6.1 Electrochemistry: Redox Processes

6.1 Electrochemistry: Redox Processes

6.1 Electrochemistry: Redox Processes

​Page 21 of the CIE 0654 Syllabus

6.1 Electrochemistry: Oxidation numbers

​1. All elements have an oxidation number of 0

​Transition metals can have a range of oxidation states, but in their elemental state it's always equal to zero

6.1 Electrochemistry: Oxidation numbers

​2. The oxidation states of the atoms in a molecule add up to 0

​Note: The syntax of charges. 

• ​When using a symbol we quote the number-sign, e.g. Al³⁺

• If you are referring to the oxidation number then we use sign-number​,

  e.g. Aluminium has a charge of +3. 

6.1 Electrochemistry: Oxidation numbers

3. The oxidation state of an ion is the same as it’s charge

​Transition metals can have a range of oxidation states. The oxidation number of each charged species is equal to the charge on the ion.

​Cr³⁺ = +3

Multiple Choice

What is the oxidation state of H in H₂?

• 0

• +1

• -1

• -2

Multiple Choice

What is the oxidation state of C in CO₂?

• -4

• -2

• +2

• +4

Multiple Choice

What is the oxidation of C in CH₄?

• -4

• -1

• +1

• +4

6.1 Electrochemistry: Oxidation numbers

4. 1-2-3-F-H-O-C

​Note: Group 3 = +3 (always for A-level Chemistry)

6.1 Electrochemistry: Oxidation numbers

5. The sum of the oxidation states is equal to the overall charge on the particle

• ​Pick out the oxidation numbers that are standard, O = -2 unless bonded to F.

• ​Sulfur has variable oxidation states, we must use the overall charge to calculate S.

• ​We have 4 x Oxygen = 4 x -2 = -8 + unknown S = -2

• ​-2 + 8 = +6

6.1 Electrochemistry: Oxidation numbers

5. The sum of the oxidation states is equal to the overall charge on the particle

Multiple Choice

What is the oxidation number of Fe in FeO?

• +1
• -1
• +2
• -2

Multiple Choice

What is the oxidation number of O in CO₂?

• +2
• -1
• +4
• -2

Multiple Choice

What is the oxidation number of N in NO₂^1- ?

• -3
• +4
• -2
• +3

Multiple Choice

The sum of all oxidation numbers in a neutral compound is ___.

• 0
• 1
• -1
• depends on the compound

Multiple Choice

What is the oxidation of C in CH₄?

• -4
• -1
• +4
• +1

Multiple Choice

What is oxidation number of Mn in MnO₂ ?

• 0
• +2
• -2
• +4

Multiple Choice

What is the oxidation number of Ca in Ca₃N₂?

• +3
• +2
• -3
• -2

Multiple Choice

What is oxidation number of Cr in
Cr₂O₇^2-?

• -2
• +2
• +6
• +12

6.1 Electrochemistry: Oxidation numbers

​6.1.3 explain and use the terms redox, oxidation, reduction and disproportionation. e.g. Reactions of Chlorine with NaOH

​

6.1 Electrochemistry: Oxidation numbers

​6.1.3 explain and use the terms redox, oxidation, reduction and disproportionation. e.g. Reactions of Chlorine with NaOH

​

​2 NaOH + Cl2 à NaCl + NaClO + H2O

• ​The reaction of COLD and DILUTED NaOH with Chlorine

• ​Assign oxidation numbers for each element

Multiple Choice

What is the correct name of NaClO?

• sodium chlorate
• sodium chlorite
• sodium perchlorate
• sodium hypochlorite

Multiple Choice

Cl₂ + 2OH^- Cl^- + ClO^- + H₂O

Chlorine has been

• Oxidised

• Reduced

• Both

• Neither

​Oxidising & Reducing Agents

• ​Reducing agent - this causes another species to be reduced, hence itself is oxidised.

​

• ​Oxidising agent - will oxidise another chemical species but itself is reduced.

HOMEWORK because people were complaining they don't get enough in chemistry. 

Multiple Choice

Which of the following are the example of oxidation?

• P → PH₃

• O₂ → H₂O

• CH₄ → CO₂

• MnO₄²⁻ → MnO₂

Multiple Choice

Which of the following statement(s) is/are held true for oxidation and reduction?

1.Reaction :

CaCO₃ → CaO + CO₂

is not a redox reaction

2.Oxidation number of Li in any compound is +1

3.The lower the oxidation number of atom making up the compound, the higher the tendency for the compound to undergo oxidation

• 1, 2, and 3

• 1 and 2

• 2 and 3

• 1 and 3

Multiple Choice

In which substance does nitrogen exhibit the highest oxidation state?

• NO

• N₂O

• N₂O₄

• NaNO₂

Multiple Choice

Given the following reaction :

VO₂⁺ + SO₂ → V³⁺ + SO₄²⁻

Which one is a oxidising agent

• VO₂⁺

• SO₂

• V³⁺

• SO₄²⁻

Multiple Choice

Sulfur dioxide, SO₂, reacts with bromine, Br₂, according to the following equation :

a SO₂ + b Br₂ + c H₂O → d SO₄²⁻ + e Br⁻ + f H⁺

what will be the values of a and e in a balanced chemical reaction, respectively?

• 2, 1

• 1, 2

• 2, 3

• 1, 3

Multiple Choice

In the industrial process of nitric acid, the picture shows how nitrogen change in sequence of steps to yield nitric acid.

In which step is the nitrogen reduced?

• step 4

• step 2

• step 1

• step 3

Multiple Choice

Solid potassium halide react with concentrated sulfuric acid according to the following equation :

2KBr + 2H₂SO₄ → K₂SO₄ + SO₂ + Br₂ + 2H₂O

What is the change in oxidation number of sulfur in this reaction?

• 0 to +4

• +4 to +3

• +2 to +4

• +6 to +4

Multiple Choice

Which of the following reactions is a redox reaction?

• Al(OH)₃ + 3HCl → AlCl₃ + 3H₂O

• 2KClO₃ → 2KCl + 3O₂

• Na₂S + HCl → 2NaCl+ H₂S

• H₂O → H⁺ + OH^-

Multiple Choice

What is the oxidation number of 2 nitrogen atoms in N₂O₅ ?

• +10

• +15

• +5

• 0

Multiple Choice

What is the oxidation number of chromium in sodium chromate, K₂CrO₄ ?

• +6

• +5

• +4

• +3