Video Transcript
In old brick limekilns, such as
the one in the picture, large quantities of limestone were continually added and
heated to very high temperatures. What was the main waste gas
that escaped through the chimney? What solid limestone derivative
was collected from holes in the bottom of the kiln?
This question is asking about a
reaction involving limestone, also known as calcium carbonate. While the limestone pulled from
the earth does have other minerals in it, it is composed primarily of calcium
carbonate. For that reason, in chemistry,
we use the terms limestone and calcium carbonate interchangeably. Another clue about the nature
of this chemical reaction is that the limestone is being heated. When a chemical reaction
requires heat to proceed, we may write the reaction arrow with the 𝛥 symbol
above it to signify that heat is being added. We might also see the word heat
in place of the 𝛥.
The two parts of this question
are asking about the substance that escaped or the substance that was collected
at the end of the reaction. In other words, this question
is asking, what are the products of this chemical reaction? We may be familiar with this
reaction because it’s part of the lime cycle. The lime cycle consists of
products related to limestone and the reactions that create them. The reaction that’s part of the
lime cycle that involves heating limestone creates carbon dioxide and calcium
oxide as products. We call a reaction like this
thermal decomposition because we’re using heat to break down a compound into
multiple products.
But the question remains, which
product corresponds to which part of the question? Well, the waste gas is carbon
dioxide. When carbon dioxide is
produced, it is almost always as a gas and not as a solid like the other part of
the question would suggest. So our answer to the first part
of the question is carbon dioxide.
Next, which product is a solid
limestone derivative? That’s the other product,
calcium oxide. As we move around the lime
cycle, we obtain a variety of limestone derivatives. The thing that they have in
common is that they all contain calcium. So the solid limestone
derivative that the second part of the question is asking about is calcium
oxide, which we can write in as our answer. Another name for calcium oxide
is quicklime. It’s not necessary to include
the name quicklime in our answer. But it’s important to recognize
that calcium oxide and quicklime are different names for the same substance.
Because it can be easily
created by heating naturally occurring minerals, the use of quicklime as a
construction material dates back quite far, at least 6000 years. Quicklime was used in mortars
and plasters to create the pyramids of Egypt, the Roman aqueducts, and the Great
Wall of China, among other historical structures. So in brick limekilns, such as
the one in the picture, what was the main waste gas that escaped through the
chimney? That’s carbon dioxide. And what solid limestone
derivative was collected from holes in the bottom of the kiln? That’s calcium oxide, also
known as quicklime.
