Q: A galvanic cell is constructed using the reaction $$2\mathrm{Al(s) + 3Cu$$^{2+}$$(aq) \rightarrow 2Al$$^{3+}$$(aq) + 3Cu(s)}$$ with $$E_{cell} = 0.500\ \mathrm{V}. If$$ $$1.00\ \mathrm{g} of $$aluminum is used, what is the maximum electrical work ($$w_{max}) $$obtainable? ($$F = 96,485\ \mathrm{C/mol}$$, $$M_{Al} = 26.98\ \mathrm{g/mol})$$

$$w_{max} = 5.36 \times 10^3$\ \mathrm{J}$$

Question 1

Which of the following statements best describes the first step in balancing a redox reaction in either acidic or basic solution?

Accepted Answer

Identify the oxidizing and reducing agents by assigning oxidation numbers.

Question 2

In the reaction $$\mathrm{Fe$$^{2+}$$(aq) + NO_3$^-(aq) \rightarrow Fe$$^{3+}$$(aq) + NO(g)}$$ under acidic conditions, what is the correct oxidation number change for nitrogen?

Accepted Answer

From +5 to +2

Question 3

When balancing a redox reaction in acidic solution, which is the correct order of steps after splitting into half-reactions?

Accepted Answer

Balance all atoms except H and O, balance O by adding $$\mathrm{H_2O}$$, balance H by adding $$\mathrm{H^+}$$, then balance charge by adding electrons.

Question 4

Given the half-reaction $$\mathrm{Cr_2O_7$$^{2-}$$(aq) \rightarrow 2Cr$$^{3+}$$(aq)} in $$acidic solution, what is the correct balanced half-reaction including all species?

Accepted Answer

$$\mathrm{14H^+(aq) + Cr_2O_7$$^{2-}$$(aq) + 6e^- \rightarrow 2Cr$$^{3+}$$(aq) + 7H_2O(l)}$$

Question 5

Which of the following is the correct procedure to convert a balanced redox reaction from acidic to basic conditions?

Accepted Answer

Add $$\mathrm{OH^-} to $$both sides for each $$\mathrm{H^+}$$, combine $$\mathrm{H^+}$$ and $$\mathrm{OH^-} to $$form $$\mathrm{H_2O}$$, then cancel $$\mathrm{H_2O} on $$both sides.

Question 6

In the reaction $$\mathrm{Pb(OH)_3^-(aq) + ClO^-(aq) \rightarrow $$PbO_2$$(s) + Cl^-(aq) + H_2O(l) + OH^-(aq)}$$ under basic conditions, what is the oxidation state change for lead?

Accepted Answer

From +2 to +4

Question 7

A galvanic cell is constructed using the reaction $$2\mathrm{Al(s) + 3Cu$$^{2+}$$(aq) \rightarrow 2Al$$^{3+}$$(aq) + 3Cu(s)}$$ with $$E_{cell} = 0.500\ \mathrm{V}. If$$ $$1.00\ \mathrm{g} of $$aluminum is used, what is the maximum electrical work ($$w_{max}) $$obtainable? ($$F = 96,485\ \mathrm{C/mol}$$, $$M_{Al} = 26.98\ \mathrm{g/mol})$$

Accepted Answer

$$w_{max} = 5.36 	imes 10^3$\ \mathrm{J}$$

Question 8

Which equation correctly relates the standard cell potential to the standard free energy change?

Accepted Answer

$$\Delta G^\circ = -nFE_{cell}$$

Question 9

If the reduction potential for the cathode is $$0.34\ \mathrm{V}$$ and for the anode is $$-0.76\ \mathrm{V}$$, what is the standard cell potential ($$E_{cell}$$)?

Accepted Answer

$$E_{cell} = 0.34\ \mathrm{V} - (-0.76\ \mathrm{V}) = 1.10\ \mathrm{V}$$

Question 10

Which of the following best describes the role of the anode in an electrochemical cell?

Accepted Answer

It is where oxidation occurs and electrons are released.

Question 11

In the half-reaction $$\mathrm{Zn(s) \rightarrow Zn$$^{2+}$$(aq) + 2e^-}$$, what is being oxidized and what is the change in oxidation number?

Accepted Answer

Zn is oxidized from 0 to +2

Question 12

Which of the following is true about the relationship between cell potential and the spontaneity of a reaction?

Accepted Answer

A positive $$E_{cell}$$ indicates a spontaneous reaction.

Question 13

Which of the following is the correct balanced overall reaction for the dichromate and zinc reaction in acidic solution?

Accepted Answer

$$\mathrm{3Zn(s) + 14H^+(aq) + Cr_2O_7$$^{2-}$$(aq) \rightarrow 3Zn$$^{2+}$$(aq) + 2Cr$$^{3+}$$(aq) + 7H_2O(l)}$$

Question 14

Which of the following best explains why electrons are added to balance charge in half-reactions?

Accepted Answer

To ensure the total charge is the same on both sides of the half-reaction.

Question 15

A student is asked to balance the following redox reaction in basic solution: $$\mathrm{$$MnO_4$$^-(aq) + Fe$$^{2+}$$(aq) \rightarrow $$MnO_2$$(s) + Fe$$^{3+}$$(aq)}. $$Which step must be performed after balancing the reaction as if it were in acidic solution?

Accepted Answer

Add $$\mathrm{OH^-} to $$both sides for each $$\mathrm{H^+}$$, then combine to form $$\mathrm{H_2O}.$$

Question 16

Which of the following correctly expresses the relationship between the equilibrium constant $$K$$ and the standard cell potential $$E_{cell}^\circ$$?

Accepted Answer

$$E_{cell}^\circ = \dfrac{RT}{nF} \ln K$$

Question 17

Which of the following is the correct expression for the maximum electrical work ($$w_{max}) $$obtainable from an electrochemical cell?

Accepted Answer

$$w_{max} = -nFE_{cell}$$

Question 18

Which of the following best describes the meaning of a standard reduction potential?

Accepted Answer

It measures the tendency of a species to gain electrons under standard conditions.

Electrochemistry: Balancing Redox Reactions and Cell Potentials

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