EDEXEL A LEVE CHEMISTRY EXAM ACTUAL QUESTIONS
AND CORRECT ANSWERS ALREADY GRADED A+
GUARANTEED SUCCESS
Hydrogenation
Hydrogen is added to an alkene in the presence of a nickel catalyst to produce an alkane
The hydrogenation of saturated vegetable oils is used to make margarine
Halogenation
Halogens are added to alkenes under no specific conditions to produce halogenoalkanes.
This is used to test whether a compound is an alkene or alkane as an alkene will react with Br in
Bromine water to turn it colorless.
Hydration
Water (in the form of steam) is added to an alkene is the presence of Phosphoric acid (H3PO4) to
produce alcohols
Addition of Hydrogen Halides
Hydrogen halides are added under no specific conditions and form a halogenoalkane
Oxidation to diols
Water and an oxygen from the oxygen agent (depicted as [O]) Potassium manganate (VII)
(KMnO4) is added to an alkene in acidic conditions to produce a diol
Heterolytic fission
The heterolytic fission of a covalent bond results in two ions being formed as one of the atoms
takes the electrons
Mechanism of Electrophilic additions
As the Cl2 approaches the ethene, a temporary dipole is set up due to the high electron density of
the double bond.
The Cl+ ion reacts with the ethene, opening the double bond and leaving a carbocation.
This then reacts with the Cl- ion
The same process can occur with hydrogen halides, but in that case the H already has a slight
positive charge
1
,Mechanism of Electrophilic additions:
Unsymmetrical molecules
In an unsymmetrical alkene, there are two possible products.
The Major product will always be formed from the more stable carbocation.
Primary, Secondary and Tertiary Carbocations
Primary carbocations are when the positive carbocation is only next to one other carbon, Secondary
when it is next to two other carbons and tertiary when it is next to three.
As the carbons c=sharethe positive charge, secondary carbocations are more stable than primary
ones, and tertiary are more stable than secondary
Polymer
A long molecule consisting of many similar or identical monomers linked together.
monomer
A simple compound whose molecules can join together to form polymers
The group 2 element is heated with chlorine gas
Group 2 reactions with water
M(s) + 2H₂O(l) -> M(OH)₂(aq) + H2(g)
Magnesium reacts very slowly with water, calcium, strontium and barium do so with increasing
vigor.
Trends of solubility of group 2 hydroxides
Solubility increases down the group as calcium hydroxide is only slightly soluble, so watch out
for the state symbol change between calcium and strontium.
PH value of these alkaline solutions depends not only on concentration but also on the solubility
of the hydroxide.
Reactions of group 2 oxides
MO(s) + H₂O(l) -> M(OH)₂(aq)
A group 2 oxide reacts with water to form an alkali
They also react with dilute acids in neutralisation reactions (as do hydroxides)
Testing for carbon dioxide
2
, When carbon dioxide is passed through limewater (saturated aqueous solution of calcium
hydroxide) it reacts with the calcium hydroxide to form calcium carbonate, a white precipitate that
makes the solution go cloudy.
CO2 + Ca(OH)2 -> CaCO3 + H2O
Milk of Magnesia
Milk of Magnesia is a suspension of magnesium hydroxide in water and is used as an antacid as
the OH ions neutralise the HCl in the stomach. OH ions can damage stomach lining, but
Magnesium hydroxides low solubility means that there are few hydroxide ions in the solution.
Trends of solubility of group 2 sulphates
All group 2 nitrates and chlorides are soluble, but the solubility of sulphates decreases down the
group. Calcium sulphate is slightly soluble, strontium and barium sulphate are completely
insoluble.
Barium Meals
Barium sulphate is given to patients so that softer tissues show up on an x-ray. Barium ions are
harmful to humans, but as barium sulphate is insoluble, the ions are not free to move
Test for sulphate ions
Add barium chloride (as the barium sulphate subsequently formed is insoluble and thus a white
precipitate). Also add a dilute acid (such as nitric acid) to prevent other compounds such as barium
carbonate being formed as a white precipitate.
Thermal stability
a measure of the extent to which a compound decomposes when heated
Reasons for trends in thermal stability of group 1 and group 2 nitrates and carbonates
Group 2 are less thermally stable than group 1 because the ions have a larger charge.
The further up the group the greater the charge density as the ionic radius is smaller, so the ion is
more polarising so it distorts the ion more, making it less thermally stable .
Nitrates and carbonates thermally decompose as they consist of more complex ions that can
decompose to a stabler form.
Thermal decomposition of group 1 and 2 nitrates
Lithium and all other group 2 nitrates undergo greater decomposition:
4LiNO3 -> 2Li2O + 4NO2 + O2
2Mg(NO3)2 -> 2MgO + 4NO2 + O2
Brown fumes (from NO2) can be seen in this reaction.
