Redox 5: Galvanic & Fuel Cells

Fuels used for energy production, including those used in fuel cells, are substances that can, under the right conditions

• undergo reduction in a spontaneous endothermic reaction
• undergo reduction in a spontaneous exothermic reaction
• undergo oxidation in a spontaneous endothermic reaction
• undergo oxidation in a spontaneous exothermic reaction

A galvanic cell was set up using the Cu²⁺/Cu and Fe³⁺/Fe half-cells. The standard redox potentials for these half-cells are:
Cu²⁺(aq)  +  2e^- →   Cu(s); E⁰ = 0.34 V
Fe³⁺(aq)  +  e^- → Fe²⁺(aq); E⁰ = 0.77 V
The oxidant and reductant reacting in this galvanic cell are, respectively:   

• Fe³⁺; Cu
• Fe²⁺; Cu
• Cu²⁺; Fe³⁺
• Cu²⁺; Fe²⁺

A galvanic cell was set up from a Cl₂/Cl^- half-cell and a standard hydrogen electrode (SHE). It was found that the voltmeter reading was 1.36 V and the chlorine half-cell was the positively-charged electrode. Which statement about this galvanic cell is INCORRECT?

• Both of the electrodes should be made of platinum. 
• The chlorine half-cell is the anode. 
• As the cell operates, the pH of the solution in the SHE decreases. 
• The standard redox potential for the chlorine half-cell must be +1.36 V.

The net cell reaction in a particular galvanic cell is:
Cu²⁺(aq)  +  Sn²⁺(aq) →  Cu(s)  +  Sn⁴⁺(aq)
In this cell, we would expect to observe: 

• crystals of copper forming on the anode.
• the cathode corroding away. 
• the solution in the copper half-cell becoming lighter in colour.
•  the voltmeter needle showing that the copper electrode has negative polarity.

Tags

NGSS.HS-PS2-5

A galvanic cell was set up as shown. 
The standard redox potentials for these half-cells are:
Ag⁺(aq)  +  e^- →  Ag(s);  E⁰ = 0.89 V
Ni²⁺(aq)  + 2e^- →  Ni(s);  E⁰ = -0.23 V
In this cell:

• the silver electrode has positive polarity and the nickel electrode will corrode.
• the silver electrode has positive polarity and the silver electrode will corrode. 
• the silver electrode has negative polarity and the nickel electrode will corrode. 
• the silver electrode has negative polarity and the silver electrode will corrode.

Tags

NGSS.HS-PS1-2

In the ethanol fuel cell, ethanol is pumped in at one electrode and oxygen is pumped in at the other. The only products of the cell reaction are the same as those that would be produced if ethanol was burnt directly in excess air. What is the correct equation for the reaction at the anode, if an acidic electrolyte is used?

• O₂(g) + 4H⁺(aq) + 4e^-→  2H₂O(l) 
• O₂(g)+ 2H⁺(aq) +  2e^- → 2H₂O₂(aq)
• C₂H₅OH(aq) + 3H₂O(l) → 2CO₂(g)  +  12H⁺(aq)  +  12e^- 
• C₂H₅OH(aq) + 3H₂O(l) → 2CO₂(g)  + 11H⁺(aq) +  11e^-

The diagram below shows a hydrogen–oxygen fuel cell that is operating with an acidic electrolyte.
What is Gas X and what is the polarity of electrode N? 

• Hydrogen; positive
• Hydrogen; negative
• Oxygen; positive
• Oxygen; negative

A galvanic cell was set up using the Pb⁴⁺/Pb²⁺ and Pb²⁺/Pb half-cells. The standard redox potentials for these half-cells are:
Pb⁴⁺(aq) + 2e^- →  Pb²⁺(aq); E⁰ = 1.69 V
Pb²⁺(aq)  +  e^- →  Pb(s);  E⁰ = -0.13 V
What metal should be used for the electrode for the Pb⁴⁺/Pb²⁺ half-cell and what would be the potential difference across the cell?

• Lead; 1.56 V
• Lead; 1.82 V
• Platinum; 1.56 V
• Platinum; 1.82 V

Which source of energy involves the least number of energy conversions and hence has greater efficiency? 

• A fuel cell 
• A wind turbine
• A gas-fired power station
• A hydroelectric power station

In a methane–oxygen fuel cell, the net cell reaction is:
CH₄(g)  +  O₂(g)  →  CO₂(g)  +  2H₂O(l)
If an alkaline electrolyte is used, the equation for the reaction at the positive electrode is:

• O₂(g) + 2H₂O(l) + 4e^-→  4OH^-(aq)
• O₂(g) + 4H⁺(aq) + 4e^-→  2H₂O(l)
• CH₄(g) + 2H₂O(l) →CO₂(g) + 8H⁺(aq) + 8e^-
• CH₄(g) + 8OH^-(aq) →CO₂(g) + 6H₂O(l) + 8e^-