Q: A batch of parts is plated with copper in an electrolytic bath running at $$0.15\ \mathrm{V}$$ and $$15.0\ \mathrm{A}$$ for exactly $$2.00$$ hours. What is the total charge passed through the cell?

$$Q = I \times t = 15.0\ \mathrm{A} \times 7200\ \mathrm{s} = 1.08 \times 10^5$\ \mathrm{C}$$

Question 1

Which of the following best describes the process of corrosion in metals?

Accepted Answer

The degradation of metals by chemical reactions with their environment, often involving oxidation and reduction.

Question 2

A clean copper wire is placed into a colorless solution of silver nitrate. Which of the following half-reactions correctly represents the reduction process occurring in this reaction?

Accepted Answer

$$\mathrm{Ag^+(aq) + e^- \rightarrow Ag(s)}$$

Question 3

Which of the following statements about galvanic and electrolytic cells is correct?

Accepted Answer

In a galvanic cell, a spontaneous redox reaction generates electrical energy, while in an electrolytic cell, electrical energy is used to drive a non-spontaneous redox reaction.

Question 4

Given the following standard reduction potentials:

$$\mathrm{Fe$$^{2+}$$(aq) + 2e^- \rightarrow Fe(s)}$$ $$E^\circ = -0.44\ \mathrm{V}$$
$$\mathrm{Cu$$^{2+}$$(aq) + 2e^- \rightarrow Cu(s)}$$ $$E^\circ = 0.337\ \mathrm{V}$$

What is the standard cell potential for a galvanic cell composed of iron and copper electrodes?

Accepted Answer

$$E^\circ_{cell} = 0.337\ \mathrm{V} - (-0.44\ \mathrm{V}) = 0.78\ \mathrm{V}$$

Question 5

Which of the following is the correct cell notation for a galvanic cell where copper is oxidized and silver is reduced, both at 1 M concentration?

Accepted Answer

$$\mathrm{Cu(s) | Cu$$^{2+}$$(aq) (1\ M) || Ag^+(aq) (1\ M) | Ag(s)}$$

Question 6

A galvanic cell is constructed using the following half-cells:

Anode: $$\mathrm{Zn(s) | Zn$$^{2+}$$(aq)}$$ $$E^\circ = -0.763\ \mathrm{V}$$
Cathode: $$\mathrm{Cr$$^{3+}$$(aq) + 3e^- \rightarrow Cr(s)}$$ $$E^\circ = -0.910\ \mathrm{V}$$

What is the standard cell potential and the direction of electron flow?

Accepted Answer

$$E^\circ_{cell} = -0.763\ \mathrm{V} - (-0.910\ \mathrm{V}) = 0.147\ \mathrm{V}$$; electrons flow from Zn to Cr

Question 7

Which of the following best explains why aluminum does not corrode as rapidly as iron, despite having a more negative reduction potential?

Accepted Answer

Aluminum forms a protective oxide layer ($$\mathrm{Al_2O_3}) $$that prevents further corrosion.

Question 8

A batch of parts is plated with copper in an electrolytic bath running at $$0.15\ \mathrm{V}$$ and $$15.0\ \mathrm{A}$$ for exactly $$2.00$$ hours. What is the total charge passed through the cell?

Accepted Answer

$$Q = I 	imes t = 15.0\ \mathrm{A} 	imes 7200\ \mathrm{s} = 1.08 	imes 10^5$\ \mathrm{C}$$

Question 9

Which of the following is NOT a method for preventing corrosion of iron in marine environments?

Accepted Answer

Increasing the concentration of dissolved oxygen in water.

Question 10

In an electrolytic cell, a current of $$2.30\ \mathrm{A} is $$passed for $$15.0$$ minutes to deposit gold from $$\mathrm{Au^+(aq)}. $$What mass of gold is deposited? (Molar mass of Au = $$197\ \mathrm{g/mol}$$, $$F = 96,485\ \mathrm{C/mol})$$

Accepted Answer

$$4.23\ \mathrm{g}$$

Question 11

Which of the following equations correctly relates the standard cell potential to the equilibrium constant $$K$$ for a redox reaction at $$25^\circC$$?

Accepted Answer

$$E^\circ = \frac{0.0592\ \mathrm{V}}{n} \log K$$

Question 12

A tin-plated steel can is scratched, exposing the underlying iron to air and moisture. What type of corrosion is most likely to occur at the scratch?

Accepted Answer

Galvanic corrosion, with iron acting as the anode and corroding rapidly.

Question 13

Which of the following best describes the function of a salt bridge in a galvanic cell?

Accepted Answer

It allows the migration of ions to maintain charge neutrality between half-cells.

Question 14

Which of the following batteries is most suitable for use in a hearing aid due to its high energy density and stability?

Accepted Answer

Zinc-mercuric oxide cell

Question 15

A current of $$2.50\ \mathrm{A} is $$passed through an electrolytic cell for $$5.00$$ minutes. How many moles of electrons are transferred? ($$F = 96,485\ \mathrm{C/mol})$$

Accepted Answer

$$7.78 	imes 10$$^{-3}$$\ \mathrm{mol}$$

Question 16

Which of the following statements about the standard hydrogen electrode (SHE) is correct?

Accepted Answer

It is assigned a potential of exactly zero volts and is used as a reference for measuring other electrode potentials.

Question 17

Which of the following is a correct application of the Nernst equation for a cell at nonstandard conditions?

Accepted Answer

$$E = E^\circ - \frac{0.0592\ \mathrm{V}}{n} \log Q$$

Question 18

In cathodic protection, why is magnesium often used as a sacrificial anode to protect iron structures?

Accepted Answer

Magnesium has a more negative reduction potential than iron, so it oxidizes preferentially, protecting the iron.

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