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HKDSE Chemistry > 20: Oxidation and Reduction > Flashcards

20: Oxidation and Reduction Flashcards

1
Q

What is the definition of oxidation in terms of gain and loss of oxygen?

A

Oxidation is the gain of oxygen by a chemical species.

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2
Q

What is the definition of reduction in terms of gain and loss of oxygen?

A

Reduction is the loss of oxygen by a chemical species.

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3
Q

What is a redox reaction?

A

A redox reaction is a reaction in which reduction and oxidation take place.

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4
Q

What is an oxidising agent?

A

An oxidising agent oxidises another chemical species, and is reduced itself in the process.

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5
Q

What is a reducing agent?

A

A reducing agent reduces another chemical species, and is oxidised itself in the process.

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6
Q

What is the definition of oxidation in terms of gain and loss of hydrogen?

A

Oxidation is the loss of hydrogen by a chemical species.

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7
Q

What is the definition of reduction in terms of gain and loss of hydrogen?

A

Reduction is the gain of hydrogen by a chemical species.

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8
Q

What is the definition of oxidation in terms of gain and loss of electrons?

A

Oxidation is the loss of electrons by a chemical species.

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9
Q

What is the definition of reduction in terms of gain and loss of electrons?

A

Reduction is the gain of electrons by a chemical species.

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10
Q

What are the properties of a metal high in the electrochemical series?

A

It is a strong reducing agent and its ion is a weak oxidising agent.

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11
Q

What are the properties of a metal low in the electrochemical series?

A

It is a weak reducing agent and its ion is a strong oxidising agent.

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12
Q

List 2 differences between the electrochemical series and the metal reactivity series.

A
  1. Calcium is above sodium in the electrochemical series while it is below sodium in the reactivity series.
  2. There is hydrogen included between lead and copper in the electrochemical series but not the reactivity series.
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13
Q

What is the oxidation number of group I metals?

A

+1

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14
Q

What is the oxidation number of group II metals?

A

+2

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15
Q

What is the oxidation number of fluorine in a compound?

A

-1

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16
Q

What is the oxidation number of hydrogen in a covalent compound?

A

+1

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17
Q

What is the oxidation number of hydrogen in an ionic compound?

A

-1

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18
Q

What is the oxidation number of oxygen in a compound usually?

A

-2

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19
Q

What is the oxidation number of oxygen in hydrogen peroxide?

A

-1

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20
Q

What is the oxidation number of oxygen in oxygen difluoride?

A

+2

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21
Q

What is the sum of oxidation numbers in a neutral compound?

A

0

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22
Q

What is the sum of oxidation numbers in an ion with charge 2+?

A

+2

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23
Q

What is the sum of oxidation numbers in an element?

A

0

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24
Q

What is the definition of oxidation in terms of change in oxidation number?

A

Oxidation occurs when the oxidation number of an element in a chemical species increases.

