No, aluminum foil is not a pure substance.
In the article that follows, we’ll explain what aluminum foil is and how aluminum foil does not qualify as a pure substance.
Why Is Aluminum Foil A Pure Substance (Or Not)?
First, let’s talk about what a pure substance is.
A pure substance is a substance that is made up of one kind of building block. That building block could be one kind of atom, one kind of molecule, or one kind of compound.
Gold is a good example of a pure substance that is made up of one kind of atom.
Breathable oxygen is a good example of a building block that is a molecule, but contains the same kind of atoms. Generally two oxygen atoms bond together to form O2.
A carbon dioxide is a good example of a building block that is a compound. Carbon dioxide is made up of carbon and oxygen bonded together. This differs from O2 in that there are different kinds of materials that make up this molecule.
But carbon dioxide gas qualifies as a pure substance because the only thing necessary to make CO2 gas is carbon dioxide molecules, on repeat.
An example of a substance that is not a pure substance is seawater. Seawater looks like a consistent substance, but at a molecular level, it contains many different kinds of substances: water, salt, dissolved minerals, particulate matter, and pollution.
What Is Aluminum Foil?
The next step to understanding why aluminum foil qualifies (or doesn’t) as a pure substance, is to understand what aluminum foil is made up of, and how aluminum foil is made.
Aluminum is an elemental metal. As a element, aluminum exists as a substance that cannot be broken down into simpler substances (like water can be broken apart into hydrogen and oxygen). Aluminum is a pure substance.
But on Earth aluminum is rarely found in the pure substance state. Instead, it is generally found (and mined) mixed with other substances (such as silica, iron oxide, and other metals).
To make aluminum foil, the aluminum must first be extracted/removed from the mix it was mined with. This is done by a combination of refining and smelting.
Once the aluminum has been refined and smelted, it is pressed and rolled into the aluminum foil we know and purchase at the local store.
Yet, even with all of the refining and smelting, it is rare for the finished product to be 100% aluminum. In most cases, the resulting product rolled into commercial foil still contains traces amounts of other materials that were originally mixed into the ore.
Aluminum foil can be as much as 99% aluminum, but in other cases, it might only be as much as 92% aluminum. (source)
This will depend heavily on the original ore used to make the foil, as well as the unique process employed by the particular manufacturer.
To sum, since the aluminum foil is not just the elemental aluminum, the foil itself does not qualify as a pure substance.
And for argument’s sake, it is important to acknowledge that aluminum foil could be a pure substance, and completely made up of nothing else but aluminum metal.
It just isn’t.
Is Aluminum Foil A Mixture?
Yes, aluminum foil is a mixture.
A mixture is a material that is made up of more than one substance. These substances are not chemically bonded to each other. They can be separated without the need for a chemical reaction.
Aluminum foil is mostly aluminum, but not quite. It contains trace elements of metals and other minerals, depending on where the aluminum ore was originally mined. The refining and smelting process does not quite remove all of the traces, leaving them in the foil at a molecular level.
Since these substances are not chemically bonded to the aluminum foil, the resulting substance is a mixture.
Theoretically, aluminum foil could not be a mixture, if the aluminum ore used to make the foil was sufficiently refined to remove impurities.
But since that rarely happens, the foil is a mixture.
Is Aluminum Foil A Heterogeneous Mixture or a Homogeneous Mixture?
A heterogeneous mixture is a mixture that is not chemically consistent throughout. A homogeneous mixture is one that is chemically consistent throughout.
We take the position that aluminum foil, given the amount of refining and processing it undergoes, is a homogeneous mixture. If you were to take a sample of the foil at the beginning of the roll and also at the end, the chemical composition would be the same.
If there were impurities in the foil (and there will be), they will be in the same amount and kind regardless of where you take the sample.
Is Aluminum Foil An Element?
No, aluminum foil is not an element.
An element is a substances which cannot be broken down into simpler parts.
Aluminum foil is made with aluminum, mostly aluminum. But because it contains impurities, the foil can be broken down into aluminum and its impurities.
If the foil was perfectly refined aluminum, you could call it an element. But in general, foil is rarely if ever pure.
Is Aluminum Foil Pure Aluminum?
While it is possible for aluminum foil to be pure aluminum, this rarely, if ever, happens.
In most cases, foil is mostly aluminum, with other trace minerals or metals mixed in that were not removed during the refining process.
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