Chapter 21, Problem 3STP

Interpretation Introduction

Interpretation: The product of the reaction that occurs in a hydrogen-oxygen fuel cell needs to be identified.

Concept Introduction: In an electrolytic cell, oxidation takes place at the anode and reduction takes place at the cathode. In oxidation, electrons are released and in reduction, electrons are added to the reactant. The oxidation state of the reactant increases during oxidation and decreases during reduction.

Answer to Problem 3STP

The correct answer is option (C)

Explanation of Solution

Reason for the correct option:

In the hydrogen-oxidation fuel cell, hydroxide ions from KOH are used to carry current. Here, hydroxide ions contain oxygen and water is formed at the anode. The dissociation of KOH electrolyte is represented as follows:

  $\text{KOH}\rightleftharpoons {\text{K}}^{+}+{\text{OH}}^{-}$

Here, hydrogen (neutral) at the anode reacts with hydroxide ions to form water. The reaction is represented as follows:

  $2{\text{H}}_{\text{2}}+4{\text{OH}}^{-}\to 4{\text{H}}_{\text{2}}\text{O}+4e$

Similarly, at the cathode, hydroxide ions are regenerated by the electrons.

  ${\text{O}}_2+2{\text{H}}_{\text{2}}\text{O}+4e\to 4{\text{OH}}^{-}$

The overall cell reaction will be:

  ${\text{2H}}_{\text{2}}+{\text{O}}_2\to 2{\text{H}}_{\text{2}}\text{O}$

Here, the product formed is water. Therefore, option (C) is correct.

Conclusion

Reason for incorrect options:

In the hydrogen-oxygen fuel cell, carbon is not involved thus, carbon dioxide and carbon monoxide cannot be the products.

Also, hydrogen peroxide is formed when 2 mol of hydrogen gas reacts with 2 mol of oxygen, in the overall reaction in a hydrogen-oxygen fuel cell, the ratio of the number of moles of hydrogen gas and oxygen gas in the reactant side is 2:1.

Therefore, options (A), (B), and (D) are incorrect options.