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Pure Chemistry > Chapter 12 - Oxidation and Reduction > Flashcards

Chapter 12 - Oxidation and Reduction Flashcards

1
Q

What is a redox reaction?

A

A redox reaction is a chemical reaction which involves oxidation and reduction simultaneously

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2
Q

What are the 4 ways to define oxidation?

A

Oxidation is the
- gaining of oxygen
- loss of hydrogen
- loss of electrons
- increase in oxidation state

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3
Q

What are 4 ways to define reduction?

A

Reduction is the
- loss of oxygen
- gaining of hydrogen
- gaining of electrons
- decrease in oxidation state

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4
Q

Why does rusting happen?

A

Iron undergoes a process called oxidation. Under the right conditions, iron will react with oxygen. As more oxygen reacts with iron, the iron gets converted from silvery iron metal to black and then red-brown iron compounds

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5
Q

State the rusting of iron balanced equation

A

When iron rusts, it reacts with oxygen to give hydrated iron (III) oxide shown by this equation:
4Fe + 3O2 + 2xH2O –> 2Fe2O3.xH2O

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6
Q

How is rusting reversed?

A

Iron is found in a mineral (haematite), which is mostly iron (III) oxide, Fe2O3. It can be extracted as a blast furnace by reacting with carbon monoxide. This causes iron (III) oxide to be reduced back to iron, losing all its oxygen

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7
Q

State the balanced equation of reverse of rusting

A

Fe2O3 + 3CO –> 2Fe + 3CO2
In this reaction, iron (III) oxide loses oxygen to become iron, but carbon monoxide gains oxygen to become carbon dioxide. So oxidation and reduction takes place at the same time

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8
Q

In, S + O2 –> SO2, which one is oxidised?

A

S gains oxygen, so S is oxidised

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9
Q

In, 2CuO + C –> 2Cu + CO2, which one is reduced?

A

CuO loses oxygen, so CuO is reduced

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10
Q

When deducing whether something has been oxidised or reduced, we look at the ____

A

Reactants

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11
Q

What is the equation for burning of methane and which is oxidised?

A

CH4 (g) + 2O2 (g) –> CO2 (g) + 2H2O (g)
Methane gains oxygen and is hence oxidised. However, it also loses hydrogen - by the time it becomes carbon dioxide, the carbon atom not only gained 2 oxygen atoms, but lost 4 hydrogen atoms

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12
Q

What is the overall equation for burning of hydrogen?

A

2H2 (g) + O2 (g) –> 2H2O (g)
Hydrogen gains oxygen and is oxidised to water vapour, oxygen gains hydrogen and is reduced to water vapour

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13
Q

In, 2HBr + Cl2 –> 2HCl + Br2, which one is oxidised?

A

HBr loses hydrogen, hence it is oxidised

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14
Q

In, 2HBr + Cl2 –> 2HCl + Br2, which one is reduced?

A

Cl2 gains hydrogen, hence it is reduced

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15
Q

When iron oxidises in the presence of oxygen and water to become rust, the iron atoms eventually become ____

A

Iron (III) ions/Fe^3+. The charge numbers on iron get larger as the iron atoms lose electrons and become ions

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16
Q

State the balanced chemical equation of iron atom losing electrons during rusting

A

Fe –> Fe^3+ + 3e-
Every iron atom in the reaction loses 3 electrons

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17
Q

If iron reacts with oxygen directly it will change from iron to ____

A

Iron (III) oxide. As iron oxidises, the oxygen gas becomes oxide ions

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18
Q

State the balanced chemical equation for rusting when iron loses electrons

A

O2 + 4e- –> 2O^2-
While iron loses electrons, the oxygen that reacts with it gains electrons

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19
Q

Which type of bonding does not involve oxygen, hydrogen or electron transfer?

A

Covalent bonding. This is why there is a more general definition of oxidation and reduction: oxidation state

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20
Q

What is the oxidation state?

A

The charge of an atom of an element would have if it is existed as an ion in a compound

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21
Q

Oxidation state can take on any positive or negative whole number or zero. True or false?

A

True

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22
Q

An increase in oxidation state (more +, less -) refers to the ____ of electrons and hence ____

A

Loss, oxidation

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23
Q

An decrease in oxidation state (more -, less +) refers to the ____ of electrons and hence ____

A

Gaining, reduction

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24
Q

For a compound with no net charge, what should all oxidation states add up to?

A

Zero

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25
Q

For an ion with a net charge, what should all oxidation states add up to?

A

The ion’s net charge

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26
Q

What oxidation state do you assign for atoms of the same elements (e.g. single atoms, molecules of any element, metallic elements)?

A

Zero (atoms of the same elements have no net charge)

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27
Q

What is the oxidation state of Na?

