Topic 3 - Redox I Flashcards

1
Q

What does an atom’s oxidation number tell you?

A

How many electrons an atom has donated or accepted to form an ion or form part of a compound.

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2
Q

What is an atom’s oxidation number the same as?

A

Its charge.

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3
Q

How does an atom’s oxidation number relate to a molecular ion’s overall charge?

A

The charge is equal to the sum of the oxidation numbers.

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4
Q

Describe the oxidation number of hydrogen.

A
  • Usually -> +1
  • In metal hydrides -> -1
  • In molecular hydrogen -> 0
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5
Q

Describe the oxidation number of oxygen.

A
  • Usually -> -2
  • In peroxides (O₂²⁻) -> -1
  • In molecular oxygen -> 0
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6
Q

How can the oxidation number of an atom or group be indicated in a formula?

A

Using Roman numerals.

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7
Q

How does the position of a Roman numeral in a formula relate to the oxidation numbers of the atoms or groups?

A

The Roman numeral is always after the thing it describes.

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8
Q

What is oxidation?

A

A loss of electrons.

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9
Q

What is oxidation?

A

Loss of electrons

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10
Q

What is reduction?

A

Gain of electrons

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11
Q

What is a redox reaction?

A

Where oxidation and reduction happen simultaneously.

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12
Q

What happens to the oxidation number when an electron is lost?

A

Increases by 1

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13
Q

What happens to the oxidation number when an electron is gained?

A

Decreases by 1

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14
Q

How can you work out if something has been oxidised or reduced?

A
  • Assign oxidation numbers to the element before and after the reaction
  • If the oxidation number increases -> This is oxidation
  • If the oxidation number decreases -> This is reduction
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15
Q

What is a disproportionation reaction?

A

When a single species is simultaneously oxidised and reduced.

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16
Q

What types of equation show oxidation or reduction?

A

Half-equations

17
Q

Describe the process of writing a full equation using half-equations of reduction and oxidation.

A

1) Write down the half-equations
Look at each equation and:
2) Balance the oxygens using water on the right
3) Balance the hydrogens by adding H⁺’s on the left
4) Balance the charges using electrons
5) Make sure the electrons in each half-equation are the same
6) Now, combine the two half-equations

(See example pg 41 of revision guide)

18
Q

When balancing redox reaction, what 3 things can be used?

A
  • H⁺
  • H₂O
  • e⁻
19
Q

Acidified manganate(VII) ions (MnO₄⁻) can be reduced to Mn²⁺ by Fe²⁺ ions. Write the full equation for this reaction.

A
For manganate:
• MnO₄⁻ -> Mn²⁺
• MnO₄⁻ -> Mn²⁺ + 4H₂O
• MnO₄⁻ + 8H⁺ -> Mn²⁺ + 4H₂O
• MnO₄⁻ + 8H⁺ + 5e⁻ -> Mn²⁺ + 4H₂O
For iron:
• Fe²⁺ -> Fe³⁺ + e⁻
• 5Fe²⁺ -> 5Fe³⁺ + 5e⁻
Overall:
• MnO₄⁻ + 8H⁺ + 5Fe²⁺ -> Mn²⁺ + 5Fe³⁺ + 4H₂O