No, motor oil 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 motor oil is, and why it is that motor oil does not qualify as a pure substance.
Why Is Motor Oil A Pure Substance? (Or Not?)
What Is A Pure Substance?
Scientifically speaking, a pure substance is one that is made up of one kind of building block.
That building block could be an element, and it could also be a compound.
If the material contains more than one compound that is not bonded to the others, or different elements not bonded to the others, it cannot be a pure substance.
What Is Motor Oil?
Motor oil can be a little complicated.
There are many different kinds of motor oil. Formulations of motor oil differ by who made them, and what the oil is intended to be used for.
But in general, motor oil (also sometimes called engine oil) is made up or two main types of ingredients–oils, and additives. (source)
The base oils are the majority of the product, and they are usually made from natural gas or crude oil.
The additives are where motor oils are differentiated from each other. Chemicals and other products are added the base oil with the goal of making the oil a better and more useful product.
These additives may cause the oil to last longer, protect the engine, improve the flow of the oil, prevent rust from developing, reduce wear on the engine, or even clean up the system as it circulates through while the engine is running.
And don’t get us started on synthetic oil.
Let’s just leave it with the simple fact that synthetic oil is made from many artificially created compounds, which is the most important thing to know to understand whether a substance is a pure substance or not.
The point we need to emphasize here is this–motor oil is made up of multiple substances.
Is Motor Oil A Pure Substance?
No, motor oil is definitely not a pure substance.
The primary and hopefully obvious reason is that commercial motor oil is made up of too many substances.
There are too many elements or too many compounds (or both) that are in the material and not bonded.
For this reason, motor oil is not a pure substance.
Is Motor Oil A Mixture?
Yes, motor oil is more appropriate called a mixture than it is a pure substance.
A mixture is a material composed of multiple substances, where those substances are not bonded to each other.
In most cases, those substances are not bonded, and can be physically separated from each other.
In general, the substances also retain their original characteristics.
Motor oil is a material made up of multiple substances that are not bonded together.
You’ve got the base oil(s), plus any number of additives that exist right alongside and with the oil, but do not become bonded to the oil in any way.
This is why we’d call motor oil a mixture.
Is Motor Oil Heterogeneous Or Homogeneous?
We’d call motor oil a homogeneous mixture.
A homogeneous mixture is one that is chemically and physically the same throughout.
A heterogeneous mixture is one that is not chemically and physically the same throughout.
In the case of motor oil, the oil and base additives are mixed extremely well before they are packaged and sold to the general public.
If you were to sample one area of kind of motor oil, and compare it to another area of the some type and brand of motor oil, those samples should be the same in both composition and appearance.
This is why we call it a homogeneous mixture.
Is Motor Oil A Compound?
No, motor oil is not a compound.
A compound is formed when two different substances (elements, molecules, or compounds) form bonds to each other.
Motor oil contains multiple substances which are not bonded to each other.
Without these bonds, motor oil cannot be a compound, even though it probably contains many different compounds.