Define reduction in terms of (i) electron transfer, (ii) change in oxidation number. (iii) The oxidation number of hydrogen in most of its compounds is +1. Explain why the oxidation number of hydrogen in the metal hydrides is -1. (iv) The oxidation number of oxygen in most of its compounds is -2. What is the oxidation number of oxygen in OF2? (v) The following unbalanced equation describes a reaction that occurs in aqueous solution. Mn²⁺ + BiO₃⁻ + H⁺ → MnO₄⁻ + Bi³⁺ + H₂O Assign oxidation numbers and, hence or otherwise, balance this equation. (vi) Identify the reducing agent in the reaction above.

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Define reduction in terms of (i) electron transfer, (ii) change in oxidation number - Leaving Cert Chemistry - Question 11 - 2022

Question 11

Define reduction in terms of (i) electron transfer, (ii) change in oxidation number. (iii) The oxidation number of hydrogen in most of its compounds is +1. Explai... show full transcript

Worked Solution & Example Answer:Define reduction in terms of (i) electron transfer, (ii) change in oxidation number - Leaving Cert Chemistry - Question 11 - 2022

Step 1

Define reduction in terms of (i) electron transfer

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Answer

Reduction is defined as the gain of electrons by a species during a chemical reaction. This means that when a substance is reduced, it acquires electrons, leading to a decrease in its oxidation state.

Step 2

Define reduction in terms of (ii) change in oxidation number

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Answer

Reduction also involves a decrease in the oxidation number of an atom in a molecule. This occurs when an atom gains electrons, resulting in a lower positive charge or a more negative charge.

Step 3

Define reduction in terms of (iii) oxidation number of hydrogen in most of its compounds

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Answer

The oxidation number of hydrogen in most of its compounds is +1 due to its higher electronegativity compared to most other elements. In hydrides, however, hydrogen is bonded to more electropositive elements, which results in it having an oxidation number of -1.

Step 4

Define reduction in terms of (iv) oxidation number of oxygen in OF₂

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Answer

In most compounds, the oxidation number of oxygen is -2. However, in the case of OF₂ (oxygen difluoride), the oxidation number of oxygen is +2 because fluorine, being more electronegative, takes the oxidation state of -1.

Step 5

Assign oxidation numbers and balance

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Answer

First, assign oxidation numbers:

Mn²⁺: +2
BiO₃⁻: +5 for Bi, -2 for each O (there are 3 O)
H⁺: +1
MnO₄⁻: +7 for Mn, -2 for each O (there are 4 O)
Bi³⁺: +3
H₂O: 0 (H: +1, O: -2)

Next, balance the half-reactions:

For the oxidation half-reaction:
For the reduction half-reaction:

Finally, combine and balance charges to get:

2 Mn²⁺ + 5 BiO₃⁻ + 14 H⁺ → 2 MnO₄⁻ + 5 Bi³⁺ + 7 H₂O

Step 6

Identify the reducing agent in (vi)

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Answer

The reducing agent in the reaction is Mn²⁺, as it donates electrons to reduce BiO₃⁻ and itself is oxidized to MnO₄⁻.

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Define reduction in terms of (i) electron transfer, (ii) change in oxidation number - Leaving Cert Chemistry - Question 11 - 2022

Worked Solution & Example Answer:Define reduction in terms of (i) electron transfer, (ii) change in oxidation number - Leaving Cert Chemistry - Question 11 - 2022

Define reduction in terms of (i) electron transfer

Define reduction in terms of (ii) change in oxidation number

Define reduction in terms of (iii) oxidation number of hydrogen in most of its compounds

Define reduction in terms of (iv) oxidation number of oxygen in OF₂

Assign oxidation numbers and balance

Identify the reducing agent in (vi)

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