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Wrong Past paper questions > Chem P2 > Flashcards

Chem P2 Flashcards

1
Q

The compound flavan-3-ol is found in tea, fruit and wine.
*A sample of flavan-3-ol extracted from wine contained some ethanol. The sample
was left in a flask, open to the air for several days. The contents were then analysed
to identify any new compounds formed. Several new compounds were found to be
present, including some with a distinctive fruity smell.
Identify four new organic compounds that could form under these conditions
by considering the chemistry of alcohols. Justify your answers. Include the
structure of two compounds formed from flavan-3-ol, one of which has a fruity smell.
(6)

A
  • ethanol can be oxidised
  • which can form ethanoic acid
  • ethanoic acid can further oxidise to form ethanal
  • Flavan-3-ol can oxidise to form flavann-3-one
  • ethanoic acid and ethanol can react together to from ethyl ethanoate
  • (structure of flavan-3-one)
  • (structure of ester formed by flavan-3-one and ethanoic acid)
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2
Q

The table contains data on propanone and ethanoic acid.
(ethanoic acid has higher boiling temp)
(both are completely miscible in water)
Molar mass Ethanoic acid: 60
Molar mass propanone 58
(i) Explain, by reference to the data and any intermolecular forces involved, the difference in
the boiling temperatures.

A
  • both have similar molar masses so similar mag of london forces
  • ethanoic acid can form h bonds.
  • propanone can only form permanent dipoles dipole
  • so H bonds take more energy to break.
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3
Q

Esters have many uses due to their characteristic aromas and often have common names.
For example, isoamyl acetate is referred to as banana oil and amyl acetate has a scent
similar to apples.
Esters can be hydrolysed by heating under reflux with aqueous acid or alkali.
Compare and contrast these two methods of hydrolysis for amyl acetate.
(4)

A
  • both will make the same alcohol
  • acid hydrolysis reaction is reversible, but alkali hydrolysis goes to completion
  • Alkalai hydrolysis will produce ethanoate ion/ salt acid hydrolysis will produce the carbocxyllic acid
  • Acid is the catalyst for acid hydrolysis, but alklai is a reactant.
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4
Q

) In an experiment, the crystals are filtered, weighed and the percentage yield calculated.
Student 1 obtained a yield of 102.6%.
Student 2 obtained a yield of 56.4%.
The expected yield is 82% and the students carried out the calculation correctly.
Discuss possible reasons for the yields obtained by these students.
(4)

A

Reasons for student 1:
- crystals were still wet when weighed - not fully dried
- thus mass measured was much higher
- there may have been impurities in the crystal
Reasons for student 2:
- mass of crystals may have been lost due to some crystals remaining in filter paper during filtration
- reaction may have been incomplete
- crystals may have not fully crystilise d

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5
Q

State why HOOCCH==CHCOOH has E/Z isomers.
(2)

A
  • limited rotation about the c=c bond
  • so each carbon in double bond is attached to 2 different groups
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6
Q

Explain what is meant by the term stereoisomers

A
  • same structural formula
  • but diff arrangement of atoms in space
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7
Q

What reagent and conditions is used to convert a dicarboxylic acid into a diol?

A
  • LiAlH4 in dry ether
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8
Q

give two reasons why it is not a good idea to produce a halogenoalkane from chlorine and alkane in presence of UV light

A
  • many side products can form
  • will need to separate the haloalkane from everything.
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9
Q

Explain the trend in reactivity of the primary chloro-, bromo- and iodoalkanes
with aqueous hydroxide ions.
(2)

A
  • gets more reactive down the group
  • because C-X bond gets weaker down the group
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10
Q

The bromination of the benzene ring in paracetamol occurs much more readily
compared to the bromination of benzene.
Explain this increased reactivity. (2)

A
  • lone pair from Oxygen interacts with delocalised ring of electrons.
  • this makes it more susceptible to electrophilic attack.
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11
Q

Explain why the honeycomb structure is used in a car exhaust system.
(2)

A
  • provides larger SA
  • allows gases to flow between
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12
Q

The third reaction in the airbag is between the metal oxides and silicon dioxide.
State the type of reaction taking place and justify why this reaction is necessary.
(3)

