Topic 3: Redox Flashcards

1
Q

What does the oxidation number tell you?

A
  • oxidation numbers or oxidation state tell you 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 are the rules to assign oxidation numbers?

A

§ All uncombined elements have an oxidation number of 0

  • this means they haven’t accepted or donated any electrons
  • elements bonded to identical atoms will also have oxidation numbers of 0
  • eg. any uncombined element
  • O2 or H2

§ The oxidation number of a simple monatomic ion is the same as its charge

  • Na+ has an oxidation number of +1
  • Mg2+ has oxidation state of +2

§ For molecular ions, the sum of the oxidation numbers is the same as the overall charge of the ion

  • each of the constituent atoms will have an o.n of their own and the sum equals overall charge
    e. g. SO4 2- : -8 (for oxygen) +6 = -2

§ For a neutral compound, overall charge is 0

§ Hydrogen always has an oxidation number of +1, except in metal hydrides (MHx) where its -1 and in molecular hydrogen (H2) where it is 0

§ Oxygen nearly away has an oxidation number of -2, except in peroxides (O2 2-) where it is -1, and molecular oxygen where it is 0

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3
Q

What do Roman numerals show?

A
  • tells you the oxidation number
  • if an element can have multiple oxidation numbers, or it isn’t a normal oxidant number
  • the numerals are written after the name of the element they correspond to
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4
Q

Explain the roman numerals in ions that contain oxygen, so end with -ate

A
  • the other element in the -ate ion can exist in different oxidation numbers, so it is attached as a Roman numeral after the number of the -ate compound
  • correspond to the non-oxygen element
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5
Q

What is oxidation?

A
  • a loss of electrons
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6
Q

What is reduction?

A
  • a gain in electrons
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7
Q

What is a redox reaction?

A
  • reduction and oxidation happen simultaneously
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8
Q

What is an oxidising agent?

A
  • accept electrons

- gets reduced

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9
Q

What is a reducing agent?

A
  • donates electrons

- gets oxidised

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10
Q

What happened if the oxidation number has increased after there reaction?

A
  • element has lost electrons

- been oxidised

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11
Q

What happened if the oxidation number has decreased after the reaction?

A
  • element has gained electrons

- been reduced

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12
Q

Identify the reducing and oxidising agents in this reaction:

4Fe + 3O2 = 2FeO3

A
  • iron has gone from having an oxidation number of 0 to a number of 3+
  • lost electrons and has been oxidised
  • reducing agent
  • oxygen has gone from an oxidation number of 0 to an oxidation number of -2
  • gained electrons and reduced
  • oxidising agent
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13
Q

What is a disproportionation reaction?

A
  • a special redox reaction

- an element in a single species is simultaneously reduced and oxidised

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14
Q

What do ionic half equations show?

A
  • they show oxidation and reduction

- you can show electrons being lost or gained in a half equation

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15
Q

What does combining half equations for different oxidising and reducing agents do?

A
  • makes full equations for redox reactions
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16
Q

Why do you have to add some H+ ions and H2O to half equations sometimes?

A
  • you can’t balance the equation by just multiplying reactant and products