chapter 9.1

Question 1

the origin of the term reduction and the meaning?

Answer 1

• when metal is extracted from raw ore, the mass of the metal is much smaller than the mass of the mined ore
• the process of extracting the metal was historically called reduction – a reduction in the amount of mass

Question 2

how does the term reduction relate to chemical reactions?

Answer 2

• the chemical reactions that removed the metals from the compounds were called reduction reactions.
• there is a relation between reduction reactions and oxidation reactions

Question 3

oxidation

Answer 3

• the loss of electrons
• orginially defined as any reaction in which atom/compound is reacted with molecular oxygen
• later on, saw similarities between reactions of atoms/compounds with oxygen, and reactions of the same atoms/compounds with the elements other then oxygen.

Question 4

1

an example of oxidation reaction

Answer 4

• magnesium and oxygen, magnesium burns very rapidly and emits a very bright light, the product of the reaction is magnesium oxide.
• magnesium oxide is an ionic compound containing magnesium & oxide ions.
• Mg atoms lose two electrons and become positively charged, while O atoms gain two atoms and become negatively charged.

Question 5

2

an example of oxidation reaction

Answer 5

• in solid form the elements exist as separate Mg ions
  -2Mg(s) + O2(g) –> 2Mg2+(s) + 2O2-(s)
• another example can be Mg and Cl
• Mg(s) + Cl2(g) –> Mg2 + 2Cl-(s)
• the product magnesium chloride is also an ionic compound, Mg atoms lose 2 electrons and become ionized, 2 Cl atoms gain one electron each and become negatively charged ions.

Question 6

3

an example of oxidation reaction

Answer 6

• when solid magnesium reacts with either chlorine or oxygen it loses two electrons and becomes a magnesium ion.

Question 7

Oxidation and Reduction

Answer 7

• Oxidation: The loss of electrons.
• Reduction: The gain of electrons
• LEO the lion says GER
• LEO: Loss of Electrons is Oxidation
• GER: Gain of Electrons is Reduction

Question 8

The gain of Electrons

Reduction

Answer 8

• If one atom/ion loses electrons then another atom/ion must gain electron since they cannot exist free in solution.
• Iron ore contains magnetite or hematite, both are iron oxides.
• The process of convertion iron ions to metallic iron involved the addition of electrons to the ions.
• Historically called reduction, chemists now apply the term reduction to all cases in which atoms/ ions gain electrons in a rxn.

Question 9

1

Redox Reactions: up till synthesis

Answer 9

• If one atom/ion is oxidized in a reaction, another must be reduced.
• Reactions in which electrons are gained by an atom/ion and lost by another atom/ion are called Oxidation-Reduction Reactions mostly known as Redox Reactions.
• Redox reactions are not a different set of reactions, they fit into several categories of basic reactions. Oxidation of Mg is considered a synthesis reaction.

Question 10

2

Redox Reactions: starting at decomposition

Answer 10

• Decomposition reactions are the reverse of synthesis reactions, therefore also redox reactions.
• Combustion reactions are when a compound reacts with oxygen, hence also redox reactions.
• Single dis placement reactions are also redox reactions, the reactants and products in SD rxns are often visibly different from each other.
  –> Zinc and Copper
  Zn(s) + CuSO4(aq) –> Cu(s) + ZnSO4(aQ)

Question 11

3

Redox Reactions: ionic equations

Answer 11

• The ionic equation:
  –> Zn(s) + Cu2+(aq) + SO4 2- (aq) –> Cu(s) + ZnSO4 (aq)
• Sulfate ions are spectator ions, ions that are not involved in the reaction. By removing them you get the Net ionic equation
  –> Zn(s) + Cu2+(aq) –> Cu(s) + Zn2+(aq)

Question 12

4

Redox reactions: Zinc and copper

Answer 12

• In this reaction, the zinc atoms lose electrons and undergo oxidation, they are oxidized.
• The copper (II) ions gain electrons and under go reduction, they are reduced.
• Zn(s) + Cu2+(aq) –> Cu(s) + Zn2+(aq)
• Cu2+(aq) -gains 2e-> Cu(s)
• Zn(s) -loses 2e-> Zn2+(aq)
• Since the zinc atoms lose their electrons, the copper ions are responsible for oxidation of zinc atoms.

Question 13

5

Redox Reactions: Oxidizing agents and Reducing agents

Answer 13

• A reactant that oxidizes another reactant is called an oxidizing agent, it receives electrons in a redox reaction, it is reduced.
• Zinc atoms are responsible for the reduction of Copper (II) ions.
• A reactant that reudces anothe reacant is called the reducing agent, it donates or loses electrons in a redox reaction, it is oxidizied.
• A redox reaction can also be defined as a reaction between a oxidizing agent and reducing agent.

Question 14

1

The spontaneity of Redox Reactions

Answer 14

• Zinc Copper (II) Sulfate is a spontaneous redox reaction, it has no addition of energy or any other stimulus.
• Zn displaced Cu in the Cu(II)Sulfate compoundand acted like a reducing agent, and by reducing the Cu ion, the Zn became oxidized.

Question 15

2

The spontaneity of Redox Reactions

Answer 15

• When metallic copper formed it did not replace the zinc ions that had formed, the reaction did not proceed in the reverse direction, which means copper cannot reduce zinc atoms.
• Zn atoms are stronger reducing agents than are Cu atoms, and Cu ions are stronger oxidizng agent than are Zn ions.

Question 16

Predicting the spontaneity of Redox Reactions

Answer 16

• metal ions can act as oxidizing agents because they can remove electrons from certian metal atoms, they also act as reducing agents because they can donate electrons to certain ions.
• Through experiences chemists have determined the strength of many ions as oxidizing agents and many atoms as reducing agents.

Question 17

1

Process of predicting the spontaneity of redox reactions

Answer 17

1. write the net ionic equation
2. add arrows to indicate the gain and loss of electrons
3. identify which of the two metals is the stronger reducing agent, and which of the two ions is the stronger oxidzing agent. (do this through table)
4. if the stronger reducing agent is losing electrons and the stronger oxidizing agent is gaining electrons, the reaction will proceed sponataneously as written.
5. if the stronger reducing agent has gained electrons and the stronger oxidizing agent has lost electrons, the reaction will not proceed sponatneously in the forward direction.

Question 18

2

Process of predicting the spontaneity of redox reactions

Answer 18

• when the stronger reducing agent, and stronger oxidizing agent is on the left side of the equation, the reaction proceeds spontaneously. When they are on the right side of the equation the reaction does not proceed spontaneously.