No, milk is not a pure substance.
In the article that follows, we’ll explain what a pure substance is, and why it is that milk does not qualify.
Why Is Milk A Pure Substance? (Or Not?)
First, let’s talk about what a pure substance is (or is not).
A pure substance is any material that is made up of one kind of building block.
That building block could be an element.
An element is any substance which cannot be broken down or apart into more simple substances.
A good example of an element is gold. Gold cannot be broken apart into other substances, like oxygen and hydrogen, the way water can.
Gold is just gold.
That building block could also be a compound.
A compound is made when two other substances (element, molecule, or even a compound) form bonds to another element, molecule, or compound.
A good example of a compound is water. It is hydrogen and oxygen bonded together.
If the material or substance is not made up of either a single kind of element or a single kind of compound, it is not a pure substance.
For example, if the material is made up of gold and water, but the gold and water are not bonded to each other, the substance is not a compound, and is therefore not a pure substance.
Some other examples of pure substances are: pure water, lead, baking soda, hydrogen gas, ammonia, iron, salt, silver, sugar, diamond, sulfur, tin, and carbon dioxide.
Next, Let’s Talk About What Milk Is
Milk looks pretty simple when you observe it in a glass or jug. It is a whitish liquid, and when you look at it with your plain eyes, there is nothing interesting to be seen in most cases aside from a few bubbles.
Milk is actually quite complicated.
Milk is mostly water, with tons of tiny blobs floating around in it. Milk contains fat, lactose, protein, vitamins, minerals, and enzymes, among other substances.
The tiny blobs are made up of the fat, lactose, protein and the rest.
The percentages and composition of the milk also depends upon the species of animal that provided the milk, as well as that particular animal’s health, nutrition and food, and stage of lactation. (source)
We actually call milk “a colloid” because of the way that the tiny blobs behave in the water.
Instead of floating to the bottom of the glass like dirt or sand would, the fat blobs just stay where they are, suspended in the water, and then stay pretty evenly distributed throughout the mixture.
When you look at the milk from the top, the sides, and the bottom, it pretty much looks the same, consistent and homogeneous.
So, Is Milk A Pure Substance Or Not?
Milk does not qualify as a pure substance.
If you recall as we defined what a pure substance is, a pure substance must be made up of only one kind of element or compound.
If there is more than one kind of element or compound, the substance is not a pure substance.
Milk fails the pure substance inquiry because it is made up of more than one element or compound.
Milk is made up of water and many other substances including fat, proteins, and minerals. This is is several separate substances that are not bonded to each other, much more like you’d expect of a mixture than of a pure substance.
Because milk has too many building blocks, it is not considered a pure substance.
Could Milk Be Made Into A Pure Substance?
To change the material that is milk into a pure substance, you’d have to somehow strip out everything but one element or compound. If you stripped everything away but the water, you wouldn’t have milk.
You’d have water.
The same is true if you stripped out the water, lactose, and fat, to try and leave just one mineral.
What you’d have in the end isn’t milk…it would just be the mineral.
Check out our Science Page for our latest posts as we dig deeper and learn more about the world we live on.