REDOX-REACTIONS

REDOX-REACTIONS

Define the term oxidation in terms of electrons

This is the loss of electrons by an element in its free state or an element in a compound

Define the term reduction in terms of electrons

This is the gaining of electrons by an element in its free state or an element in a compound

What is an oxidation number?

This is a number given to an atom or ion in a chemical substance.

What is the purpose of an oxidation number?

It indicates the number of electrons being shared, loss, or gained as a result of a chemical bonding. 

What are the rules for determining oxidation numbers?

1. The oxidation number of each atom or ion of an element in its free uncombined state is zero (0).

2. The oxidation number of each monoatomic ion in an ionic compound is the same as the charge on the ion.

3. The oxidation number of hydrogen in a compound or polyatomic ion is always +1 except in metal hydrides where it is -1.

4. The oxidation number of oxygen in a compound or polyatomic ion is always -2 except in peroxides where it is -1.

5. Except for oxygen and hydrogen, the oxidation number of elements in covalent compounds and polyatomic ions may vary. The oxidation number may appear in the name of the compound or ion.

6. The sum of the oxidation numbers of all atoms or ions in a compound is zero.

7. The sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion.

Define the term oxidation in terms of oxidation numbers

This is the increase of oxidation number in an element in its free state or an element in a compound

Define the term reduction in terms of oxidation numbers

This is the decrease of oxidation number by an element in its free state or an element in a compound.

What is an oxidizing agent?

This is a reactant that causes another reactant to be oxidized.

What is a reducing agent?

This is a reactant that causes another reactant to be reduced.

In terms of electrons, what is the purpose of an oxidizing agent?

This causes an element to lose electrons 

In terms of electrons, what is the purpose of a reducing agent?

This causes an element to gain electrons

In terms of oxidation numbers, what is the purpose of an oxidizing agent?

This causes the oxidation number of an element to increase

In terms of oxidation numbers, what is the purpose of a reducing agent?

This causes the oxidation number of an element to decrease

What are visible changes that may occur when some oxidizing and reducing agents react?

A colour change

A precipitate may form

A particular gas may be produced

What are some common oxidizing agents?

1. Acidified potassium manganate (VII) solution (H⁺/KMnO₄)

2. Acidified potassium dichromate (VI) solution (H⁺/ K₂Cr₂O₇)

3. Aqueous iron (III) salts (Fe⁺³ (aq))

4. Sodium chlorate (I) solution (NaClO)

5. Hot concentrated sulphuric acid (H₂SO₄ (L))

6. Dilute or concentrated nitric acid (HNO₃(aq))

What visible colour change occurs when acidified potassium manganate react and what’s the reason?

Colour change: Purple to colourless 

Reason: The purple MnO₄^- ion forms the colourless Mn²⁺ ion. 

What visible colour change occurs when Acidified potassium dichromate (VI) solution (H⁺/ K₂Cr₂O₇) reacts and what’s the reason?

Colour change: Orange to green 

Reason: The orange Cr₂O₇^-2 ion forms the green Cr⁺³ ion. 

What visible colour change occurs when aqueous iron (III) salts (Fe⁺³ (aq)) reacts and what’s the reason?

Colour change: Yellow to pale green 

Reason: The yellow brown Fe⁺³ ion forms the pale green Fe⁺² ion. 

What visible colour change occurs when sodium chlorate (I) solution (NaClO) reacts and what’s the reason?

Colour change: Many coloured dyes become colourless. 

Reason: The dyes are oxidized to their colourless forms. 

What visible change occurs when hot concentrated sulphuric acid (H₂SO₄ (L)) reacts and what’s the reason?

Visible change: A pungent colourless gas is evolved

Reason: Sulphur dioxide gas (SO₂) is produced

What visible change occurs when dilute or concentrated nitric acid (HNO₃(aq)) reacts and what’s the reason?

A brown gas is evolved 

Reason: Nitrogen dioxide gas (NO₂) is produced

What are some common reducing agents?

Potassium iodide solution (Kl(aq))

Aqueous iron (ll) salts, Fe²+

Hydrogen sulphide gas H₂S (g)

Concentrated hydrochloric acid (HCl)(aq))

What’s the colour change that occurs when potassium iodide solution reacts and what’s the reason?

Colour change- colourless to brown

Reason- Iodine (I₂) forms which dissolves forming a brown solution

What’s the colour change that occurs when aqueous iron(ll) salts, Fe²+ (aq) reacts and what’s the reason?

Colour change- pale green to yellow- brown

Reason- the pale green Fe²+ ions forms the yellow-brown Fe³+ ion

What’s the visible change that occurs when Hydrogen sulphide gas, H2S (g) reacts and what’s the reason?

Visible change- a yellow precipitate forms

Reason- Solid sulfur (S) forms

What’s the visible change that occurs when concentrated hydrochloric reacts and what’s the reason?

Visible change- A yellow green gas evolved

Reason- Chlorine (Cl₂) gas is produced

What are substances that acts as both oxidizing and reducing agents?

1. Acidified hydrogen peroxide H+/H2O2

2. Sulphur dioxide SO2

what does react with and what are the results?