A-LEVEL JUNE 2024 OCR CHEMISTRY A PAPER
1 WITH QUESTIONS AND THEIR COMPLETE
SOLUTIONS
What two types of bond are within an alkene? - Correct Answer-✔✔sigma and pi
sigma bond - Correct Answer-✔✔the direct overlapping of two orbitals
pi bond - Correct Answer-✔✔the sideways overlap of p orbitals
C=C how many pi bonds and sigma bonds are in this - Correct Answer-✔✔one sigma
two pi bonds
what two types of isomers are found in alkenes - Correct Answer-✔✔cis/trans and
E/Z
Difference between E/Z isomers and Cis/trans isomers - Correct Answer-✔✔E/Z
compares relative position based in priority groups (IP rules) look at the atomic
number of the first bonded element
Cis/Trans compares the relative positions of identical groups
major and minor products in alkenes - Correct Answer-✔✔the major product forms
the most stable carbocation intermediate during alkene reactions
tertiary>secondary>primary
,what type of polymer do alkenes produce? - Correct Answer-✔✔addition polymers
synthesis of an organic liquid - Correct Answer-✔✔once reaction is complete into a
separating funnel. Neutralise any excess acid using sodium carbonate (stops bubbling
when all gone)
Allow 2 layers to settle
Use density into to establish layers. If density into not given, add water to establish
aqueous layer.
(aqueous layer get bigger)
Density of water is 1 anything greater is more dense.
collect the organic layer
add a drying agent to remove small traces of water left in the organic layer (e.g..
anhydrous CaCl2)
If the question tells you the boiling point of the organic liquid say distil dried product
and collect fraction that comes over the boiling point.
3 ways to determine purity of products - Correct Answer-✔✔1. boiling point should
match known data, boils over a narrow range
or
2. Run TLC, measure Rf value, compare to known data values/Run TLC and compare to
chromatogram of pure sample
or
3. Run NMR/IR/Mass spectrum, compare to spectral database of pure compounds.
How to purify by recrystallisation? - Correct Answer-✔✔-dissolve in a minimum
volume of hot solvent
,-cool in ice to recrystallise (impurities stay in solution)
-filter using Büchner flask/reduced pressure filtration
-wash with cold solvent
-dry
Does reflux have an open or closed system? - Correct Answer-✔✔open
overall equation for ozone depletion - Correct Answer-✔✔O3 + O -> 2O2
rate of formation of ozone = - Correct Answer-✔✔rate of breakdown of ozone by UV
light =
what type of compound breaks down the ozone layer? - Correct Answer-
✔✔chlorofluorocarbons
Initiation reaction of CCl3F
what is the mechanism, equation and why the radicals formed - Correct Answer-
✔✔homolytic bond fission
Cl. + CCl2F.
C-Cl bond broken as its weaker than C-F
Evidence for the structure of delocalised benzene against the kekule structure -
Correct Answer-✔✔-Bond lengths of benzene are the same
-enthalpy of hydrogenation less exothermic than expected
, -does not undergo addition reaction
why does benzene need a halogen carrier to undergo electrophilic subsitution? -
Correct Answer-✔✔it is not electron dense enough to polarize the molecule into an
electrophile
electrophile - Correct Answer-✔✔electron pair acceptor
what is the catalyst for halogenation of benzene? - Correct Answer-✔✔AlX3
what is the catalyst for nitration of benzene? - Correct Answer-✔✔sulfuric acid
How can you test for a phenol? - Correct Answer-✔✔weak acid that reacts with
NaOH but too weak to react with Na2CO3 so no bubbles of CO2
why don't you need a catalyst for the halogenation and nitration of phenol? - Correct
Answer-✔✔The lone pair on the oxygen molecule in the hydroxyl group donates its
pair of electrons into the delocalised pi ring. Increases the electron density of the
phenol molecule which allows phenol to polarise HNO3 and X2 molecules to produce
an electrophile
what is the colour change when phenol is halogenated with Bromine molecule? -
Correct Answer-✔✔Br2 is decolourised and a white ppt is formed.
