Oxidation + Reduction - Chp 14

Oxidation (old)

the addition of oxygen to a substance

Reduction (old)

the removal of oxygen from a substance

Oxidation (in terms of electron transfer)

of an element takes place when it loses electrons

Oxidation (in terms of oxidation number)

is an increase in oxidation number

Reduction (in terms of electron transfer)

of an element takes place when it gains electrons

Reduction (in terms of oxidation number)

is a decrease in oxidation number

Oxidising agent

is a substance that brings about oxidation in other substances

Reducing agent

is a substance that brings about reduction in other substances

What are examples of common oxidising agents?

- hydrogen peroxide, used to bleach hair

- tincture of iodine, iodine and ethanol solution in first aid kits

- chlorine, used to disinfect water

- sodium hypochlorite, present in household bleaching agents

What are examples of common reducing agents?

- carbon monoxide, removes oxygen from iron ore

- sulfur dioxide, used to bleach wood and textiles

Oxidation number

• is the charge that an atom has or appears to have

• when electrons are distributed according to certain rules

What are the rules for assigning oxidation numbers?

- atoms in a free element, ON = 0

- simple ions, ON = charge on ion

- compound, ON = 0

- oxygen, ON = -2, peroxide ON = -1, OF₂ ON = +2

- hydrogen, ON = +1, metal hydride ON = -1

- halogen ON = -1, unless bonded to more electronegative element

- group 1, ON = +1, unless existing as a free element

- group 2, ON = +2, unless existing as a free element

- complex ion, ON = overall charge

What is the most powerful reducing agent?

Fluorine, it is the most electronegative element

Colour of chlorine water

pale yellow-green

Colour of bromine water

yellow-orange

Colour of iodine water

red-brown

Write an equation for the reaction that occurs when chlorine water is bubbled through a solution containing bromide salts:

Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

Reduction: Cl₂ + 2e⁻ → 2Cl⁻

Oxidation: 2Br⁻ ₋ 2e⁻ → Br

Appearance of yellow orange colour

Write an equation for the reaction that occurs when chlorine water is bubbled through a solution containing iodide salts:

Cl₂ + 2I⁻ → 2Cl⁻ + I₂

Reduction: Cl₂ + 2e⁻ → 2Cl⁻

Oxidation: 2I⁻ ₋ 2e⁻ → I₂

Appearance of red-brown colour

Write an equation for the reaction that occurs when bromine water is bubbled through a solution containing iodide salts:

Br₂ + 2I⁻ → 2Br⁻ + I₂

Reduction: Br₂ + 2e⁻ → 2Br⁻

Oxidation: 2I⁻ ₋ 2e⁻ → I₂

Appearance of red-brown colour

Write an equation for the redox reaction between chlorine and solution containing sulfite ions:

Cl₂ + SO₃²⁻ + H₂O → 2Cl⁻ + SO₄²⁻ + 2H⁺

Reduction: Cl₂ + 2e⁻ → 2Cl⁻

Oxidation: SO₃²⁻ + H₂O ₋ 2e⁻ → SO₄²⁻ + 2H⁺

No change in appearance until barium chloride is added

Write an equation for the redox reaction between chlorine and iron (III) ions

Cl₂ + 2Fe²⁺ → 2Cl⁻ + 2Fe³⁺

Reduction: Cl₂ + 2e⁻ → 2Cl⁻

Oxidation: 2Fe²⁺ ₋ 2e⁻ → 2Fe³⁺

A greenish-brown precipitate forms

What is observed in the displacement reaction between powdered zinc in copper sulfate solution?

appearance of red-brown copper metal

CuSO₄ solution loses some or all of its blue colour

Oxidation: Zn - 2e⁻ → Zn²⁺

Reduction: Cu²⁺ + 2e⁻ → Cu

What is observed in the displacement reaction between a magnesium ribbon in copper sulfate solution?

magnesium metal becomes coated with a red-brown metal, the blue solution begins to lose its blue colour

Oxidation: Mg - 2e⁻ → Mg²⁺

Reduction: Cu²⁺ + 2e⁻ → Cu