Chapter 19 Homework

Question 1

Where does reduction occur in an electrolytic cell?

Answer 1

Cathode

Question 2

Why is zinc used in batteries?

Answer 2

It is a good reducing agent.

Question 3

Mercury dry cell batteries are very stable because all of the phases comprising it are either solid or liquid. Why isn’t the mercury battery more commonly used?

Answer 3

Mercury is a toxic heavy metal and it is not used more often because of the environmental issues.

Question 4

In order for electroplating to work, the reduction potential of the metal must be ___________ the reduction potential for water.

Answer 4

higher than

Question 5

How much current would be required to plate out 25.0 grams of zinc from a 1.0 M solution of zinc chloride in 10.0 hours?

Answer 5

2.05 amperes

Question 6

What is the balanced equation representing the decomposition of hydrogen peroxide in acidic conditions?
H2O2(aq) –> H2(g) + O2(g)

Answer 6

2H+(aq) + 2H2O2(aq) -> H2(g) + O2(g) + 2H2O(l)

Question 7

What is the coefficient on the chromium(III) ion in the properly balanced net ionic equation of the this reaction in acidic solution?
MnO4-(aq) + Cr3+(aq) -> Cr2O72-(aq) + Mn2+(aq)

Answer 7

10

Question 8

Which of the following is the balanced equation for the reaction between the perchlorate ion and iodide ion in an acidic solution?
ClO4- + I- -> Cl- + I2

Answer 8

ClO4- + 8I- + 8H+ -> Cl- + 4I2 + 4H2O

Question 9

What is the pH of a solution used in the following galvanic cell with a potential (Ecell ) of −0.365 V at 25°C?

Ni(s)|Ni2+ (0.1M)||H + (?)|H2(1 atm)

2H+(aq) + Ni(s) <==> H2(g) + Ni2+(aq)

R • T / F = 0.0592 at 25°C

Answer 9

10.5

Question 10

Why is the salt bridge needed between the two half-cells?

Answer 10

To maintain electrical neutrality

Question 11

In the diagram of a galvanic cell, where is oxidation taking place?

Answer 11

A

Question 12

Two half cells are constructed with Fe3+ | Fe in one and Ag+ | Ag in the other. The cells are connected to form a voltaic cell. The standard reduction potential of Fe3+ | Fe is −0.04 V and the standard reduction potential of Ag+ | Ag is 0.80 V. Is the reaction spontaneous? What happens in each compartment?

Answer 12

Reduction: Spontaneous
Oxidized: Fe
Reduced: Ag+

Question 13

Use the standard reduction potentials to calculate the E°cell for the following reaction in a galvanic cell

Mg(s) + 2H+(aq) -> Mg2+(aq) + H2(g)

Answer 13

+2.37 V

Question 14

Use the standard reduction potentials to calculate the E°cell for the following reaction in an electrolytic cell

Cu(s) + Zn2+(aq) -> Cu2+(aq) + Zn(s)

Answer 14

−1.10 V

Question 15

Calculate the reduction potential for the Fe3+ / Fe2+ electrode at 25°C if the concentration of Fe3+ is eight times that of Fe2+

Fe3+ + e− → Fe2+

E ° = +0.77 V.

Answer 15

+0.823 V

Question 16

Calculate the equilibrium constant for the following reaction at 25°C, given that E °cell = +0.67 V

2Cr2+ (aq) + S4O62− (aq) → 2Cr3+ (aq) + 2S2O32− (aq)

Answer 16

4.32 × 10^22

Question 17

The combinations of the half cells shown below are responsible for the the voltage in a lead storage battery commonly used in automobiles. This combination produces about 2 volts. A lead storage battery has a voltage of 12 volts. How is the large voltage accomplished?

Answer 17

A lead storage battery is actually a series of six of these 2 volt cells.

Question 18

Which of the following elements would be least likely to be used in a voltaic cell?

Answer 18

helium

Question 19

How long (in minutes) would it take to deposit 450 mg of sodium in a Downs cell receiving 3.5 A of current?
Faraday’s constant is 96,485 coulombs per mole of electrons
1 A = 1 C/s

Answer 19

9 minutes

Question 20

A galvanic cell with a zinc anode and a copper cathode is allowed to operate for 10 minutes. After 10 minutes, the copper cathode is removed and weighed. Weighing indicates that the mass of the copper electrode has increased by 0.64 grams. What was the average current that flowed through this cell?

Answer 20

3.2 A