A

Zero (atoms of the same elements have no net charge)

28
Q

What is the oxidation state of H2?

A

Zero (atoms of the same elements have no net charge)

29
Q

What is the oxidation state of S8?

A

Zero (atoms of the same elements have no net charge)

30
Q

What oxidation state do you assign to group 1 metals in a compound?

A

+1 (Group 1 atoms will lose an electron)

31
Q

What is the oxidation state of Na in NaCl?

A

+1 (Group 1 atoms will lose an electron)

32
Q

What is the oxidation state of K in KCl?

A

+1 (Group 1 atoms will lose an electron)

33
Q

What is the oxidation state of Li in LiBr?

A

+1 (Group 1 atoms will lose an electron)

34
Q

What oxidation state do you assign to group 2 metals in a compound?

A

+2 (Group 2 atoms will lose 2 electrons)

35
Q

What is the oxidation state of Mg in MgCl2?

A

+2 (Group 2 atoms will lose 2 electrons)

36
Q

What is the oxidation state of Ca in CaCO3?

A

+2 (Group 2 atoms will lose 2 electrons)

37
Q

What oxidation state do you assign to aluminium in a compound?

38
Q

What is the oxidation state of aluminium in Al2O3?

39
Q

What is the oxidation state of aluminium in AlCl3?

40
Q

What oxidation state do you assign to group 17 non-metals in a compound? (e.g. Fluorine)

A

-1. Fluorine is the most reactive non metal and attracts electrons to itself strongly. Its oxidation state is always -1 (F-)

41
Q

What is the oxidation state of Cl2 in MgCl2?

42
Q

What is the oxidation state of Br in NaBr?

43
Q

What oxidation state do you assign to hydrogen in a compound usually (except metal hydride)?

A

+1. Hydrogen is a non-metal, but it usually has an oxidation state of +1. When it forms compounds with metals, it will have an oxidation state of -1

44
Q

What is the oxidation state of H2 in H2O?

45
Q

What is the oxidation state of H in HCl?

46
Q

What oxidation state do you assign to oxygen in a compound usually?

A

-2. Oxygen, is the next most likely to gain electrons. In peroxides the oxidation state is -1

47
Q

How do you assign oxidation states to elements form group 13 to 17 in compounds?

A

The oxidation states are often based on their most common valency

48
Q

What is the oxidation state of B in B2O3?

A

+3. Boron is a group 13 element, so it loses 3 electrons

49
Q

What is the oxidation state of C in CO2?

A

+4. Carbon is a group 14 element so it loses 4 electrons

50
Q

What is the oxidation state of C in CH4?

A

-4. Carbon is a group 14 element so it gain 4 electrons

51
Q

What is the oxidation state of N in NH3?

A

-3. Nitrogen is a group 15 element, so it gains 3 electrons

52
Q

What is the oxidation state of N in HNO3?

A

+5. Nitrogen is a group 15 element and in some cases, they can also share electrons and form +5 oxidation states

53
Q

What is the oxidation state of O in H2O?

A

-2. Oxygen is a group 16 element, so it gains 2 electrons

54
Q

What is the oxidation state of Cl in NaCl?

A

-1. Chlorine is a group 17 element, so it gains 1 electron

55
Q

What kind of oxidation state do you assign to metallic elements usually?

A

Almost always positive because metals tend to lose electrons

56
Q

What kind of oxidation state do you assign to non metals and metalloids

A

May be positive or negative

57
Q

What kind of oxidation state do you assign to elements from group 3 - 12, lanthanoids (57-71) and actinoids (89-103) in their compounds

A

Always positive. Elements in group 3 - 12 can have different oxidation states in their compounds. Roman numerals indicate the oxidation state (e.g. chromium (III) = +3)

58
Q

What are some reactions that are redox reactions?

A
  • Photosynthesis
  • Respiration
  • The Haber process
59
Q

What are some reactions that are not redox reactions?

A
  • Neutralisation (Acid + Base)
  • Precipitation of salt
60
Q

What is the definition of an oxidising agent?

A

A substance that causes the other substance to undergo oxidation while itself is reduced

61
Q

What is the definition of a reducing agent?

A

A substance that causes the other substance to undergo reduction while itself becomes oxidised

62
Q

If you are oxidised you are ____ agent

A

Reducing (e.g. hydrogen, reactive metals, carbon, potassium iodide)

63
Q

If you ae reduced you are ____ agent

A

Oxidising (e.g. oxygen, chloride, potassium manganate (VII))

64
Q

What is the test to test for presence of oxidising agent and what would be the result?

A

Acidified potassium manganate (VII) (KMnO4). Purple to colourless if O.A is present

65
Q

What is the test to test for presence of reducing agent and what would be the result?

A

Aqueous potassium iodide (KI). Colourless to yellow-brown

Pure Chemistry (11 decks)

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