Pure and Impure Substances

In this article, we will tell you the meaning and difference between pure and impure substances. Many people are confused between both of them so, today we will clarify all your doubts and tell the unique properties of both pure and impure substances in great detail. But, before diving deep into this topic let us first understand what substances are?

Substances are materials that are made up of atoms and molecules and have a set of definite properties and compositions. All the elements and pure compounds are substances. The distinguishing quality of substances is their weight and volume. Substances are further categorised into pure and impure substances. 

What are Pure Substances?

Before understanding the key differences between pure and impure substances let’s understand their core meaning.

A pure substance has a constant chemical composition. It is free of impurities or contaminants. They are also commonly referred to as ‘chemical substances’. Pure substances are further categorised into elements and compounds. 

An element is composed of a singular type of atom. It cannot be transferred or broken down into new substances, be it physical or chemical.

They are further categorised into metals, nonmetals or metalloids. Gold and silver are great examples of pure substance. Another example of a pure substance is a solution of salt or sugar in water. The concentration of this solution will always remain the same. This simply means that the number and type of atoms remain constant. At the same time, the phase of matter will also be constant throughout the composition.

Similarly, pure water is also a pure substance since it has the same ratio of hydrogen to oxygen. Any heterogeneous mixture will not be considered a pure substance. According to chemistry, if you can see differences in the composition of material then it is not a pure substance.

A compound is composed of two or more elements combined using chemical means in a fixed defined ratio. These substances can be transferred or broken down into new substances. A good example of a compound is carbon dioxide.

Phases of Pure Substances

A phase can be defined as a distinct molecular arrangement that is homogenous

throughout. At the same time, it can be separated from others by easily identifiable boundary surfaces. 

Now, a substance can exist in different phases within a principal phase, each phase composed of a different molecular structure. For example, carbon may show up as graphite or diamond in the solid phase.

There are three phases of a pure substance. They are as follows:

• Solid

In the solid phase, you will find the molecules arranged in a three‐dimensional pattern (lattice). These molecules cannot move although they oscillate about their equilibrium position.

• Liquid 

The molecule spacing in the liquid phase is almost the same as in the solid phase. The only difference here is that the molecules are no longer at fixed positions.

• Gas

In the gas phase you will see that the molecules are far apart from each other. Additionally, there is no molecular order. Gas molecules move freely anywhere and constantly collide with each other.

What are Impure Substances?

Impure substances are made up of atoms or molecules belonging to different types. They do not have constant composition. They are also known as mixtures. Impure substances can easily be converted to pure substances by using different separation techniques. For example, you can easily separate the mixture of naphthalene balls and common salt using the sublimation method.

Impure substances can be further categorised into homogeneous and heterogeneous mixtures. The homogeneous mixture will always have uniform composition while the heterogeneous mixture will have a varying composition. Some examples of impure substances are as follows:

• Soda: Mixture of water, sugar and added flavours
• Gunpowder: Mixture of sulphur, potassium and carbon nitrate

Difference between Pure and Impure Substances

Conclusion

We hope that after reading this article you can better understand the meaning and key differences between pure and impure substances. The main difference between them is that pure substances are made up of a single element or compound and have constant composition. 

On the other hand, impure substances are made up of atoms or molecules belonging to different types. Another distinguishing feature between them is that pure substances cannot be separated while impure substances can be separated.