Question

Definition of pure substances and mixtures.

Answer 1

One must know that all matters that exist can be categorized into pure substances and impure substances. Pure substances are classified as elements and their compounds. Often, impure substances are also classified as mixtures.

Complete answer:
Pure substances:
Substances that only have one kind of particle and have a constant or a fixed structure are known as pure substances.
Substances that cannot be further broken down into simpler substances are known as elements. One can not transform an element into a new element by using any chemical or physical means. For example, gold, iron, diamond, copper, etc.
There are 118 total recognized elements and can be categorized further into metals, nonmetals, and metalloids. 94 of these elements occur naturally on Earth whereas the rest 24 are formed during nuclear reactions.
Now, substances that can be further broken down into simpler substances are known as compounds. Compounds can be broken down into simpler substances by chemical methods.
When two or more atoms of different elements combine in a fixed ratio chemically, compounds are formed. For example, steel, water, salts, carbon dioxide, etc.
Mixtures:
Substances that have more than one kind of particles, not necessarily in a fixed ratio, and combined physically are known as mixtures.
Mixtures can contain different substances, different compounds, or even different states of matter. For example, air, ink, blood, soda, etc.
The different components of a mixture can be easily extracted and separated from the mixture by either physical methods like distillation or filtration or chemical methods.
Mixtures can further be classified into homogeneous and heterogeneous mixtures.
Mixtures that have the same properties and compositions throughout their mass are known as homogenous mixtures. All the units of a homogeneous mixture are the same. For example, sugar mixed in water, most alloys, saline solutions, etc.
Mixtures that have different properties and compositions at different parts of the mass are known as heterogeneous mixtures. The units of a heterogeneous mixture are not uniform. For example, concrete, pizza, seawater, etc.

Note:
It should be noted that in contrast to pure substances, there is often very little or no change in the energy upon formation of mixtures. Also, pure substances have constant physical and chemical properties whereas they vary for mixtures.