5.2 - Batteries

Question 1

Define a battery?

Answer 1

One or more voltaic cells in a single package that generates an electric current.

Question 2

Define a dry cell?

Answer 2

A dry cell is a battery in which the electrolyte is a moist paste.

Question 3

Describe the structure and composition of a typical zinc-carbon dry cell battery?

Answer 3

Structure and composition:

• A carbon (graphite) rod in the center of the dry cell
• Electrolyte paste consists of zinc chloride, manganese (IV) oxide, ammonium chloride, and a small amount of water
• A spacer made of a porous material
• A zinc case

Question 4

Describe the operation of a typical zinc-carbon dry cell battery?

Answer 4

The zinc shell is the anode where the oxidation of zinc occurs

Oxidation half-reaction: Zn_(s)⟶Zn²⁺_(aq)+ 2e^-

The carbon rod is the cathode. It is called an inactive cathode because it is made of a material that does not participate in the redox reaction yet conducts electrons.

The reduction half-reaction occurs in the paste

Reduction half-reaction: 2NH₄⁺_(aq)+ 2MnO_2(s)+ 2e^-→ Mn₂O_3(s) +2NH_3(aq)+ H₂O_(l)

The spacer separates the paste from the zinc anode and acts as a salt bridge.

The voltage produced by a zinc – carbon dry cell = 1.5 V

Question 5

Describe the structure and composition and operation of alkaline batteries?

Answer 5

The anode is made of powdered zinc (to provides more area for reaction) mixed with potassium hydroxide in a paste that is contained in a steel case

The oxidation half-reaction:

Zn_(s)+ 2OH^-_(aq)→ ZnO_(s) +H₂O_(l) + 2e^-

The cathode is a mixture of manganese (IV) oxide and potassium hydroxide

The reduction half-reaction:

MnO_2(s)+ 2H₂O_(l) + 2e^-→ Mn(OH)_2(s) +2OH^-_(aq)

Question 6

True or False:

1) Alkaline batteries are smaller and more efficient than zinc-carbon dry cells.
2) The cathode is made of powdered zinc (to provides more area for reaction) mixed with potassium hydroxide in a paste that is contained in a steel case
3) The anode is a mixture of manganese (IV) oxide and potassium hydroxide

Answer 6

1) T
2) F
3) F

Question 7

What is the half-reduction reaction that occurs at the cathode of a silver battery?

Answer 7

The reduction half-reaction:

Ag₂O_(s)+ H₂O_(l) + 2e^-→ 2Ag_(s) +2OH^-_(aq)

Question 8

What is the half-oxidation reaction that occurs at the anode of a silver battery?

Answer 8

The oxidation half-reaction:

Zn_(s)+ 2OH^-_(aq)→ ZnO_(s) +H₂O_(l) + 2e^-

Question 9

The silver battery is ________ smaller/bigger than the alkaline cell and is used to power devices such as _________, _________, and _________.

Answer 9

1) Smaller
2) hearing aids, watches, and cameras.

Question 10

Differentiate, using examples, between primary and secondary batteries?

Answer 10

Primary batteries produce electric energy by means of redox reactions that are not easily reversed. These cells deliver current until the reactants are gone and then the battery must be discarded

Examples of primary batteries include zinc-carbon, alkaline, and silver batteries.

Secondary batteries produce electric energy using redox reactions that are reversible, so they are rechargeable. While using them, the spontaneous redox reaction occurs producing an electric current. While recharging them, a power source forces the reverse nonspontaneous reaction to occur restoring the original materials in the battery

Secondary batteries are sometimes called storage batteries

Examples of secondary batteries include lead-acid storage batteries (car batteries) and lithium batteries.

Question 11

The lead-acid storage battery is used in ___________.

It consists of ____ cells that generate about ____ V each, for a total output of ____ V.

Answer 11

1) Automobiles
2) 6 cells
3) 2V
4) 12V

Question 12

In a lead-acid storage battery

The anode of each cell consists of ___ or more grids of ________.

The cathode consists of _____ grids filled with __________.

The battery electrolyte is a solution of ___________, and so it is not a dry cell.

Answer 12

1) Two
2) Porous lead
3) Lead
4) lead (IV) oxide
5) Sulfuric acid

Question 13

What is the half-oxidation reaction that occurs at the anode of a lead-acid battery?

Answer 13

Oxidation-half reaction:

Pb_(s)+ SO₄^2⁻_(aq)→ PbSO_4(s) + 2e^⁻

Question 14

What is the half-reduction reaction that occurs at the cathode of a lead-acid battery?

