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Pure Substances and Mixtures

Chemistry | 7-14 yrs | Interactive

What is matter?

Matter can be defined as any substance that has inertia, occupies space and has mass.

How is matter classified?

Scientists of the world classify matter as solid, liquid or gas, but there is one more interesting way to classify it. Matter can also be classified as pure substances and mixtures.

What is a pure substance?

A pure substance is a type of matter which exists in its most basic or purest form and cannot be broken down further. Examples of pure substances include water, gases like carbon dioxide, oxygen and metals like platinum, gold and silver.

Each pure substance has its own set of unique chemical and physical properties which helps us in identifying it.

Examples of pure substances

Water has a freezing and melting point of 0°C and a boiling point of 100°C. It is colourless, tasteless and odourless.
Gold is considered pure at 24 karat. It is yellow in color, solid at room temperature and is regarded as a good conductor of electricity. It is also malleable and ductile in nature.

Types of pure substances

Pure substances can be divided into two categories – elements and compounds.
Elements are made up of the same types of atoms. The known elements listed in the periodic table can be considered pure substances. Examples of elements include hydrogen, oxygen, gold, silver
Compounds are made up of different types of atoms joined together by chemical bonds. Examples of compounds include water, glucose, salt and carbon dioxide.

What is a mixture?

Mixture is a combination of two or more pure substances where each substance keeps its own identity upon mixing. Mixtures are present almost everywhere on Earth. Look at rocks, the ocean, rivers or even the atmosphere. All of them are mixtures! In other words, anything that you can mix together is a mixture. Even the foods you eat.

Why is it called a mixture?

It means the fundamental chemical structure of the components in a mixture does not change upon mixing.

Examples of mixtures

Although water is a pure substance, if you put sand into a glass of water, it would turn into a mixture. Each of the components of a mixture can be separated from one another. You can always separate the sand from water by filtering it.

If you take a mixture of salt and water, you can separate it by evaporating the water, to get salt in the container. Air, too, is a mixture of different gases such as carbon dioxide, oxygen, nitrogen and water vapour etc. Blood is a mixture made up of different types of blood cells and plasma.

Types of mixtures

  1. Homogeneous mixture – The components of a homogeneous mixture have a uniform composition, and cannot be seen separately. The prefix ‘homo’ means same and it tells us that when two substances combine extremely well with one another, they form a uniform mixture. For example, sugar and water do not chemically react and form another compound although the water does turn sweet!
  2. Heterogeneous mixture – The components of a heterogeneous mixture do not have a uniform composition and can be viewed separately without losing their identity. For example, if you mix sulfur powder with iron dust, you can easily see the two separately. You can even separate the iron dust by using a magnet.

How do we differentiate between pure substances and mixtures?

  • A Pure Substance is matter which cannot be separated into its basic components by using a physical or a chemical process. The physical and chemical properties of pure substances are non-changing, if it is on its own without disturbing.
  • A Mixture is made up of a combination of two or more substances that are not united using a chemical reaction. The physical and chemical properties of mixtures vary.