when two or more substances (elements or compounds) mix up physically without any fixed ratio by mass, they form a mixture. Mixture is of two types.
HOMOGENOUS MIXTURE: Mixtures that have uniform composition throughout are called homogeneous mixtures e.g. air, gasoline, ice cream.
HETEROGENOUS MIXTURE: heterogeneous mixtures are those in which composition is not uniform throughout e.g. soil, rock and wood.without any fixed ratio, they form a mixture. On mixing up, the component substances retain their own chemical identities and properties.
The mixture can be separated into parent components by physical methods such as distillation, filtration, evaporation, crystallization or magnetization.
Examples: a) Air is a mixture of nitrogen, oxygen, carbon dioxide, noble gases and water vapours. b) Soil is a mixture of sand, clay, mineral salts, water and air.
c) Milk is a mixture of water, sugar, fat, proteins, mineral salts and vitamins.
d) Brass is a mixture of copper and zinc metals.
5) Compound: Compound is a substance made up of two or more elements chemically combined together in a fixed ratio by mass. As a result of this combination, elements lose their own properties and produce new substances (compounds) that have entirely different properties.
Compounds can’t be broken down into its constituent elements by simple physical methods. For example, carbon dioxide is formed when elements of carbon and oxygen combine chemically in a fixed ratio of 12:32 or 3:8 by mass. Similarly, water is a compound formed by a chemical combination between hydrogen and oxygen in a fixed ratio of 1:8 by mass.
Classification of compounds: compounds are of following types.
1) Ionic compounds: Examples: NaCl, KBr, CuSO4.
- Covalent compounds: Examples: H2O, HCl, etc.
- Coordinate covalent compounds: Examples: NH4+, H3O+ .
Some common compounds with their formulae.
|Sodium Chloride (Common Salt)||NaCl|
|Silicon Dioxide (Sand)||SiO2|
|Sodium Hydroxide (Caustic Soda)||NaOH|
|Sodium Carbonate (Washing Soda)||Na2CO3.10H2O|
|Calcium Oxide (Quick Lime)||CaO|
|Calcium Carbonate (Limestone)||CaCO3|
Difference between a Compound and a Mixture
|1||It is formed by a chemical combination of atoms of the elements.||Mixture is formed by the simple mixing up of the substances.|
|2||The constituents lose their identity and form a new substance having entirely different properties from them.||Mixture shows the properties of the constituents.|
|3||Compounds always have fixed composition by mass.||Mixtures do not have fixed composition.|
|4||The components cannot be separated by physical means.||The components can be separated by simple physical methods.|
|5||Every compound is represented by a chemical formula.||It consists of two or more components and does not have any chemical formula.|
|6||Compounds have homogeneous composition.||They may be homogeneous or heterogeneous in composition|
|7||Compounds have sharp and fixed melting points||Mixtures do not have sharp and fixed melting points.|