Video Transcript
When an iron nail reacts with
oxygen and water in the air, it rusts. What happens then to the total mass
of the nail?
We are told that when an iron nail
reacts with oxygen gas and water from the air, it rusts. The water could be water vapor, or
it could be tiny water droplets in the air. Let us have a closer look at how
rusting occurs.
The process of rusting begins when
iron metal dissolves in water, forming iron two plus ions and two electrons. Iron two plus ions are then
oxidized to iron three plus ions. Hydrogen ions are absorbed, and a
reaction with oxygen occurs to produce water along the way. Next, iron three plus ions react
with the water to form iron(III) hydroxide, Fe(OH)3. Finally, hydrated iron(III) oxide,
Fe2O3·𝑛H2O, forms.
Note that these equations shown
here summarize the important steps in rusting but don’t show all the details of
every chemical species involved. This is the reddish brown flaking
material on the surface of old iron metal, which we call rust. Rust is a type of corrosion that
undermines the desirable properties of iron and some iron alloys. Rust is weaker than iron, so
diminishes iron’s mechanical strength and hardness.
The question asked us, what happens
to the total mass of the iron nail as a result of rusting? To answer this question, we need to
determine whether any matter was added or taken away from the iron metal during
rusting. When we compare the formula for
iron and the formula for rust, we see that oxygen and hydrogen atoms have been
added. So the mass of the iron nail will
increase.
In conclusion, what happens to the
mass of an iron nail when it rusts? The answer is the mass
increases.