Answer 14

Reduction half-reaction:

PbO_2(s) + 4H⁺_(aq) + SO₄^2-_(aq) + 2e^⁻→ PbSO_4(s) + 2H₂O_(l)

Question 15

What is the overall reaction that occurs in a lead-acid battery?

Answer 15

Overall reaction:

Pb_(s) + PbO_2(s) + 4H⁺_(aq) + 2SO₄^2⁻_(aq) → 2PbSO_4(s) + 2H₂O_(l)

Question 16

Define a lithium battery?

Answer 16

A lithium battery is a battery that oxidizes lithium at the anode.

Question 17

Describe the advantages of a lithium battery?

Answer 17

Because lithium is the lightest known metal and has the lowest standard reduction potential compared to other metals.

Lithium batteries are lightweight, store a large amount of energy for their size, and last much longer than other kinds of batteries

Question 18

________ batteries are lightweight, store a _____ amount of energy for their size, and last much _______ than other kinds of batteries.

Answer 18

1) Lithium batteries
2) large
3) longer

Question 19

What are the uses of lithium batteries?

Answer 19

Lithium batteries are used in watches, computers, and cameras to maintain time, date, memory, and settings even when the device is turned off.

Question 20

Define a fuel cell and describe how fuel cells differ from other batteries?

Answer 20

A fuel cell is a voltaic cell in which the oxidation of fuel is used to produce electric energy.

Fuel cells are provided with fuel from an outside source and so they never run down as batteries do.

They keep producing electricity as long as fuel is available.

Other batteries are either recharged or replaced.

Question 21

Describe the structure, composition, and operation of a fuel cell?

Answer 21

Each electrode is a hollow chamber of porous carbon walls that allow contact between the inner chamber and electrolyte.

A common electrolyte in a fuel cell is a solution of potassium hydroxide.

Question 22

A common electrolyte in a fuel cell is a solution of ________.

Answer 22

Potassium hydroxide

Question 23

What is the half-reduction reaction that occurs at the cathode of a fuel cell battery?

Answer 23

Reduction half-reaction:

O_2(g) + 2H₂O_(l) + 4e^⁻ → 4OH^⁻_(aq)

Question 24

What is the half-oxidation reaction that occurs at the anode of a fuel cell battery?

Answer 24

Oxidation-half reaction:

2H_2(g) + 4OH^⁻_(aq) → 4H₂O_(l) + 4e^⁻

Question 25

What is the overall reaction that occurs in a fuel cell battery?

Answer 25

Overall reaction:

2H_2(g) + O_2(g) → 2H₂O_(l)

Question 26

1) Define corrosion.
2) Identify two substances that must be present for corrosion to occur.
3) What is an example of corrosion?

Answer 26

1) Corrosion is the loss of metal resulting from an oxidation-reduction reaction of the metal with substances in the environment
2) Water and oxygen must be present for corrosion to occur
3) An example of corrosion is the corrosion of iron which is called rusting

Question 27

Describe how rusting occurs?

Answer 27

Rusting is a slow process that occurs over three stages:

1) It begins where there is a small break in the surface of an iron object that is left exposed to air and moisture. This area becomes the anode of the cell as iron oxidizes to iron (II) ions, Fe²⁺_(aq)
2) The lost electrons from iron reduces oxygen into water
3) Fe²⁺ ions in the solution are oxidized to Fe³⁺ ions by reacting with oxygen dissolved in water. The Fe³⁺ ions combine with oxygen to form insoluble Fe₂O₃, which is rust

Question 28

The overall reaction for the corrosion of iron is?

Answer 28

The overall reaction for the corrosion of iron is:

4Fe_(s) + 3O_2(g) → 2Fe₂O_{3 (s)}

Question 29

Describe three methods corrosion can be prevented or minimized?

Answer 29

1) Coating or painting the metal object to seal out both air and moisture.
2) Sacrificial protection:

A more reactive metal than iron such as magnesium, aluminum, or titanium is placed in contact with the iron object. Since these metals are more reactive than iron, they oxidize more readily than iron protecting it from rusting. The sacrificial metal, also called sacrificial anode, is replaced once it is corroded

3) Galvanization:

coating an iron object with zinc by dipping the object into molten zinc or by electroplating the zinc onto it. Zinc is a self-protecting metal that oxidizes readily at the surface, creating a thin metal-oxide coating that protects the zinc from further oxidation.

Galvanization protects iron in two ways:

1- The zinc layer prevents air and moisture from reaching the surface of the iron.

2- When the zinc coating cracks, zinc acts as a sacrificial anode and protects iron by itself being oxidized.

Question 30

Rusting is an example of __________.

Answer 30

Oxidation.