A level- Chemistry > Acids, Esters and Polyesters > Flashcards

Acids, Esters and Polyesters Flashcards

(43 cards)

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1
Q

What is the carboxyl functional group

A

A group that contains both a carbonyl group and a hydroxyl group.

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2
Q

What type of intermolecular forces are present in carboxylic acids

A
  1. London forces
  2. Permanent dipoles
  3. Hydrogen bonds
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3
Q

Why can carboxylic acids form hydrogen bonds

A
  1. The C=O and O-H bonds are polar allowing carboxylic acids to form hydrogen bonds
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4
Q

Describe the solubility of carboxylic acids

A
  1. Carboxylic acids with up to 4 carbons atoms are soluble in water
  2. They can form hydrogen bonds with water
  3. As the number of carbon atoms increases, the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule.
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5
Q

Describe properties of dicarboxylic acids

A
  1. Have two polar carboxyl groups to form hydrogen bonds
  2. They are solids at room temperature
  3. Dissolve readily in water
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6
Q

Name the type of acid and show the equation when carboxylic acids are dissolved in water

A
  1. Weak acid

2. HCOOH ↔ H+(aq) + HCOO- (aq)

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7
Q

Name the salts formed from carboxylic acids

A

Carboxylates

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8
Q

Name two types of acid reactions carboxylic acids take part in

A
  1. Redox reactions with metals

2. Neutralisation reactions with bases

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9
Q

Describe the redox reaction of a carboxylic acid reacting with a metal, and show the equation for the reaction of propanoic acid with Magnesium

A
  1. Aqueous solutions of carboxylic acids react with metals in a redox reaction
  2. They form hydrogen gas and a carboxylate salt
  3. The metal disappears/dissolves and effervescence can be seen
  4. 2CH3CH2COOH (aq) + Mg (s) → (CH3CH2COO-)2Mg2+(aq) + H2 (g)
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10
Q

Describe the reaction between a carboxylic acid and a metal oxide, and give an example with ethanoic acid and calcium oxide

A
  1. Form salt and water

2. 2CH3COOH (aq) + CaO (s) → (CH3COO-)2 Ca2+ (aq) + H2O (l)

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11
Q

Describe the reaction between a carboxylic acid and an alkali, and give an example with ethanoic acid and sodium hydroxide, write ionic equation as well

A
  1. Form salt and water
  2. May not see anything as two solutions mix to form an aqueous solution of the salt
  3. CH3COOH (aq) + NaOH (aq) → CH3COO-Na+ (aq) + H2O (l)
  4. H+ (aq) + OH-(aq) → H2O (l)
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12
Q

Describe the reaction between a carboxylic acid and carbonates, and give an example with ethanoic acid and sodium carbonate

A
  1. Carbon dioxide produced
  2. If carboxylic acid is in excess a solid carbonate would disappear
  3. 2CH3COOH (aq) + Na2CO3 (aq) → 2CH3COO-Na+ (aq) + H2O (l) + CO2 (g)
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13
Q

Describe the test for a carboxyl group

A
  1. Neutralisation reaction of carboxylic acids with carbonates e.g sodium carbonate
  2. Carboxylic acids are the only common organic compounds sufficiently acidic to react with carbonates,
  3. Especially useful for distinguishing between phenols and carboxylic acids, as phenols aren’t acidic enough
  4. Effervescence is produced
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14
Q

Name 3 derivatives of carboxylic acids

A
  1. Acyl chloride
  2. Acid anhydride
  3. Ester
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15
Q

What is a derivative of a carboxylic acid

A
  1. A compound that can be hydrolysed to form the parent carboxylic acid.
  2. They all contain an acyl group- Carbon bonded to R group, something else and a double bond to an oxygen
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16
Q

How do you name an acyl chloride and what do they look like

A
  1. It is named after the parent carboxylic acid from which it is derived
  2. Remove the oic acid suffix and replace with -oyl chloride
  3. Carbon attached to R group, double bonded to O and bonded to a Chlorine
  4. Number of carbon atoms relates e.g. propanoyl or butanoyl
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17
Q

How are acid anhydrides formed and show equation of the formation of ethanoic anhydride

A
  1. By the removal of water from two carboxylic acid molecules
  2. CH3COOH + CH3COOH → CH3COOCOCH3 + H2O
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18
Q

Describe how to form an ester from a carboxylic acid and an alcohol

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A
  1. Esterification

2. Alcohol is warmed with carboxylic acid with small amount of concentrated sulfuric acid catalyst

19
Q

Show the reaction between propanoic acid and ethanol

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A
  1. CH3CH2COOH + CH3CH3OH → CH3CH2COOCH2CH2 + H2O

2. Forms ethyl propanoate

20
Q

Define hydrolysis reaction

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A
  1. A reaction with water that breaks a chemical compound into two compounds, the H and the OH in the water molecule becomes incorporated into the two compounds
21
Q

