Question

QUESTION 0.5 pointsSave Answer What is the standard cell voltage in volts for a voltaic cell comprising Al as one electrode and inert Pt as the other electrode? Oxygen gas is bubbled onto the Pt electrode in acidic solutions. Hint: cathodic reaction does not involve Pt, it is oxygen reduction reaction, so find t in the table of standard reduction potentials for acidic solutions. a 2.89 C c C 3.8 d-3.8 e-4.0 Се. QUESTION 2 0.5 points Save Answer What is the cell voltage in V for the electrolysis of water at temperature of 120℃ H2 pressure 0.4 atm, O2 pressure 0.2 atm and water vapor pressure is 1 atm? Hint: the sign of the cell voltage determines if the reaction is galvanic or electrolytic Ca. b.1.23 C c. C-1.09 C d.

Answer 1

1. Cathode

O2(g) + 4 H++ 4 e−

⇌

2H2O

+1.229V

Anode

Al3+ + 3 e−

⇌

Al(s)

−1.662 V

E°cell = 1.229 - ( - 1.662) = 2.891 V

2. Reduction at cathode: 2 H⁺(aq) + 2e⁻ → H₂(g) E°= -2.23 V

Oxidation at anode: 2 H₂O(l) →O₂(g) +4 H⁺(aq) + 4e⁻ E°= -1.0V

Combining either half reaction pair yields the same overall decomposition of water into oxygen and hydrogen:

Overall reaction: 2 H₂O(l) → 2 H₂(g) + O₂(g)

Ecell = E°cell -2.303 RT/nF Log [pO2][pH2]² / [pH2O]²

Ecell = -2.23 -(-1.0) -2.303 × 8.314 × 393.15 / 4 × 96485 × Log (0.2× 0.4/1)

Ecell = -1.208 V