# Oxidation and Reduction

22 March 2023
Chapter 10. Oxidation and Reduction
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Slide 1: Tekstslide
PhysicsSecondary EducationAge 12,13

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## Onderdelen in deze les

22 March 2023
Chapter 10. Oxidation and Reduction

#### Slide 1 -Tekstslide

Content objectives

• Define oxidation in terms of: (a) loss of electrons ; (b) an increase in oxidation number
• Define reduction in terms of: (a) gain of electrons ; (b) a decrease in oxidation number
• Identify redox reactions as reactions involving gain and loss of electrons
• Identify redox reactions by changes in oxidation number using: (a) the oxidation number of elements in their uncombined state is zero ; (b) the oxidation number of a monatomic ion is the same as the charge on the ion; (c) the sum of the oxidation numbers in a compound is zero; (d) the sum of the oxidation numbers in anion is equal to the charge on the ion

#### Slide 2 -Tekstslide

Define oxidation in terms of: (a) loss of electrons ; (b) an increase in oxidation number
Define reduction in terms of: (a) gain of electrons ; (b) a decrease in oxidation number
Oxidation
• loss of electrons
Reduction
• gain of electrons

#### Slide 3 -Tekstslide

Identify redox reactions as reactions involving the gain and loss of electrons
• zinc + copper sulfate → zinc sulfate + copper
• Zn     +  CuSO4               → ZnSO4            + Cu
• Zn(s) + Cu2+(aq) + SO42-(aq) →Zn2+(aq) + SO42-(aq) + Cu(s)
Remember:
• Spectator ions (those that do not change) are SO42-(aq). These can be removed, leaving behind the ionic equation.
• ionic equation:      Zn0(s) + Cu2+(aq) → Zn2+(aq) + Cu0(s)
What are the ionic half equations?

#### Slide 4 -Tekstslide

Identify redox reactions as reactions involving the gain and loss of electrons
• ionic equation:      Zn0(s) + Cu2+(aq) → Zn2+(aq) + Cu0(s)
What are the ionic half equations?

#### Slide 5 -Tekstslide

Oxidation
• loss of electrons
• oxidation number of element is increased
Ag → Ag+ + e-
Reduction
• gain of electrons
• oxidation number of element is decreased
O2 + 4e- → 2O2-
Redox reactions can be identified by the changes in the oxidation number when a reactant goes to a product.

#### Slide 6 -Tekstslide

Substance is oxidised when
• it has lost electrons
Ag → Ag+ + e-
Substance is reduced when
• it has gained electrons
O2 + 4e- → 2O2-

#### Slide 8 -Tekstslide

Practice
• The equation for the reaction between chlorine and potassium iodide is shown below.

Cl2 + 2KI → 2KCl + I2

Identify which species has been:

a) oxidised

b) reduced
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#### Slide 9 -Tekstslide

22 March 2023
Chapter 10. Oxidation and Reduction

#### Slide 10 -Tekstslide

Oxidising agent
• a substance that oxidises another substance and becomes reduced in the process
• gains electrons as another substance loses electrons
• Common examples include hydrogen peroxide, fluorine, and chlorine

#### Slide 11 -Tekstslide

Reducing agent
• a substance that reduces another substance, and becomes oxidised in the process
• loses electrons as another substance gains electrons
• Common examples include carbon and hydrogen

#### Slide 12 -Tekstslide

Identifying Redox Reactions by Colour Changes
• observation of a colour change in the solution being analysed
• acidified potassium manganate(VII), KMnO4 - oxidising agent which is often used to test for the presence of reducing agents
• potassium iodide, KI - a reducing agent which is often used to test for the presence of oxidising agents

Practice
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#### Slide 14 -Tekstslide

Test for reducing agents

#### Slide 15 -Tekstslide

Test for oxidising agents
When added to an acidified solution of an oxidising agent such as aqueous chlorine or hydrogen peroxide (H2O2), the solution turns a red-brown colour due to the formation of iodine, I2
solution
2KI (aq) + H2SO4 (aq) + H2O2 (aq) → I2 (aq) + K2SO4 (aq) + 2H20 (l)

#### Slide 16 -Tekstslide

STEPS
• Step 1 - Write half equations to work out what has gained/lost electrons
• Step 2 - Deduce what has been oxidised / reduced (remember OIL RIG)
• Step 3 - Identify the reducing agent

#### Slide 17 -Tekstslide

Try to apply the steps!
• When iron reacts with bromine to form iron(II) bromide, a redox reaction occurs:

Fe + Br2 → FeBr2

What is acting as the reducing agent in this reaction?
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Plenary

What's next?

#### Slide 20 -Tekstslide

Define redox reactions as involving simultaneous oxidation and reduction.
Define oxidation as the gain of oxygen and reduction as the loss of oxygen.
Oxidation
zinc oxide + carbon → zinc  + carbon monoxide
ZnO      +  C         →  Zn   +   CO
• gain of oxygen
Reduction
• loss of oxygen

#### Slide 21 -Tekstslide

Identify redox reactions as reactions involving gain and loss of oxygen
Identify oxidation and reduction in redox reactions

#### Slide 22 -Tekstslide

Identify redox reactions as reactions involving gain and loss of oxygen
Identify oxidation and reduction in redox reactions

#### Slide 23 -Tekstslide

Use a Roman numeral to indicate the oxidation number of an element in a compound
FeO       - Name: Iron (II) oxide
Fe2O3   - Name: Iron (III) oxide
CuCl2    - Name: Copper (II) chloride
CuCl    - Name: Copper (I) chloride

#### Slide 25 -Tekstslide

Define oxidation in terms of: (a) loss of electrons ; (b) an increase in oxidation number
Define reduction in terms of: (a) gain of electrons ; (b) a decrease in oxidation number
Oxidation Number
• (also called oxidation state) is a number assigned to an atom or ion in a compound that indicates the degree of oxidation (or reduction)
• shows the number of electrons that an atom has lost, gained, or shared in forming a compound
• helps you to keep track of the movement of electrons in a redox process
• written as a +/- sign followed by a number (not to be confused with charge, which is written by a number followed by a +/- sign)