The halogens are good oxidising agents - Leaving Cert Chemistry - Question c - 2007
Question c
The halogens are good oxidising agents.
(i) How does the oxidation number of the oxidising agent change during a redox reaction?
(ii) Assign oxidation numbers in e... show full transcript
Worked Solution & Example Answer:The halogens are good oxidising agents - Leaving Cert Chemistry - Question c - 2007
Step 1
How does the oxidation number of the oxidising agent change during a redox reaction?
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Answer
In a redox reaction, the oxidation number of the oxidising agent decreases. This occurs because the oxidising agent gains electrons, resulting in a lower oxidation state as it is reduced.
Step 2
Assign oxidation numbers in each of the following equations to show clearly that the halogen is the oxidising agent in each case.
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Answer
1st equation:
Oxidation number of Br in Br₂ = 0
Oxidation number of Br in Br⁻ = -1
2nd equation:
Oxidation number of Cl in Cl₂ = 0
Oxidation number of Cl in Cl⁻ = -1
Step 3
Hence or otherwise balance the second equation.
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Balancing the second equation:
Cl₂ + SO₄²⁻ + H₂O → 2Cl⁻ + SO₄²⁻ + 2H⁺
The balanced equation maintains the same number of atoms for each element on both sides, ensuring conservation of mass.
Step 4
Why does the oxidising ability of the halogens decrease down the group?
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The oxidising ability of the halogens decreases down the group due to the increasing atomic radius (size), which leads to an increase in the number of electron shells. This increase results in greater shielding (screening) of the nucleus, diminishing the electronegativity, or the attraction for electrons, making it less effective as an oxidising agent.
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