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25
What is the definition of reduction in terms of change in oxidation number?
Reduction occurs when the oxidation number of an element in a chemical species **decreases**.
26
Identify and explain the oxidising agent and the reducing agent in the reaction: Cu + 2AgNO3 -> 2Ag + Cu(NO3)2
Cu **is oxidised** since its oxidation number **increases** from 0 in Cu to +2 in Cu(NO3)2. Hence it is the**reducing agent**. Ag in AgNO3 **is reduced** since its oxidation number **decreases** from +1 in AgNO3 to 0 in Ag. Hence AgNO3 is the **oxidising agent**.
27
What is the Stock system name and chemical formula of chromate ion?
Chromate(VI) ion, CrO42-
28
What is the Stock system name and chemical formula of dichromate ion?
Dichromate(VI) ion, Cr2O72-
29
What is the Stock system name and chemical formula of permanganate ion?
Manganate(VII) ion, MnO4-
30
What is the Stock system name and common name of MnO42-?
Manganate(VI) ion, Manganate ion
31
What is the Stock system name and chemical formula of hypochlorite ion?
Chloride(I) ion, OCl-
32
What is the Stock system name and chemical formula of chlorate ion?
Chloride(V) ion, ClO3-
33
What is the Stock system name and chemical formula of sulphite ion?
Sulphate(IV) ion, SO32-
34
What is the Stock system name and chemical formula of sulphate ion?
Sulphate(VI) ion, SO42-
35
List 7 common oxidising agents.
Acidified potassium permanganate solution, acidified potassium dichromate solution, iron(III) ions, chlorine water, dilute nitric acid, concentrated nitric acid, hot and concentrated sulphuric acid
36
List 5 common oxidising agents which have a colour change within their reaction.
1. Acidified potassium permanganate solution: purple permanganate ions to colourless / pale pink manganese ions 2. Acidified potassium dichromate solution: orange dichromate ions to green chromium(III) ions 3. Iron(III) ions: yellow-brown iron(III) ions to pale green iron(II) ions 4. Chlorine water: very pale green to colourless chloride ions 5. Concentrated nitric acid: colourless to brown nitrogen dioxide gas
37
List a common oxidising agent which has a colour change after its reaction.
Dilute nitric acid: It produced colourless **nitrogen monoxide** gas, which then cones into contact with air to form **brown nitrogen dioxide gas**.
38
What is the ionic equation of the reduction of acidified potassium permanganate solution?
MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O
39
What is the ionic equation of the reduction of acidified potassium dichromate solution?
Cr2O72- + 14H+ + 6e- -> 2Cr3+ + 7H2O
40
What is the ionic equation of the reduction of iron(III) ions?
Fe3+ + e- -> Fe2+
41
What is the ionic equation of the reduction of chlorine water?
Cl2 + 2e- -> 2Cl-
42
What is the ionic equation of the reduction of dilute nitric acid?
NO3- + 4H+ + 3e- -> NO + 2H2O
43
What is the ionic equation of the reduction of concentrated nitric acid?
NO3- + 2H+ + e- -> NO2 + H2O
44
What is the ionic equation of the reduction of concentrated sulphuric acid?
H2SO4 + 2H+ + 2e- -> SO2 + 2H2O
45
List 4 common reducing agents.
Sulphite ion, iodide ion, iron(II) ion, zinc (or other reactive metal)
46
What is the ionic equation of the oxidation of sulphite ion?
SO32- + H2O -> SO42- + 2H+ + 2e-
47
What is the ionic equation of the oxidation of iodide ion?
2I- -> I2 + 2e-
48
What is the ionic equation of the oxidation of iron(II) ion?
Fe2+ -> Fe3+ + e-
49
What is the ionic equation of the oxidation of zinc?
Zn -> Zn2+ + 2e-
50
How should we balance ionic half equations in redox reactions?
1. Write the reactant and product. 2. Balance the number of oxygen atoms by adding water molecules. 3. Balance the number of hydrogen atoms by adding hydrogen ions. 4. Balance the total charge on both sides by adding electrons. 5. Check if all matter and charge is balanced.
51
How should we balance overall redox equations from ionic half reactions?
1. Write the reactants and products. 2. Calculate the change in oxidation number for both the reduction and oxidation reaction. 3. Balance the change in oxidation number so that the increase in the oxidation reaction is equal to the decrease in the reduction reaction. 4. Balance the total charge by adding hydrogen ions. 5. Balance the number of oxygen and hydrogen atoms by adding water molecules. 6. Check if all matter and charge is balanced.
52
What is the condition for redox reactions to be possible?
The oxidising agent reacts with the reduced form of any chemical species **above** them in the electrochemical series.
53
What is the colour of iodine in water?
Brown
54
How can we identify bromine water and iodine water?
Add **organic solvent** to each of the solutions. Bromine will have an **orange** colour in organic solvent while iodine will have an **purple** colour in organic solvent.
55
What are the products when chlorine reacts with cold sodium hydroxide solution?
Sodium chloride, sodium hypochlorite, and water.
56
What is the chemical equation when chlorine reacts with cold sodium hydroxide solution?
Cl2 + 2NaOH -> NaOCl + NaCl + H2O
57
What are the products when chlorine reacts with hot sodium hydroxide solution?
Sodium chloride, sodium chlorate, and water.
58
What is the chemical equation when chlorine reacts with hot sodium hydroxide solution?
Cl2 + 6NaOH -> 5NaClO3 + NaCl + 3H2O
59
What is a disproportionation reaction?
A reaction in which one element has been **both oxidised and reduced**, so its oxidation number **increase and decrease** at the same time.
60
What is the strength of hydrogen halide reducing agents HI, HBr, and HCl?
HI > HBr > HCl
61
What are the products when sodium halides react with concentrated sulphuric acid?
Hydrogen halide and sodium hydrogensulphate
62
What are the products when sodium chloride reacts with concentrated sulphuric acid?
Hydrogen chloride and sodium hydrogensulphate
63
What is the chemical equation when sodium chloride reacts with concentrated sulphuric acid?
NaCl + H2SO4 -> NaHSO4 + HCl
64
What are the products when sodium bromide reacts with concentrated sulphuric acid?
Hydrogen bromide and sodium hydrogensulphate are first produced. Then, hydrogen bromide is strong enough to **reduce** the concentrated sulphuric acid to **sulphur dioxide**; at the same time, **bromine liquid** and **water** are produced.
65
What are the chemical equations when sodium bromide reacts with concentrated sulphuric acid?
NaBr + H2SO4 -> NaHSO4 + HBr 2HBr + H2SO4 -> SO2 + Br2 + 2H2O
66
What are the products when sodium iodide reacts with concentrated sulphuric acid?
Hydrogen iodide and sodium hydrogensulphate are first produced. Then, hydrogen iodide is strong enough to **reduce** the concentrated sulphuric acid to **sulphur dioxide**; at the same time, **iodine solid** and **water** are produced. Hydrogen iodide can **further reduce** the sulphur dioxide into **sulphur** and then **hydrogen sulphide**. In the end, **hydrogen sulphide gas**, **iodine solid**, and water are produced.
67
What are the chemical equations when sodium iodide reacts with concentrated sulphuric acid?
NaI + H2SO4 -> NaHSO4 + HI 2HI + H2SO4 -> SO2 + I2 + 2H2O 6HI + H2SO4 -> 3I2 + S + 4H2O 8HI + H2SO4 -> H2S + 4I2 + 4H2O
68
What is the chemical equation when sulphur dioxide dissolves in water?
SO2 + H2O <-> H2SO3
69
Why is sulphur dioxide a good reducing agent?
When dissolved in water, it forms **sulphurous acid**, which release **sulphite ions** that can be oxidised to **sulphate ions** as its oxidation number increases from +4 to +6.
70
Name 4 solutions which can be reduced by aqueous sulphur dioxide.
Acidified potassium permanganate solution, acidified potassium dichromate solution, iron(III) sulphate solution, aqueous bromine.

HKDSE Chemistry (39 decks)

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