Name the two ways that an ester can be hydrolysed

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A
  1. Acid hydrolysis

2. Alkali hydrolysis

22
Q

Describe how to hydrolyse an ester with acid hydrolysis

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A
  1. Heated under reflux with dilute aqueous acid
  2. The ester is broken down by water, with the acid acting as a catalyst
  3. The products are a carboxylic acid and an alcohol
23
Q

Show the equation for acid hydrolysis

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A
  1. Ester + water ↔ alcohol + carboxylic acid
  2. Dilute H2SO4 (aq) or HCl (aq) (reagents as contain H2O but aren’t written in equation)
  3. Heat under reflux
24
Q

Why do you use a dilute acid in the hydrolysis of an ester

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A
  1. Acid hydrolysis is the reverse equation of esterification
  2. A dilute aqueous acid contains H2O so moves the equilibrium to the right.
  3. CH3COOCH3 + H2O ↔ CH3OH + CH3COOH
25
Why is it impossible to achieve 100% yield from acid hydrolysis of esters
It is a reversible reaction, so only an equilibrium yield is reached
26
Describe how to hydrolyse an ester with alkaline hydrolysis
1. Heat under reflux with aqueous hydroxide ions 2. Irreversible reaction 3. Produces a carboxylate ion and an alcohol
27
Show the equation for alkaline hydrolysis and give example with methyl ethanoate and sodium hydroxide
1. Ester + OH- → Carboxylate ion + Alcohol | 2. CH3COOCH3 + NaOH → CH3COO-Na+ + CH3OH
28
How can a carboxylic acid be recovered from a carboxylate salt
1. Weak acids do not fully dissociate in aqueous solution to release H+ ions, but exist in one equilibrium 2. RCOOH ↔ ROO- + H+ 3. The carboxylate salt in aqueous solution exists as separate RCOO- ions and positive metal ions. 4. If a strong acid such as HCl (aq) were added, the H+ ions will react with the carboxylate ions to form undissociated carboxylic acid. 5. So acidification of the salt solution will allow us to recover the carboxylic acid
29
How can acyl chlorides be prepared
1. From their parent carboxylic acid reacting with thionyl chloride SOCl2. 2. Other products SO2 and HCl are evolved as gases, leaving just the acyl chloride
30
Write equation for the reaction for the formation of propanoyl chloride
1. CH3CH2COOH + SOCl2 → CH3CH2COCl + SO2 + HCl
31
How can acyl chlorides make an ester
1. React with alcohol or phenol | 2. Form ester and HCl
32
Write equations for the reactions of ethanoyl chloride with propan-1-ol and ethanoyl chloride with phenol
1. CH3COCl + CH3CH2CH2OH → CH3COOCH2CH2CH3 +HCl | 2. CH3COCl + phenol → CH3COObenzene ring + HCl
33
Write equation and observations that would form if ethanoyl chloride reacted with water
1. Violent reaction 2. Evolution of dense steamy hydrogen chloride fumes 3. CH3COCl + H2O → CH3COOH + HCl
34
Describe the reaction between acyl chlorides and ammonia and give example with ethanoyl chloride
1. Ammonia can act as a nucleophile by donating the lone pair of electrons on the nitrogen atom to an electron-deficient species 2. Forms primary amides when reacting with acyl chlorides (Nitrogen atom attached to one carbon atom) 3. CH3COCl + 2NH3 → CH3CONH2 + NH4Cl
35
Describe the reaction between acyl chlorides and amines and give an example with ethanoyl chloride and methyl primary amine
1. Primary amine reacts with acyl chloride in the same way as ammonia to form secondary amide (Nitrogen atom attached to two carbon atoms) 2. CH3COCl + 2CH3NH2 → CH3CONHCH3 + CH3NH3+Cl-
36
What is more reactive acyl chlorides or acid anhydrides
1. Acyl chlorides are more reactive
37
Describe how to make an ester from an acid anhydride
1. React with alcohol | 2. Forms ester and carboxylic aid
38
Write equation to show the reaction between ethanoic anhydride and phenol
1. 2(CH3CO)2O + C6H5OH → CH3COOC6H5 + CH3COOH | 2. Ethanoic anhydride + phenol → phenyl ethanoate + ethanoic acid
39
State the two functional groups that must be present in monomers to form a polyester
1. Carboxylic acid | 2. Alcohol
40
What are the different combinations of monomers that could lead to the formation of a polyester
1. Dicarboxylic acid and diol | 2. Hydroxycarboxylic acid
41
What is the name of the reaction that forms polyesters
Condensation reactions
42
How do you write equations for the formation of polyesters
1. n Reactants → (product)n + (2n-1)H2O 2. In the product you should see a ester where the two reactants have joined. 3. Only one single bond O should be left dangling at the end 4. If you joined one end of the product in brackets with other end it would join to make ester.
43
Name the two ways a polyester can be hydrolysed
1. Base hydrolysis- NaOH/H2O 2. Acid hydrolysis- H+/H2O 3. Will form the two monomers that made that polyester
A level- Chemistry
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