A
  • this is an acid base reaction
  • metal oxides are corrosive
  • whereas salts formed are unreactive
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13
Q

What is the change in shape of the Maxwell Boltzman curve when the airbag cools?
(1)
A the peak would shift to the left and be higher
B the peak would shift to the left and be lower
C the peak would shift to the right and be higher
D the peak would shift to the right and be lower

A

A

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14
Q

Using the apparatus for distillation instead of reflux is not an efficient way to
produce ethanoic acid from ethanol. Explain why.
(2)

A
  • ethanol would be oxidised to ethanal
  • ethanal is very volatile
  • so ethanal will be distilled off before ethanoic acid is formed.
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15
Q

Devise an experiment, giving outline details only, that would enable the relative
rates of hydrolysis of halogenoalkanes to be compared.
(5)

A
  • dissolve halogenoalkanes in ethanol as a solvent
  • using same amounts of each halogenoalkane.
  • add in few drops of silver nitrate to solutions
  • measure time taken for ppt to form.
  • use a water bath to control temperature
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16
Q

Compare and contrast the bromination of phenol with the bromination of benzene.
(3)

A
  • both are electrophillic sub reactions
  • bromination of benzene needs to be heated under reflux, but phenol doesn’t - needs room temp.
  • Phenol goes through multiple sub reactions whereas benzene goes through only one
17
Q

State why the order of reaction with respect to iodide ions cannot be five, even
though 5mol of iodide ions are shown in the equation.

A
  • the chances of 5 or more ions colliding in the RDS is negligible
18
Q

Explain why P can form PCl5 but nitrogen cannot form NCl5

A
  • P can expand its outer shell
  • but Nitrogen can only accommodate 8 electrons in its outer shell.
19
Q

explain why NCl3 has a higher boiling point than NF3 (5)

A
  • NCl3 has more magnitude of London Forces
  • because Cl has more electrons
  • but NF3 has stronger permanent dipole-dipole
  • because electronegativity difference between N and F is greater than N and Cl
  • but London Forces outweigh permanent dipole-dipoles
20
Q

Why is phenol more reactive than benzene

A
  • lone pair on Oxygen interacts with delocalised electron ring
  • which increases the electron density of the ring
  • this makes it more vulnerable to electrophillic attack
21
Q

explain why impurities in a heterogenous catalyst will result in the catalyst being less effective

A
  • the impurities will occupy the active sites
  • which will prevent bond weaking in reactants
  • meaning that there is a lower chance that the impurities will desorb from the catalyst surface.
22
Q

LiAlH4 is a source of hydride ions, H−
.
Give a possible reason why LiAlH4 cannot be used to reduce alkenes.
(1)

A
  • because it will be repelled by the way Pi bond in alkenes
23
Q

Explain why 2,2-dimethylpropane has a much lower boiling temperature than its
isomer pentane.
Detailed descriptions of the forces involved are not required.
(2)

A
  • is branched, so London forces are weaker
  • due to a larger SA
24
Q

give a reason why nitrogen is used in crisp bags and not air

A
  • because it prevents the oxidation of the crisps
25
Q

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.
(4)

A
  • Nucleophile is an electron pair donor
  • so butylamine acts as one by attacking the delta+ C on the acyl chloride
  • which produces HCl
  • and a base is a proton acceptor
26
Q

Explain why the use of this apparatus would give a very low yield of propanal.
(2)

A
  • apparatus is refluxed
  • so propanal will be just further oxidised to propanoic acid
27
Q

) When propene reacts with a mixture of bromine and sodium chloride, it forms
1,2-dibromopropane, 1-bromo-2-chloropropane and 2-bromo-1-chloropropane
but no 1,2-dichloropropane.
explain why with ref to its mechanism

A
  • first step involves a electrophile, and Cl- is not an electrophile
  • and so Br- must attack first
28
Q

Explain why far more 1-bromo-2-chloropropane forms than
2-bromo-1-chloropropane

A
  • because a secondary carbocation forms
  • which is much more stable than a primary
29
Q

Explain why P can form PCl5 but N cannot form NCl5

A
  • P can expand its octet, so it can hold only 8 electrons in its outer shell
  • N however can only hold 8.

Wrong Past paper questions (6 decks)

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