Video Transcript
Which of the following suggestions
is not a viable method of slowing or preventing rusting? (A) Painting, (B) plating with tin,
(C) soaking in saltwater, (D) coating with grease, or (E) covering with plastic.
Let’s start by looking at what rust
is and how it’s formed. When iron metal comes into contact
with water and oxygen, rusting begins. Water begins to dissolve the iron
metal, forming iron(II) plus ions and two electrons. Following that, iron two plus ions
are oxidized to iron three plus ions. Along the way, hydrogen ions are
absorbed and water is generated. The iron three plus ions react with
water to generate iron(III) hydroxide. This then reacts with water to form
hydrated iron(III) oxide, which we know as rust.
The overall reaction equation shows
us that iron, oxygen, and water react to produce hydrated iron oxide, which is also
known as rust. Rust builds up over time and can
reduce the strength and stability of an iron object. Iron is usually used because of its
strength and durability, so rust obviously poses a serious problem when using
iron. To prevent rusting or at least slow
it down, oxygen and water must be prevented from coming into contact with the iron
metal.
Knowing this, we can consider the
options given to us in the question. Painting will form a waterproof
layer on the surface of iron. Plating with tin will also form a
layer, and tin is a less reactive metal than iron. Coating with grease will form a
waterproof barrier, and covering with plastic will prevent water from coming into
contact with the iron surface. All of these provide a physical
barrier to water or oxygen or both, slowing or stopping the rusting process.
Soaking in saltwater increases the
rate at which rusting will occur. The process of rusting is a redox
reaction and is influenced by the transfer of electrons. Saline solutions, those which
contain salt, allow electrons to pass more easily. And as a result, iron objects rust
more quickly in saltwater than freshwater. Therefore, the suggestion that is
not a viable method of slowing or preventing rusting is (C), soaking in
saltwater.