1 WITH QUESTIONS AND THEIR COMPLETE
SOLUTIONS
What two types of bond are within an alkene? - Correct Answer-✔✔sigma and pi
sigma bond - Correct Answer-✔✔the direct overlapping of two orbitals
pi bond - Correct Answer-✔✔the sideways overlap of p orbitals
C=C how many pi bonds and sigma bonds are in this - Correct Answer-✔✔one sigma
two pi bonds
what two types of isomers are found in alkenes - Correct Answer-✔✔cis/trans and
E/Z
Difference between E/Z isomers and Cis/trans isomers - Correct Answer-✔✔E/Z
compares relative position based in priority groups (IP rules) look at the atomic
number of the first bonded element
Cis/Trans compares the relative positions of identical groups
major and minor products in alkenes - Correct Answer-✔✔the major product forms
the most stable carbocation intermediate during alkene reactions
tertiary>secondary>primary
,what type of polymer do alkenes produce? - Correct Answer-✔✔addition polymers
synthesis of an organic liquid - Correct Answer-✔✔once reaction is complete into a
separating funnel. Neutralise any excess acid using sodium carbonate (stops bubbling
when all gone)
Allow 2 layers to settle
Use density into to establish layers. If density into not given, add water to establish
aqueous layer.
(aqueous layer get bigger)
Density of water is 1 anything greater is more dense.
collect the organic layer
add a drying agent to remove small traces of water left in the organic layer (e.g..
anhydrous CaCl2)
If the question tells you the boiling point of the organic liquid say distil dried product
and collect fraction that comes over the boiling point.
3 ways to determine purity of products - Correct Answer-✔✔1. boiling point should
match known data, boils over a narrow range
or
2. Run TLC, measure Rf value, compare to known data values/Run TLC and compare to
chromatogram of pure sample
or
3. Run NMR/IR/Mass spectrum, compare to spectral database of pure compounds.
How to purify by recrystallisation? - Correct Answer-✔✔-dissolve in a minimum
volume of hot solvent
,-cool in ice to recrystallise (impurities stay in solution)
-filter using Büchner flask/reduced pressure filtration
-wash with cold solvent
-dry
Does reflux have an open or closed system? - Correct Answer-✔✔open
overall equation for ozone depletion - Correct Answer-✔✔O3 + O -> 2O2
rate of formation of ozone = - Correct Answer-✔✔rate of breakdown of ozone by UV
light =
what type of compound breaks down the ozone layer? - Correct Answer-
✔✔chlorofluorocarbons
Initiation reaction of CCl3F
what is the mechanism, equation and why the radicals formed - Correct Answer-
✔✔homolytic bond fission
Cl. + CCl2F.
C-Cl bond broken as its weaker than C-F
Evidence for the structure of delocalised benzene against the kekule structure -
Correct Answer-✔✔-Bond lengths of benzene are the same
-enthalpy of hydrogenation less exothermic than expected
, -does not undergo addition reaction
why does benzene need a halogen carrier to undergo electrophilic subsitution? -
Correct Answer-✔✔it is not electron dense enough to polarize the molecule into an
electrophile
electrophile - Correct Answer-✔✔electron pair acceptor
what is the catalyst for halogenation of benzene? - Correct Answer-✔✔AlX3
what is the catalyst for nitration of benzene? - Correct Answer-✔✔sulfuric acid
How can you test for a phenol? - Correct Answer-✔✔weak acid that reacts with
NaOH but too weak to react with Na2CO3 so no bubbles of CO2
why don't you need a catalyst for the halogenation and nitration of phenol? - Correct
Answer-✔✔The lone pair on the oxygen molecule in the hydroxyl group donates its
pair of electrons into the delocalised pi ring. Increases the electron density of the
phenol molecule which allows phenol to polarise HNO3 and X2 molecules to produce
an electrophile
what is the colour change when phenol is halogenated with Bromine molecule? -
Correct Answer-✔✔Br2 is decolourised and a white ppt is formed.
