2022 Paper 2 Chemistry corrections

Question 1

What are the use of waste poly(alkenes)

Answer 1

• feedstock for cracking
• incineration to release energy
  -make new materials by recycling

Question 2

What is a diol?

Answer 2

Compound contains two hydroxyl (-OH) groups

Question 3

Why would 2,2-dimethylpropane have a lower boiling point than its isomer pentane?

Answer 3

There are less London forces due to less points of contact

Question 4

What is the difference between heterolytic bond fission and homolytic bond fission?

Answer 4

Homolytic fission occurs when the covalent bond breaks evenly, and each of the bonded atoms takes one of the shared pair of electrons from the bond. Each atom now has a single unpaired electron - called a radical.

Heterolytic fission: When the covalent bond breaks unevenly, and one of the bonded atoms takes both of the electrons from the bond.The atom that takes both electrons becomes a negative ion (anion).The atom that does not take the electrons becomes a positive ion (cation).

Question 5

What is the classification of this dihalogenoalkane and why

Answer 5

Primary because both chlorine atoms are bonded to carbon atoms bonded to only one other carbon atom

Question 6

Give a reason as to why nitrogen gas and not air is used in packet of crisps

Answer 6

Prevents oxidation of crisps

• Remember that air contains roughly 20% oxygen and so it is not unusual for oxidation to be a result when chemicals are exposed to the air.

Question 7

Why does a nitrogen molecule have six shared electrons

Answer 7

Each electron pair is one bond
Nitrogen has three bonds between its atoms (triple bond)

Question 8

Explain why ammonia molecule and the ammonium ion have different shapes and bond angles

Answer 8

Ammonia has a lone pair of electrons which repels more than bonded pairs of electrons
- Ammonia has three bond pairs of electrons and one lone pair
- Ammonia is trigonal pyramidal
Ammonium ion is tetrahedral
- Ammonia bond angle is 107
- Ammonium ion is 109.5

Question 9

Butylamine, C4H9NH2 , reacts with ethanoyl chloride.
2C4H9NH2 + CH3COCl → C4H9NHCOCH3 + C4H9NH3+Cl–
Explain how this equation illustrates that butylamine acts as a nucleophile and as a base.

Answer 9

Amine group attacks as a nucleophile by attacking the C+ of the acyl chloride to produce hydrogen chloride.
It is also a base because the amine group reacts with acid/protons to produce C4H9NH3+Cl-.

Question 10

What is ethanoyl chloride

Answer 10

An acyl chloride

Question 11

What is butylamine

Answer 11

A typical amine

Question 12

Ethanoyl chloride reacts with cold conc. solution of ethy

Answer 12

Ethanoyl chloride reacts with cold conc. solution of ethylamine. Mixture of N-ethylethanamide ( an N-substituted amide) and ethylammonium chloride

Question 13

What happens If hydrogen chloride and ethylamine react

Answer 13

If hydrogen chloride and ethylamine react: ethylammonium chloride is formed

Question 14

Describe the first stage of reaction between ethylamine and ethanol chloride

Answer 14

First stage involves a nucleophilic attack on fairly positive carbon atom by lone pair in the nitrogen atom in ethylamine

Question 15

Describe the second stage of reaction between ethaylamine and ethanol chloride

Answer 15

Second stage is elimination stage which happens in two steps
First the carbon-oxygen double bond reforms and a chloride ion is pushed off

Question 16

What are carbonyl group, aldehyde group and ketone group

Answer 16

Question 17

Describe the difference between reflux and distillation apparatus

Answer 17

• Reflux is a technique
  used in chemical
  laboratories to dissolve
  components that are hard
  to be dissolved
• Distillation is the action
  of purifying a liquid by
  the process of heating
  and cooling
• Reflux Purpose is to dissolve
  components in a reaction
  mixture that are hard to be
  dissolved and to complete
  to chemical reaction
• Distillation Purpose is to separate
  different components in
  a mixture
• Reflux Apparatus is composed of
  a round-bottomed flask, a
  condenser. a water bath
  and heat source
• Distillation Apparatus is composed of
  a round-bottomed flask
  connected to a Y adapter
  which is connected to a
  condenser attached to a
  receiving flask

Question 18

How can you make amines

Answer 18

from nitriles or halogenoalkanes

Question 19

How do you make propylamine from reduction

Answer 19

Reducing nitriles via LiAl4 in dry ether
or
The reduction of nitriles using hydrogen and a metal catalyst (Pd catalyst)

Question 20

What are the equations of reducing nitriles to make propylamine

Answer 20

With LiAl4 in dry ether:
CH3CH2CN + 4[H] → CH3CH2CH2NH2
With hydrogen and Pd catalyst:
CH3CH2CN + 2H2 → CH3CH2CH2NH2

Question 21

Give the reagent and essential conditions for the formation of propylamine from a halogenoalkane.

Answer 21

• ethanolic/alcoholic
  ammonia
• heat and under pressure

Question 22

Compare and contrast the structures, optical activity and reactions with acids and bases of alanine and glycine.
Include diagrams, structures and equations to illustrate your answer.

Answer 22

Similarities
They are both zwitterions:
NH3+CH(CH3)COO− / NH3+CH2COO−
Reaction with acid:
H+ + NH3+CH2COO− → NH3+CH2COOH or
H+ + NH3+CH(CH3)COO− → H3N+CH(CH3)COOH

Reaction with a base:
OH−+NH3+CH2COO−→NH2CH2COO−+H2O or OH−+NH3+CH(CH3)COO−→NH2CH(CH3)COO−+H2O

alanine has a chiral centre/ asymmetric
carbon atom/ non-superimposable mirror images
and
glycine does not

• (an aqueous solution of) alanine rotates the
  plane (of polarisation) of plane-polarised
  (monochromatic) light but glycine does not

Question 23

Explain the difference in the volumes of 0.010 mol dm–3 hydrochloric acid required to completely react with separate 10.0 cm3 samples of aqueous lysine and of aqueous serine, both of concentration 0.010 mol dm–3.

Answer 23

• lysine requires twice (the volume of HCl) (1)
• (because) lysine has two (basic) amine/NH2 groups whereas serine has one

Question 24

how do you make an ester

Answer 24

carboxylic acid and alcohol w conc. H2SO4 catalyst
or acyl chloride and alcohol:
If you add an acyl chloride to an alcohol, you get a vigorous (even violent) reaction at room temperature producing an ester and clouds of steamy acidic fumes of hydrogen chloride.

Question 25

) Esters can be hydrolysed by heating under reflux with aqueous acid or alkali. Compare and contrast these two methods of hydrolysis for amyl acetate.

Answer 25

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