fruity smells

20
Q

how are esters formed

A

condensation reaction between a carboxylic acid and alcohol with concentrated H2SO4 as catalyst
This is also called esterification

21
Q

how do you name an ester

A

The first part of the ester’s name comes from the alcohol and the second part of the name comes from the carboxylic acid

e.g. ethyl propnaoate

22
Q

what is the reverse of esterification and what is this useful for

A

hydrolysis of Esters for creating biodegradable plastics

23
Q

how can esters be hydrolysed

A

by using either dilute acid (e.g. sulfuric acid) or alkali (e.g. sodium hydroxide) and heat

24
Q

what happens when ester heated under reflux with alkali

A

irreversible reaction as the ester is fully hydrolysed and the reaction goes to completion

The carboxylic acid produced reacts with excess alkali to form a carboxylate salt and alcohol
The sodium carboxylate salt requires further acidification to turn into a carboxylic acid

25
Q

what are acyl chlorides

A

derivatives of carboxylic acids by substitution of the -OH group by a chlorine atom

26
Q

how can acyl chlorides be named

A

Acyl chlorides are named by identifying the parent hydrocarbon chain and adding the suffix -oyl chloride

They can also be named by removing the -oic acid from the carboxylic acid and adding -oyl chloride

27
Q

what are acid anhydrides

A

erivatives of carboxylic acids formed by substitution of the -OH group by an alkanoate

28
Q

how can acid anhydrides be named

A

Acid anhydrides are named by identifying the parent hydrocarbon chain and adding the suffix -oic anhydride

They can also be named by removing the -oic acid from the carboxylic acid and adding -oic anyhydride

29
Q

what are examples of nucleophilic addition elimination reactions

A

Hydrolysis

Reaction with alcohols to form esters

Reaction with ammonia and primary amines to form amides

30
Q

what does hydrolysis of acyl chlorides form

A

carboxylic acid and HCl molecule

31
Q

what is the nucleophilic addition elimination reaction of the hydrolysis of acyl chlorides

A

A water molecule adds across the C=O bond
A hydrochloric acid (HCl) molecule is eliminated

32
Q

explain the nucleophilic addition-elimination reaction for the formation of esters

A

Acyl chlorides can react with alcohols to form esters

The alcohol adds across the C=O bond
A HCl molecule is eliminated

A HCl molecule is eliminated

33
Q

what do acyl chlorides form when reacted with primary amines and concentrated ammonia

A

amides

34
Q

how can acyl chlorides form amides with primary amine or concentrated ammonia

A

The nitrogen atom in ammonia and primary amine has a lone pair of electrons which can be used to attack the carbonyl carbon atom in the acyl chlorides

The product is an amide (when reacted with ammonia) or N-substituted amide (when reacted with primary amines)

This is also an example of a nucleophilic addition-elimination reaction as
The amine or ammonia molecule adds across the C=O bond
A HCl molecule is eliminated

35
Q

how are addition polymers made

A

They are made using monomers that have C=C double bonds joined together to form polymers such as polyethene

36
Q

what are condensation polymers

A

reaction whereby a polymer is produced by repeated condensation reactions between monomers

Natural condensation polymers are all formed by elimination of water

37
Q

how is polyester formed

A

by the reaction between dicarboxylic (2 -COOH groups) acid monomers and diol monomers ( 2 -OH groups)

linking these monomers with ester bonds / links

When the polyester is formed, one of the -OH groups on the diol and the hydrogen atom of the -COOH are expelled as a water molecule (H2O)

38
Q

can you form polyesters with one monomer

A

A single monomer containing both of the key functional groups can also be used

These monomers are called hydroxycarboxylic acids
They contain an alcohol group (-OH) at one end of the molecule while the other end is capped by a carboxylic acid group (-COOH)

39
Q

three differences in the esterification reaction when acyl chloride used instead of carboxylic acid

A
  • the reaction is irreversible compared to reversible (1)
  • hydrogen chloride is the by-product rather than water (1)
  • the reaction is very fast/occurs at room temperature so
    an acid catalyst is not needed (1)
40
Q

compare contrast two methods of hydrolysis for esters

acid/alkali

A

(similarity)
* both make the (same) alcohol / pentan-1-ol
(differences)
acid hydrolysis is reversible, alkaline hydrolysis is irreversible
(1)
(1)
acid hydrolysis produces the carboxylic acid/ ethanoic acid and
(ion)
alkaline hydrolysis produces the carboxylate / ethanoate
(1)
the acid is a catalyst and the alkali is a reactant

41
Q

3 differences between esterfication reaction when you use ethanoyl chloride vs ethanoic acid

A

(with ethanoyl chloride)
the reaction is irreversible compared to reversible (1)

hydrogen chloride is the by-product rather than water (1)

the reaction is very fast/occurs at room temperature so
an acid catalyst is not needed (1)

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