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MED 102- GENERAL CHEMISTRY > OXIDATION AND REDUCTION REACTIONS > Flashcards

OXIDATION AND REDUCTION REACTIONS Flashcards

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1
Q
  1. What happens in this reaction where Sodium Magnesium Metal is placed in a solution of Hydrochloric Acid?
A
  • the magnesium dissolves in the acid
  • there are bubbles of the colourless hydrogen gas that
    are released
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2
Q
  1. Why is this an example of a Redox Reaction?
A
  • Magnesium loses electrons
  • it is oxidised
  • Mg (s) → Mg2+ (aq) + 2e-
  • the Hydrogen ions from the hydrochloric acid gain
    electrons
  • they become hydrogen gas
  • they gain electrons
  • this is known as reduction
  • 2H+ (aq) + 2e- →H2 (g)
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3
Q
  1. What are the rules of Assigning Oxidation Numbers?
A
  1. An atom in its elemental form has an oxidation
    number of 0
  2. An atom in a monatomic ion has an oxidation number
    equal to its charge
  3. An atom in a polyatomic ion or in a molecular
    compound has the same oxidation number as it
    would have if it were a monatomic ion
  4. The sum of oxidation numbers is 0 for neutral
    compounds
    . it is also equal to the total charge for a polyatomic ion
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4
Q
  1. What are the exceptions for the Oxidation Numbers
    Rules?
A
  • Hydrogen can either be +1 or -1
  • When Hydrogen is bonded to a metal:
    • it will have a -1 charge
  • When Hydrogen is bonded to a nonmetal:
    - it will have a +1 charge
  • Oxygen usually has a charge of -2
  • except in peroxides
  • which contain the O₂2- anion
  • this is where oxygen has a charge of -1
  • Halogens (Group 7 elements) are usually -1
  • except when bonded to Oxygen or Fluorine
  • these are highly electronegative elements
  • halogens have a positive oxidation number when
    bonded to these elements
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5
Q
  1. What are the Oxidation Numbers for CdS?
A
  • S is in Group 6
  • it has a 2- charge
  • Cd has a charge of 2+
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6
Q
  1. What are the Oxidation Numbers for AlH3?
A
  • H has a charge of 1-
  • 3 H’s have a charge of 3-
  • Al has a charge of 3+
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7
Q
  1. What are the Oxidation Numbers for (S2 O3)2-?
A
  • O has a charge of 2-
  • 3 O’s have a charge of 6-
  • the total charge of the polyatomic ion of 2-
  • the two S’s must add up to 4+
  • this means that one S has a charge of 2+
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8
Q
  1. What are the Oxidation Number for Na2 Cr2 O7?
A
  • Na has a charge of 1+
  • 2 Na’s have a charge of 2+
  • O has a charge of 2-
  • 7 O’s have a charge of 14-
  • Na2 Cr2 O7
  • should have an overall charge of 0
  • the two Cr’s must add up to 12+
  • each Cr has a charge of 6+
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9
Q
  1. What are the Oxidation Number for FeSO4?
A
  • SO4 has a charge of 2-
  • Fe needs to have a charge of 2+
  • O has a charge of 2-
  • 4 O’s have a charge of 8-
  • S must have a charge of 6+
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10
Q
  1. Learn these.
A
  • deal
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11
Q
  1. Which elements are oxidised and which are reduced
    in the following equation:

H2 (g) + ½ O2 (g) → H2O (l)

A
  • the oxidation number for Hydrogen goes from 0
  • to 1+
  • it loses an electron for each hydrogen atom
  • two electrons are last in total
  • the hydrogen is oxidised
  • the Oxygen goes from 0 to 2-
  • it is reduced
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12
Q
  1. What is a substance that causes reduction called?
A
  • a reducing agent
  • the reducing agent is oxidised
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13
Q
  1. What is a substance that causes oxidation called?
A
  • an oxidising agent
  • the oxidising agent is reduced
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14
Q
  1. In this equation, which is the oxidising and which is the reducing agent?

