19.3.1 Batteries

Question 1

Batteries

Answer 1

• Batteries are galvanic cells that deliver electrical energy. Batteries are closed systems.
• Lead storage batteries are constructed from lead (at the anode) and lead(IV) oxide (at the cathode).
• Dry cells contain a moist paste, rather than a liquid solution.

Question 2

note

Answer 2

• Batteries are galvanic cells that deliver electrical energy. The anode and cathode of batteries consist of chemicals that are depleted as the battery discharges.
• Lead storage batteries (also known as lead-acid batteries) consist of lead and bisulfate at the anode and lead(IV) oxide, H + , and bisulfate at the cathode.
• Since the overall reaction in lead storage batteries involves only two aqueous components (H + and HSO 4 –), the voltage at any point (E cell ) is determined by Q = 1/([H + ][ HSO 4 –]).
• Lead storage batteries consist of six 2.0 V galvanic cells in parallel, for a total voltage of 12 V.
• One major disadvantage of lead storage batteries is their low energy-to-mass ratio.
• Dry cells contain a moist paste, rather than a liquid solution. Examples of dry cells include Leclanché dry cells, alkaline batteries, mercury batteries, and lithium batteries.
• Leclanché dry cells are constructed with the overall reaction Zn(s) + 2MnO 2 (s) + 2NH 4 +(aq) Zn 2 +(aq) + Mn 2 O 3 (s) + 2NH 3 (aq) + H 2 O(l). Like lead storage batteries, the voltage delivered by Leclanché dry cells changes through the course of the battery’s life.
• Alkaline batteries are similar to Leclanché dry cells, with the overall reaction Zn(s) + 2MnO 2 (s) + H 2 O(l) Zn(OH)2(s) + Mn 2 O 3 (s). However, since only solids and liquids are present in the overall reaction, Q = 1, and E cell = E ̊ cell at any point.
• Mercury batteries are another form of dry cells, with the overall reaction Zn(s) + HgO(s) + H 2 O(l)
  Zn(OH) 2 (s) + Hg(l). Mercury batteries deliver a very steady voltage, but mercury is bad for the environment.
• Lithium batteries are a newer form of dry cells. Lithium batteries are light and deliver a very stable, relatively
  high voltage (3.0 V).

Question 3

Which of the following batteries does not have a stable potential?

Answer 3

Leclanché dry cell

Question 4

Which best describes the electrolyte medium of a Leclanché cell?

Answer 4

Acidic

Question 5

Which of the following occurs during discharge of a lead-acid (storage) battery?

Answer 5

Oxidation of lead and reduction of lead oxide.

Question 6

What comprises the electrolyte of a Leclanché cell?

Answer 6

NH4Cl, MnO2, ZnCl2, and carbon black

Question 7

Which of the following best describes a lead-acid (storage) battery?

Answer 7

Very low energy-to-mass ratio

Question 8

Which can be found in the cathode of a lead-acid (storage) battery?

Answer 8

Lead(IV) oxide

Question 9

What does an alkaline cell have that a Leclanché cell does not?

Answer 9

Increased voltage maintenance

Question 10

Which acid-base reaction occurs in a Leclanché cell?

Answer 10

NH4+ reacting with OH −

Question 11

What is the acid found in a lead-acid (storage) battery?

Answer 11

Sulfuric acid

Question 12

Which best describes a lead-acid cell when its electrodes are coated with PbSO4?

Answer 12

Discharged