Cell Potentials

*These notes were taken from LG 5.3

LG:

file:///C:/Users/Valeska/Desktop/Valeska's%20School%20Files/PSHS%20Grade%2010/Chemistry%202/4th%20Quarter/Learning%20Guides/SLG%20CHEM2%20LG%205.3%20Cell%20Potentials.pdf

Test your knowledge by answering the following:

Part 1: TRUE or FALSE

   Given below are statements about galvanic cells. To check your understanding of galvanic     cells, write TRUE if the statement is correct and FALSE if the statement is incorrect.

Part 2:

1. Write the cell notation for the reaction:

   • 2Al_(s) + 3Pb²⁺_(aq) → 2Al³⁺_(aq) + 3Pb_(s)

2. Given the cell notation, write the anode half-reaction, the cathode half-reaction and the overall balanced equation.

   • Pt_(s) | H_2(g) | H⁺_(aq) || Ag⁺_(aq) | Ag_(s)

Answer Key:

PART I: TRUE or FALSE Statements about Galvanic Cells

1. Oxidation occurs in the anode.
   ✅ TRUE

   • In a galvanic cell, oxidation always occurs at the anode and reduction at the cathode.

2. The anode carries a negative charge.
   ✅ TRUE

   • In galvanic cells (spontaneous reactions), the anode is negative because it supplies electrons.

3. The oxidation number of chemical species decrease at the cathode.
   ✅ TRUE

   • Reduction (gain of electrons) happens at the cathode, which lowers the oxidation number.

4. The standard reduction potentials are measured at room temperature.
   ✅ TRUE

   • Standard conditions for electrochemical measurements are 25°C (298 K), 1 atm, and 1 M solutions.

5. Electrons flow from the anode to the cathode through the salt bridge.
   ❌ FALSE

   • Electrons flow through the external wire, not the salt bridge. The salt bridge allows ion flow to maintain charge balance.

6. The electrode potentials are measured relative to the standard hydrogen electrode.
   ✅ TRUE

   • All standard electrode potentials are referenced against the standard hydrogen electrode (SHE), which is assigned 0.00 V.

7. E°cell are written as reduction half-reactions.
   ✅ TRUE

   • Standard electrode potentials (E°) are tabulated for reduction half-reactions.

8. The anode has the more positive the E° half-cell.
   ❌ FALSE

   • In a galvanic cell, the cathode has the more positive E° value; electrons flow from lower to higher potential.

9. For the oxidation half-reaction, the value of the E° half-cell is reversed.
   ✅ TRUE

   • When using standard reduction potentials to calculate E°cell, reverse the sign of E° for oxidation.

10. The more positive the E°cell, the stronger the oxidizing agent.
    ✅ TRUE

• A more positive E° indicates a greater tendency to gain electrons, making it a stronger oxidizing agent.

PART II: Electrochemical Cell Notation and Equations

1. Write the cell notation for the reaction:

2Al(s)+3Pb(aq)2+→2Al(aq)3++3Pb(s)2Al_{(s)} + 3Pb^{2+}_{(aq)} \rightarrow 2Al^{3+}_{(aq)} + 3Pb_{(s)}

Step-by-step:

• Anode (oxidation): Al(s)→Al(aq)3++3e−Al_{(s)} \rightarrow Al^{3+}_{(aq)} + 3e^-

• Cathode (reduction): Pb(aq)2++2e−→Pb(s)Pb^{2+}_{(aq)} + 2e^- \rightarrow Pb_{(s)}

• Cell notation format:
  Anode ∣ Anode solution ∣∣ Cathode solution ∣ Cathode\text{Anode} \ | \ \text{Anode solution} \ || \ \text{Cathode solution} \ | \ \text{Cathode}

Answer:

Al(s)∣Al(aq)3+ ∣∣ Pb(aq)2+∣Pb(s)Al_{(s)} | Al^{3+}_{(aq)} \ || \ Pb^{2+}_{(aq)} | Pb_{(s)}

2. Given the cell notation, identify the reactions:

Cell notation:

Pt(s)∣H2(g)∣H(aq)+ ∣∣ Ag(aq)+∣Ag(s)Pt_{(s)} | H_2(g) | H^+_{(aq)} \ || \ Ag^+_{(aq)} | Ag_{(s)}

Interpretation:

• Left side (anode): H2(g)→2H+(aq)+2e−H_2(g) \rightarrow 2H^+(aq) + 2e^- (oxidation)

• Right side (cathode): Ag+(aq)+e−→Ag(s)Ag^+(aq) + e^- \rightarrow Ag(s) (reduction)

• Balance the reaction: Multiply Ag⁺ reaction by 2 to match electrons

Overall balanced equation:

H2(g)+2Ag+(aq)→2H+(aq)+2Ag(s)H_2(g) + 2Ag^+(aq) \rightarrow 2H^+(aq) + 2Ag(s)

Answers:

• Anode half-reaction:
  H2(g)→2H+(aq)+2e−H_2(g) \rightarrow 2H^+(aq) + 2e^-

• Cathode half-reaction:
  2Ag+(aq)+2e−→2Ag(s)2Ag^+(aq) + 2e^- \rightarrow 2Ag(s)

• Overall equation:
  H2(g)+2Ag+(aq)→2H+(aq)+2Ag(s)H_2(g) + 2Ag^+(aq) \rightarrow 2H^+(aq) + 2Ag(s)