3
AND CORRECT ANSWERS ALREADY GRADED A+
GUARANTEED SUCCESS
Hydrogenation
Hydrogen is added to an alkene in the presence of a nickel catalyst to produce an alkane
The hydrogenation of saturated vegetable oils is used to make margarine
Halogenation
Halogens are added to alkenes under no specific conditions to produce halogenoalkanes.
This is used to test whether a compound is an alkene or alkane as an alkene will react with Br in
Bromine water to turn it colorless.
Hydration
Water (in the form of steam) is added to an alkene is the presence of Phosphoric acid (H3PO4) to
produce alcohols
Addition of Hydrogen Halides
Hydrogen halides are added under no specific conditions and form a halogenoalkane
Oxidation to diols
Water and an oxygen from the oxygen agent (depicted as [O]) Potassium manganate (VII)
(KMnO4) is added to an alkene in acidic conditions to produce a diol
Heterolytic fission
The heterolytic fission of a covalent bond results in two ions being formed as one of the atoms
takes the electrons
Mechanism of Electrophilic additions
As the Cl2 approaches the ethene, a temporary dipole is set up due to the high electron density of
the double bond.
The Cl+ ion reacts with the ethene, opening the double bond and leaving a carbocation.
This then reacts with the Cl- ion
The same process can occur with hydrogen halides, but in that case the H already has a slight
positive charge
1
,Mechanism of Electrophilic additions:
Unsymmetrical molecules
In an unsymmetrical alkene, there are two possible products.
The Major product will always be formed from the more stable carbocation.
Primary, Secondary and Tertiary Carbocations
Primary carbocations are when the positive carbocation is only next to one other carbon, Secondary
when it is next to two other carbons and tertiary when it is next to three.
As the carbons c=sharethe positive charge, secondary carbocations are more stable than primary
ones, and tertiary are more stable than secondary
Polymer
A long molecule consisting of many similar or identical monomers linked together.
monomer
A simple compound whose molecules can join together to form polymers
The group 2 element is heated with chlorine gas
Group 2 reactions with water
M(s) + 2H₂O(l) -> M(OH)₂(aq) + H2(g)
Magnesium reacts very slowly with water, calcium, strontium and barium do so with increasing
vigor.
Trends of solubility of group 2 hydroxides
Solubility increases down the group as calcium hydroxide is only slightly soluble, so watch out
for the state symbol change between calcium and strontium.
PH value of these alkaline solutions depends not only on concentration but also on the solubility
of the hydroxide.
Reactions of group 2 oxides
MO(s) + H₂O(l) -> M(OH)₂(aq)
A group 2 oxide reacts with water to form an alkali
They also react with dilute acids in neutralisation reactions (as do hydroxides)
Testing for carbon dioxide
2
, When carbon dioxide is passed through limewater (saturated aqueous solution of calcium
hydroxide) it reacts with the calcium hydroxide to form calcium carbonate, a white precipitate that
makes the solution go cloudy.
CO2 + Ca(OH)2 -> CaCO3 + H2O
Milk of Magnesia
Milk of Magnesia is a suspension of magnesium hydroxide in water and is used as an antacid as
the OH ions neutralise the HCl in the stomach. OH ions can damage stomach lining, but
Magnesium hydroxides low solubility means that there are few hydroxide ions in the solution.
Trends of solubility of group 2 sulphates
All group 2 nitrates and chlorides are soluble, but the solubility of sulphates decreases down the
group. Calcium sulphate is slightly soluble, strontium and barium sulphate are completely
insoluble.
Barium Meals
Barium sulphate is given to patients so that softer tissues show up on an x-ray. Barium ions are
harmful to humans, but as barium sulphate is insoluble, the ions are not free to move
Test for sulphate ions
Add barium chloride (as the barium sulphate subsequently formed is insoluble and thus a white
precipitate). Also add a dilute acid (such as nitric acid) to prevent other compounds such as barium
carbonate being formed as a white precipitate.
Thermal stability
a measure of the extent to which a compound decomposes when heated
Reasons for trends in thermal stability of group 1 and group 2 nitrates and carbonates
Group 2 are less thermally stable than group 1 because the ions have a larger charge.
The further up the group the greater the charge density as the ionic radius is smaller, so the ion is
more polarising so it distorts the ion more, making it less thermally stable .
Nitrates and carbonates thermally decompose as they consist of more complex ions that can
decompose to a stabler form.
Thermal decomposition of group 1 and 2 nitrates
Lithium and all other group 2 nitrates undergo greater decomposition:
4LiNO3 -> 2Li2O + 4NO2 + O2
2Mg(NO3)2 -> 2MgO + 4NO2 + O2
Brown fumes (from NO2) can be seen in this reaction.
3
