No, soil is not a pure substance, because it contains more than one element or compound.
In the article that follows, we’ll explain what a pure substance is, what soil is, and why soil is not considered a pure substance.
Why Is Soil A Pure Substance? (Or Not?)
To understand why soil does not qualify, you have to first understand what a pure substance is.
Chemically speaking, a pure substance is one that is made up of one kind of building block. That building block can be an element, or it can be a compound.
A good example of a pure substance that is made up of an element is gold.
A good example of a pure substance that is made up of a compound is water. A compound is formed when two or more different kinds of elements form chemical bonds to the other. In the case of water, two hydrogens attach to one oxygen.
Water is made up only these little bundles of hydrogen bonded to oxygen, which we call molecules.
There are no other substances needed or present to make water.
What Is Soil, Exactly?
To understand why soil does or does not qualify as a pure substance, you have to understand what soil is.
And frankly, most people don’t exactly use this term formally.
For most of us, soil is a word that we use to describe or indicate the material we use to grow plants in.
Soil can mean just the dirt over there on the ground, or it can mean the planting mixture you purchased at the local hardware store.
The USDA Natural Resources Conservation Service takes the definition from the Soil Science Society of America:
The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants. (ii) The unconsolidated mineral or organic matter on the surface of the Earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.(source)
The key here for us in the discussion about soil as a pure substance is what the material is made of.
Is there one element, or one compound?
The answer is that soil is very complex (as you can see from the Soil Science Society definition above).
A handful of soil, whether you grab it from the ground or from a commercial store product, is full of a multitude of different substances, in various stages of life or death.
Soil may contain organisms, minerals, and even water.
Since soil is not made up of an element or a compound, it cannot be a pure substance.
Is Soil A Compound?
No, soil is not a compound.
A compound is a material that forms when two or more elements form chemical bonds to join up. There may be multiple different kinds of elements (so that the chemical formula looks like alphabet soup), or there may only be a few.
In the case of soil, you will find any number of materials. Some of these materials may be elements, or even compounds, on their own.
However, since the substances are not chemically bonded to each other, and can easily be separated, soil is not considered a compound.
Is Soil An Element?
No, soil is not an element.
An element is a substance that cannot be broken down into simpler parts.
For example, gold is considered an element because you can’t take it apart or break it down into other substance.
Carbon dioxide is not considered an element because you can break it apart into other substances. It is formed from carbon and oxygen, and the bonds holding those elements can be broken. Once broken, carbon dioxide doesn’t exist.
Is Soil A Mixture?
Yes, soil is considered a mixture.
A mixture is a material made up of more than one substance, where the substances are physical in the same space but not chemically bonded to each other. Even though you might not think so based upon what you see with your eyes, the substances can be separated without the need for a chemical reaction.
Soil is made up of many substances, which are not chemically bonded to each other. You could separate them if you wanted to.
For this reason, soil is a mixture.
Is Soil A Heterogeneous or Homogeneous Mixture?
Soil is a heterogeneous mixture.
A homogeneous mixture is one that is chemically consistent throughout, regardless of where you take your sample.
A heterogeneous mixture is one that is not consistent throughout.
Soil is not chemically consistent throughout. Soil often contains living critters (at the micro level), which may not be found in other areas of the soil.
There may be more water in some areas than others. The water may have more or less or different minerals it in.
Basically, soil is a big hodge podge of stuff and very little of it is consistent enough to be considered a homogeneous mixture.
Although, if a soil was process and mixed enough, we do think it is possible for the mix to be homogeneous. Mostly. It is just unlikely to exist in nature.
Check out our Science Page for our latest posts as we dig deeper and learn more about the world we live on.