Regent’s Warm-Up

What is the electron configuration of a sulfur atom in the ground state?

(1) 2 – 4 (2) 2 – 6 (3) 2 – 8 – 4 (4) 2 – 8 – 6

Regent’s Warm-Up

What is the electron configuration of a sulfur atom in the ground state?

(1) 2 – 4 (2) 2 – 6 (3) 2 – 8 – 4 (4) 2 – 8 – 6

Oxidation Reduction Reactions

s AIM: What are Oxidation Reduction Reactions?

Do Now: If the conc. Of a product is increased how will the equilibrium state be affected?

Oxidation Reduction Reactions

What are they used for? Why are they important?… • Purifying metals (e.g. Al, Na, Li) • Producing gases (e.g. Cl

2

, O

2

, H

2

) • Electroplating metals • Electrical production (batteries, fuel cells) • Protecting metals from corrosion • Balancing complex chemical equations • Sensors and machines (e.g. pH meter)

Oxidation Reduction Reactions

Classical Definitions • Oxidation – the combination of a substance with oxygen Example: 2Mg (s) + O 2(g)  2MgO (s) • O 2 is the OXIDIZING AGENT • Mg gains oxygen and is oxidized

Oxidation Reduction Reactions

Classical Definitions • Reduction – the removal of O 2 substance from a Example: CuO (aq) + H 2(g)  Cu (s) + H 2 O (l) • H 2 is the REDUCING AGENT • CuO loses oxygen and is reduced

Oxidation Reduction Reactions

Current Definitions Take into account the charge of the ions and atoms involved in the reaction • Oxidation – the Loss of Electrons Example: 2Mg 0 + O 2 0  2Mg +2 O -2 • The oxidation # of Mg goes from 0 to +2 • Since Mg 0 lost 2e s, Mg 0 is OXIDIZED 2Mg 0  2Mg +2 + 4e -

Oxidation Reduction Reactions

Current Definitions • Reduction – the Gain of Electrons Example: Cu +2 O -2 + H 2 0  Cu 0 + H 2 +1 O -2 • If you look closely oxygen is not reacting, its oxidation # stays the same (-2) • Copper goes from Cu +2 to Cu 0 • Copper gains 2e s & is REDUCED Cu +2 + 2e s  Cu 0

Oxidation Reduction Reactions

What is the MAIN difference between the classical and current definitions?

• Which particles are gained and lost during a redox reaction?

(1) electrons (2) protons *Oxygen is NOT required in the current definition* (3) neutrons (4) positrons

Oxidation Reduction Reactions

• Oxidation and Reduction reactions are opposite processes that occur simultaneously In a redox reaction, how does the total number of electrons lost by the oxidized substance compare to the total number of electrons gained by the reduced substance?

• For something to lose an electron there must be something else that wants to gain that electron

1.

The number lost is always greater than the number gained.

2.

The number lost is sometimes equal to the number gained.

3.

The number lost is always equal to the number gained.

4.

The number lost is sometimes less than the number gained.

Oxidation Reduction Reactions

•

L

oss of

E

lectrons is

O

xidation •

G

ain of

E

lectrons is

R

eduction •

LEO the lion says GER

Oxidation Reduction Reactions

• The substance that loses electrons is OXIDIZED and is the REDUCING AGENT In any redox reaction, the substance that undergoes reduction will • The substance that gains electrons is REDUCED and is the OXIDIZING AGENT

1.

lose electrons and have a decrease in oxidation number

2.

gain electrons and have a decrease in oxidation number

3.

lose electrons and have an increase in oxidation number

4.

gain electrons and have an increase in oxidation number

Oxidation Reduction Reactions

Which half-reaction correctly represents reduction?

Given the balanced ionic equation representing a reaction: 3Mg 2 +(aq)+2Al(s) 2 +(aq)+2Al(s) In this reaction, electrons are transferred from

1.

Ag --> Ag + + e -

2.

Au 3+ + 3e --> Au

3.

F 2 --> 2 F + 2e -

4.

Fe 2+ + e --> Fe 3+

1.

Al to Mg 2+

2.

Al 3+ to Mg

3.

Mg to Al 3+

4.

Mg 2+ to Al

Oxidation Reduction Reactions

Given the balanced equation representing a redox reaction: 2Al + 3Cu 2+ --> 2Al 3+ + 3Cu In any redox reaction, a reactant can undergo a decrease in oxidation number by Which statement is true about this reaction?

1.

Each Al loses 2e gains 3e .

and each Cu 2+

2.

Each Al 3+ loses 3e .

gains 2e and each Cu

3.

Each Al loses 3e gains 2e .

and each Cu 2+

4.

Each Al 3+ loses 2e .

gains 3e and each Cu

1.

losing electrons, only

2.

losing protons, only

3.

gaining electrons, only

4.

gaining protons, only

Oxidation Reduction Reactions

Given the reaction shown: Which species undergoes oxidation?

Which changes occur when Pt 2+ is reduced?

1.

Mg(s)

2.

Cl (aq)

3. 4.

H H + 2 (aq) (g)

1.

The Pt 2+ gains electrons and its oxidation number increases.

2.

The Pt 2+ loses electrons and its oxidation number increases.

3.

The Pt 2+ gains electrons and its oxidation number decreases.

4.

The Pt 2+ loses electrons and its oxidation number decreases