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Question Video: Using the Direction of Current in a Hydrogen Fuel Cell to Identify the Electrode Where Oxidation Occurs Chemistry

The diagram is a representation of a hydrogen fuel cell. Considering the direction of electrons through the top circuit, shown by the red arrow, what gas is introduced through pipe A? [A] Oxygen [B] Hydrogen [C] Steam

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Video Transcript

The following diagram is a representation of a hydrogen fuel cell. Considering the direction of electrons through the top circuit, shown by the red arrow, what gas is introduced through pipe A? (A) Oxygen, (B) hydrogen, (C) steam.

Galvanic cells are types of electrochemical cells that produce electrical energy from chemical energy. Galvanic cells can be primary galvanic cells. These cells are for a one-time use only. They may be secondary galvanic cells. Secondary galvanic cells are rechargeable. Fuel cells are a type of primary galvanic cell. Since a fuel cell is continually supplied with reagents, from an external store, it is not discarded like a one-time use battery, where the reagents are depleted. They use coordinated redox reactions to cause electrons to flow in an external electric circuit that powers electrical devices and even electric vehicles.

Let’s look at a diagram of the hydrogen fuel cell. We have a lot of different processes occurring in this diagram. So we will go through it step-by-step. This hydrogen fuel cell is operating in alkaline conditions. It contains a potassium hydroxide salt bridge. On the left we see hydrogen gas diffusing in. The hydrogen reacts with hydroxide ions from potassium hydroxide when the fuel cell is operating under alkaline conditions. It is possible for fuel cells to work under acidic conditions as well, but we should remember that the equations would be different.

On the other side of the diagram, we see oxygen gas diffusing into the cathode. This combines with electrons and water to form more hydroxide ions. Excess oxygen gas, the water product, and heat generated diffuse out of the system. If we look closely at these half-equations, we see oxidation at the anode. We see reduction taking place at the cathode. Water, electrons, and hydroxide ions cancel out in the final overall reaction if we combine our two half-equations.

The diagram from the question is similar to the more detailed version we have looked at earlier. We see the current moving from left to right in the diagram. If the electric current is going from left to right, then the hydrogen gas that provides electrons to the circuit must be diffusing in from the left at the anode. The gas that is introduced from pipe A is hydrogen. This is answer choice (B). Hydrogen is the correct answer.

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