Part (a) - Difference between Pure and impure substances
- Pure materials have a known composition as well as known physical and chemical characteristics.
- All pure substances are homogenous, meaning that the majority of them have a constant composition.
- Sharp melting and boiling points are characteristics of pure substances.
- Examples: gold, copper, oxygen
Elements - Because they only contain one kind of atom, elements are referred to as pure substances. Currently, the periodic table has around 118 elements.
Compounds are created when multiple elements combine chemically in a predetermined ratio. Chemical reactions can change pure molecules into brand-new substances.
- Two or more pure substances combined in any ratio create an impure compound.
- They can either be homogeneous or heterogeneous, meaning that the bulk of their makeup is not the same.
- They are all mixtures.
- Examples: air, seawater, petroleum, and a solution of sugar in water are all impure substances.
Part (b) - Difference between Homogeneous and heterogeneous substances
- When the elements that make up a combination are evenly distributed throughout the mixture, the mixture is said to be homogenous.
Example: Air, Sugar water, Rainwater.
- A mixture is considered heterogeneous if any of its constituent parts are not uniform or have distinct localised zones.
Example: Cereal in milk, Vegetable soup.
Difference between: (a) Pure and impure substances (b) Homogeneous and heterogeneous substances
(a) While impure substances are formed of two or more substances blended in any proportion, pure substances have specific chemical and physical properties and composition.
(b) In contrast to heterogeneous mixtures, homogeneous mixtures have evenly distributed mixtures.