Grade 8 Science : Properties of Matter - Part 3

What are Pure Substances and Non Pure Substances?

 

In our everyday life, we use several substances that contain either one or many components. For example, substances such as pure water, sugar, copper and iron contain only one component whereas, substances like air, drinking water, sugar solution and tea possess many components. Tea contains water and sugar in addition to tea while iron consists of iron only. Thus, those matter that have only one component with fixed / definite properties are called pure substances and matter that contain more than one component are called non-pure substances. 

 

• Elements 

Pure substances have a definite composition and when their nature is taken in to consideration, they can be grouped in to elements and compounds. Elements can be cited as the building blocks of all the matter found in our environment and these substances cannot be broken down nor divided in to other substances using physical or chemical methods. Elements portray a series of properties that differ from each other and around 120 elements have been identified.  (Examples: Mercury, Zinc, Sulphur, Copper, Iron). Thus elements are indivisible and they have definite properties. 

 

 

• Compounds

When two or more elements are combined chemically in a fixed/ constant ratio, a compound is formed. This group of pure substances showcase properties that differ from those of the elements. A large number of compounds are present, as elements can be combined in so many ways to form them. Compounds such as water (hydrogen and oxygen), carbon dioxide (carbon and oxygen), copper sulphate (copper, sulphur and oxygen), iron sulphide (iron and sulphur), and sodium chloride (sodium and chlorine) can be elucidated as some examples. The elements are chemically combined to a fixed ratio to form these compounds. These compounds are used in our daily chores too. (Example: Fire extinguishers that are filled with carbon dioxide, Glucose). When we consider the components of air in the atmosphere, oxygen, argon and nitrogen can be cited as elements while carbon-dioxide is formed by the combination of oxygen and carbon chemically. Thus, it consists of more than one element and it can be called a compound. 

 

 

 

 

 

 

 

 

By Mekhala Egodawele

Photo source : Internet