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.