Mg + Cl2 → Mg2+ + 2Cl-

A
  • Mg loses 2 electrons
  • it is oxidised
  • Cl gains one electron
  • it is reduced
  • Cl2 is the oxidising agent
  • Mg is the reducing agent
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15
Q
  1. In this equation, which is the oxidising and which is the reducing agent?

Ca (s) + 2 H+ (aq) → Ca2+(aq) + H2 (g)

A
  • Ca loses 2 electrons
  • it is oxidised
  • H+ gains one electron
  • it is reduced
  • H+ is the oxidising agent
  • Ca is the reducing agent
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16
Q
  1. In this equation, which is the oxidising and which is the reducing agent?

2FE²⁺ (aq) + Cl2 (g) → 2 Fe3+(aq) + 2Cl-(aq)

A
  • Fe2+ loses 2 electrons
  • it is oxidised
  • Cl2 gains one electron
  • it is reduced
  • Cl2 is the oxidising agent
  • Fe2+ is the reducing agent
17
Q
  1. What is the result of a reaction with an aqueous cation with a free element?

AQUEOUS CATION = metal ion

A
  • it gives a different cation
  • it gives a different free element
    (this is an example of simple redox reaction)
18
Q
  1. What happens when an iron nail reacts with a copper sulphate solution?

Fe(s) + Cu2+(aq) → Fe2+ (aq) + Cu (s)

A
  • this is a spontaneous reaction
  • it can happen naturally
  • there is no added energy needed to complete the
    reaction
  • the Copper Sulphate solution will go from blue to
    green
  • this indicates an aqueous solution of Fe2+
  • the iron nail will form a layer of elemental copper on it
  • it is brown/orange in colour
19
Q
  1. Would this reaction be able to work in reverse:
    Fe(s) + Cu2+(aq) → Fe2+ (aq) + Cu (s)
A
  • no
  • unless there is an energy input
  • this reaction is not spontaneous
20
Q
  1. What does this image show?
A
  • the Activity Series
  • the most reactive elements are at the top of the
    table
  • they are the most easily oxidised
  • elements at the bottom of the table do not oxidise easily
  • they do not rust easily
21
Q

21.1. Does this reaction occur spontaneously?
Mg(s) + 2 H+(aq) → Mg2+(aq) + H2(g)

21.2. Would it be spontaneous if we replaced the
Magnesium with Gold?

A

21.1. yes
- the magnesium will dissolve in the acid
- this forms a solution
- this is because Mg is higher on the table than
hydrogen (H2)

21.2. no
- no reaction will take place
- this is because Gold is a very non reactive
metal
- it is lower than H2 on the Activity Series
- this means that it will not react with an acid

22
Q
  1. Will this reaction take place spontaneously as written?

Hg2+(aq) + Zn(s) → Hg(l) + Zn2+(aq)

A
  • yes
  • Hg2+ is being reduced
  • Zn is being oxidised
  • Zn is higher than Hg on the Activity Series
  • this means that it prefers to be in ionic form
  • this means that Hg prefers to be in Metallic form
  • this matches the written reaction
23
Q
  1. Will this reaction take place spontaneously as written?

Cu(s) + 2 H+(aq) → Cu2+(aq) + H2(g)

A
  • no
  • Cu is oxidised
  • H+ is reduced
  • Cu is below the H2 in the Activity Series
  • it prefers to stay in its metallic form
  • H2 prefers to be in ionic form
  • this does not match the written reacton
23
Q
  1. Will this reaction take place spontaneously as written?

Cu(s) + 2 H+(aq) → Cu2+(aq) + H2(g)

A
  • no
  • Cu is oxidised
  • H+ is reduced
  • Cu is below the H2 in the Activity Series
  • it prefers to stay in its metallic form
  • H2 prefers to be in ionic form
  • this does not match the written reacton
24
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes

MED 102- GENERAL CHEMISTRY (27 decks)

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