We are going to disagree with some other resources we’ve looked at online, and say no, limestone is not a pure substance.
In the article that follows, we’ll explain what a pure substance is, and why it is that we don’t think limestone is a pure substance.
Why Is Limestone a Pure Substance? (Or Not?)
First, What Is A Pure Substance?
To understand how limestone fits in this discussion, we need to first establish what a pure substance is.
A pure substance is a material that is is composed of only one kind of building block.
That building block could be an element (like lead).
That building block could be a compound (like water).
But either way, there is only that one building block, repeated over and over.
If the substances contains other elements or compounds important to its make up, then it is not considered a pure substance.
Next, What Is Limestone?
To have a good discussion, we need to next dissect that limestone is.
Limestone is generally thought to be calcium carbonate CaCO3.
That calcium carbonate compound forms up in more than one way (structure). Calcite is one crystal form, while aragonite is another crystal form.
Limestone deposits tend to contain fossils, as well as other elements or minerals mixed in with it.
Why Isn’t Limestone A Pure Substance?
It is 100% possible for limestone as calcium carbonate to exist in a pure form.
But in reality, this rarely happens.
In most cases, the limestone that you see contains other elements. You might find magnesium (low-magnesium calcite and high-magnesium calcite).
You’ll often find other minerals (such as quartz) mixed in.
You’ll also find fossils and skeletal fragments.
The percentage of the “impurities” from other elements, and items various wildly depending on the limestone deposit.
Because limestone contains impurities (in addition to the calcium carbonate), we don’t think limestone should be called a pure substance.
But Other Resources Call Limestone A Pure Substance….
Sure they do, and they are welcome to.
When limestone means calcium carbonate, and not the stone that you find out in the world, you can call it a pure substance.
Calcium carbonate alone does qualify as a pure substance. It is a compound, and no other element or compound is needed to make it calcium carbonate.
And if you think of calcium carbonate as limestone and vice versa, then you’d be right to think of it as a pure substance.
But you’d also be missing out on quite a bit.
Remember, limestone doesn’t exist out in the world as pure calcium carbonate for the most part, and making it into a pure substance usually requires some kind of processing.
Mostly, this is us making a distinction between calcium carbonate (the compound) and limestone (the material out in the world).
Is Limestone A Mixture?
In general, we think the answer to this question is yes.
A mixture is a material made up of more than one substance, where the substances are in the same physical space without being chemically bonded to each other.
Limestone is made up of calcium carbonate, with a bunch of other impurities (elements and matter) caught up in it.
You’ll find bones, minerals, and other elements mixed into the material, but they are not chemically bonded to it.
Since the materials are not chemically bonded, it should be called a mixture.
Is Limestone a Heterogeneous or Homogeneous Mixture?
Limestone is a heterogeneous mixture.
A heterogeneous mixture is one that is not chemically consistent throughout.
A homogeneous mixture is one that is consistent throughout.
Limestone is a mixture with a bit of this over here, and that over there. In one area of your sample, you might find bones.
In another area, you might find a quartz deposit.
Limestone is rarely consistent (though it can be close), and this is why we’d call it a heterogeneous mixture.
Is Limestone A Compound?
No, limestone is not a compound. Limestone is calcium carbonate with a bunch of other material mixed into it.
A compound is formed when more than one element bonds to another.
The base material of limestone (calcium carbonate) is a compound. But the other items that are mixed into the calcium carbonate are not bonded to it.
Without chemical bonds between the substances, limestone cannot be a compound.
Is Limestone An Element?
No, limestone is not an element.
An element is a substance that cannot be broken down into simpler pieces.
A good example of an element is gold, because gold cannot be broken down into any other elements.
A good example of a material that is not an element is water. Water can be broken down into hydrogen and oxygen.
Limestone is composed of calcium, carbon, and oxygen bonded together. These bonds can be broken and the elements separated. As a result, limestone is not an element.
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