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Title: detailed notes
Description: CAIE AS level notes lesson -chemistry group 2 syllabus 2025-2027
Description: CAIE AS level notes lesson -chemistry group 2 syllabus 2025-2027
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CIE A Level Chemistry
10
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Reactions of Group 2 Elements
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Reactions of the Group 2 Elements
The Group 2 elements react with oxygen, water and dilute acids
Reaction of Group 2 elements table
Group 2
element
Reaction with
oxygen
Reaction with water
Mg
Burns easily
Bright white flame
Vigorous reaction
with steam
Very slow reaction
with water
Ca
Difficult to ignite
Red flame
Reacts moderately
Hydroxide formed
Sr
Difficult to ignite
Red flame
Reacts rapidly
Hydroxide formed
Ba
Difficult to ignite
Green flame
Reacts vigorously
Hydroxide formed
Reaction with dilute
Reaction with dilute H2SO4
HCl
Reacts vigorously
Reacts vigorously
Reaction is slowed by the
formation of a sparingly
soluble sulfate layer which
Reacts vigorously
coats the metal surface
stopping hydrogen bubbles
from rising
Reaction is quickly stopped by
the formation of an insoluble
Reacts vigorously
sulfate layer on the metal
surface
Reaction is quickly stopped by
the formation of an insoluble
Reacts vigorously
sulfate layer on the metal
surface
Group 2 reactions with oxygen & water chemical equations
Group 2
element
Reaction with oxygen
Reaction with water
Mg
2Mg (s) + O2 (g) → 2MgO (s)
Mg (s) + H2O (l) → Mg(OH)2 (s) + H2 (g) *
Ca
2Ca (s) + O2 (g) → 2CaO (s)
Ca (s) + 2H2O (l) → Ca(OH)2 (s) + H2 (g)
Sr
2Sr (s) + O2 (g) → 2SrO (s)
Sr (s) + O2 (g) → SrO2 (s)
Sr (s) + 2H2O (l) → Sr(OH)2 (aq) + H2 (g)
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Examiner Tip
Learn the general equation for the reaction with oxygen, water and dilute HCl / H2SO4 and the
exceptions instead of memorizing the entire table!
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0) is formed
CaO
CaO (s) + H2O (l) → Ca(OH)2 (s)
A vigorous reaction which releases a lot of
energy, causing some of the water to boil off as
the solid lump seems to expand and open (pH
11
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Group 2
element
Reaction with dilute HCl
Reaction with dilute H2SO4
Mg
Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g)
Ca
Ca (s) + 2HCl (aq) → CaCl2 (aq) + H2 (g)
Ca (s) + H2SO4 (aq) → CaSO4 (aq) + H2 (g)
Sr
Sr (s) + 2HCl (aq) → SrCl2 (aq) + H2 (g)
Sr (s) + H2SO4 (aq) → SrSO4 (s) + H2 (g)
Ba
Ba (s) + 2HCl (aq) → BaCl2 (aq) + H2 (g)
Ba (s) + H2SO4 (aq) → BaSO4 (s) + H2 (g)
When some Group 2 metals react with sulfuric acid rather than hydrochloric, an insoluble sulfate forms
Going down the group, the Group 2 sulfates become less and less soluble
Calcium sulfate is sparingly soluble, but strontium sulfate and barium sulfate are insoluble
Reactions of Group 2 oxides with acid
Group 2 sulfates also form when a Group 2 oxide is reacted with an acid
The insoluble sulfates form at the surface of the oxide, which means that the solid oxide beneath it
can’t react with the acid
This can be prevented to an extent by using the oxide in powder form and stirring, in which case
neutralisation can take place
Remember that:
oxide + dilute hydrochloric acid → salt + water
oxide + dilute sulfuric acid → sulfate + water
Reactions of group 2 hydroxides
The Group 2 metal hydroxides form colourless solutions of metal chlorides when they react with a
dilute acid
The sulfates decrease in solubility going down the group (barium sulfate is an insoluble white
precipitate)
Group 2 hydroxide reactions with dilute acids table
Group 2
hydroxide
Reaction with dilute HCl
Reaction with dilute H2SO4
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Remember that:
carbonate + dilute hydrochloric acid → salt + water + carbon dioxide
carbonate + dilute sulfuric acid → sulfate + water + carbon dioxide
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The more polarised they are, the more likely they are to thermally decompose as the bonds in the
carbonate and nitrate ions become weaker
