Unit 6- Redox Reactions

Question 1

Explain the difference between oxidation and reduction reactions

Answer 1

• An oxidation reaction is any reaction in which electrons are lost
• A reduction reaction is a reaction that involves the gain of electrons

Question 2

Explain the difference between the reducing and oxidizing agent

Answer 2

• The element that undergoes oxidation is the reducing agent
• The element that undergoes reduction is the oxidizing agent

Question 3

Why are oxidation and reduction reactions called redox reactions

Answer 3

Oxidation and Reduction reactions must take place concurrently, and therefore they are called redox reactions.

Question 4

What does an oxidation number tell us?

Answer 4

An oxidation number tells us how many electrons an atom in a compound would gain or lose.

Question 5

What type of elements tend to gain/ lose electrons?

Answer 5

Metals have low electronegativity’s and tend to lose electrons to atoms, and are easy to oxidize. Those with high electronegativity’s (non-metals) accept electrons and are reduced.

Question 6

What is the oxidation number of a pure element?

Answer 6

0

Question 7

What oxidation numbers do ions have?

Answer 7

• the oxidation number of most ions is the ion charge
• ions of group 1 metals are assigned the oxidation number +1
• ions of group 2 metals are assigned the oxidation number +2

Question 8

What oxidation number does hydrogen have?

Answer 8

• Hydrogen is assigned the oxidation number +1 in all compounds except metal hydrides, where it is assigned the oxidation number -1 Ex) CaH2

Question 9

What oxidation number does oxygen have?

Answer 9

• Oxygen is assigned the oxidation number -2
• In peroxides like hydrogen peroxide it is assigned -1
• In OF2 it is assigned +2

Question 10

What are the oxidation numbers in covalent compounds?

Answer 10

• In compounds that do not contain hydrogen or oxygen, the more electronegative element is assigned the oxidation number it would have in an ionic compound.

Question 11

Explain the rule about oxidation numbers in compounds

Answer 11

• The sum of oxidation numbers in a compound is zero

Question 12

Explain the rule about oxidation numbers in polyatomic ions

Answer 12

• The sum of oxidation numbers in a polyatomic ion must equal the ionic charge

Question 13

What is electricity in electrochemical cells?

Answer 13

During redox reactions, electrons pass from the oxidized substance to the reduced substance. This flow of electrons is electricity.

Question 14

What are the parts of a simple battery?

Answer 14

Made of two half-cells, each having:
- A metal electrode
- A solution of ions
The half cells are connected via:
- External wire
- Salt Bridge

Question 15

Explain the difference between an anode and a cathode

Answer 15

• Anode: Is where oxidation occurs, making it the negative post. It is the source of electrons.
• Cathode: the site of reduction, the positive post.

Question 16

What is the purpose of the solution of ions in an electrochemical cell?

Answer 16

• It is the source of ions to keep the cell chemically neutral (It is usually the same metal as the electrode with a polyatomic ion acting as a spectator)

Question 17

What is the purpose of the external wire in the electrochemical cell?

Answer 17

The external wire allows the electrons to flow from anode to cathode.

Question 18

What is the purpose of the salt bridge in the electrochemical cell?

Answer 18

• Usually a solution of a group 1 metal and NO3-, SO4-2
• Allows ions to flow between solutions
• Anions go to anode
• Cations go to cathode

Question 19

What happens once the electrochemical cell is connected?

Answer 19

Once connected, the reaction should occur spontaneously. As it proceeds, the concentrations of the ions in solution will reach equilibrium and the cell will become dead.

Question 20

What does the + sign of the cell potential tell us?

Answer 20

That the redox reaction is spontaneous, meaning the cell does work (if you do not get a positive value for the cell voltage you have made a mistake)