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The graph shows that both the first and second ionisation energies decrease going down the table
The first ionisation energy is the energy needed to remove the first outer electron of an atom
The second ionisation energy is the energy needed to remove the second outer electron of an atom
The graph above shows that going down the group, it becomes easier to remove the outer two
electrons of the metals
Though the nuclear charge on the nucleus increases going down the group (because there are more
protons), factors such as an increased shielding effect and a larger distance between the outermost
electrons and the nucleus outweigh the attraction of the higher nuclear charge
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The graph shows a increase in atomic radius going down the group
The melting point of the elements decreases going down the group as the outer electrons get further
away from the nucleus
This means that the attraction between the nucleus and the bonding electrons decreases causing a
decrease in melting point
Graph of the melting points descending Group 2
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The graph shows an overall increase in density going down the group
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Applying your knowledge of the Group 2 elements, predict:
1
...
2
...
3
...
4
...
5
...
6
...
7
...
8
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Answer
Answer 1:
Since Ra is in Group 2, it will form an ion with a +2 charge to give Ra2+
Answer 2:
The Group 2 oxides and hydroxides have the general formula XO and X(OH)2 respectively,
where X is the Group 2 element
Therefore, radium oxide is RaO and radium hydroxide is Ra(OH)2
Answer 3:
Radium is below barium so its atomic radius is larger than the atomic radius of barium
...
The first ionisation energy is between 450 - 480 kJ mol-1
Answer 4:
Radium’s outermost electrons are even further away than in barium and are therefore more
easily removed making radium more reactive than barium
Answer 5:
The Group 2 hydroxides become more soluble going down the group
Radium hydroxide will therefore be more soluble than calcium hydroxide
Answer 6:
The Group 2 sulfates become less soluble going down the group
Radium sulfate will therefore be less soluble than strontium sulfate
Answer 7:
The general equation for the reaction of Group 2 oxides with dilute hydrochloric acid is:
XO (s) + 2HCl (aq) → XCl2 (aq) + H2O (l)
where X is the Group 2 element
The reaction of radium oxide with dilute hydrochloric acid is therefore:
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Trends in Solubility of Group 2 Hydroxides & Sulfates
Trends in Solubility of Group 2 Hydroxides & Sulfates
Group 2 hydroxides
Going down the group, the solutions formed from the reaction of Group 2 oxides with water become
more alkaline
When the oxides are dissolved in water, the following ionic reaction takes place:
O2- (aq) + H2O(l) → 2OH- (aq)
The higher the concentration of OH- ions formed, the more alkaline the solution
The alkalinity of the formed solution can therefore be explained by the solubility of the Group 2
hydroxides
Solubility of the Group 2 hydroxides table
Group 2 hydroxide
Solubility at 298 K
(mol / 100 g of water)
Mg(OH)2
2
...
5 x 10–3
Sr(OH)2
3
...
5 x 10–2
The hydroxides dissolve in water as follows:
X(OH)2 (aq) → X (aq) + 2OH– (aq)
Where X is the Group 2 element
When the metal oxides react with water, a Group 2 hydroxide is formed
Going down the group, the solubility of these hydroxides increases
This means that the concentration of OH- ions increases, increasing the pH of the solution
As a result, going down the group, the alkalinity of the solution formed increases when Group 2 oxides
react with water
The solubility of the Group 2 hydroxides
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Going down the group, the solubility of the sulfates decreases
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Title: detailed notes
Description: CAIE AS level notes lesson -chemistry group 2 syllabus 2025-2027
Description: CAIE AS level notes lesson -chemistry group 2 syllabus 2025-2027