Lecture 1 – Pure substances & Mixtures

METHODS OF PURIFICATION:

Pure substances:

Pure substances have only one type of atom or molecule in them.

1. Elements are pure substances that contain only one type of atom.
• Example: Iron, Aluminium, Sodium, etc
2. Compounds are pure substance that contain only one type of molecule.
• Example: Sodium chloride, Oxygen, Water, Carbon dioxide

 Mixtures:

Mixtures are a physical combination of one or more pure substances.

Examples:

1. Alloys: Alloy are mixtures of metals with the metal containing some other metal or non – metal like Carbon, Oxygen or Suplhur.
• Brass is an alloy of Copper and Zinc
• Steel is an alloy of Iron and Carbon
2. Air is a mixture of Nitrogen, Oxygen, Carbon dioxide, Water vapour, Argon and other noble gases.
3.  Crude oil is a mixture of Petrol, Methane, Naphta, Kerosene, etc.

Table 4: Differences between Compound and Mixtures.

Mixtures	Compounds
Mixtures can be separated by physical means	Compounds cannot be separated by physical means
Physical properties are intermediate between that of the constituent elements	Physical properties are entirely different from the constituent elements
Little or no energy is exchanged while making mixtures	Energy is usually evolved and sometimes absorbed while making compounds
Chemical properties of the constituent elements remain unaffected in mixtures	Chemical properties are entirely different from the constituent elements

Melting and Boiling points: A test of impurity.

Pure substances have sharp melting and boiling points. Impure substance have a range of melting and boiling points. Thus, sharp melting and boiling points determines the purity of the substances.

Table 5: Simple terminologies

Term	Definition
Solute (noun)	Solid that dissolves
Solvent	Solvent in which the solid dissolves
Solution	Mixture of a solute and a solvent
Soluble (adj)	Solid that dissolves
Insoluble	Solid that does not dissolve
Filtrate	Solution that passes through the filter paper on filtration
Residue	The insoluble solid collected on top of the filter paper after filtration
Miscible	Liquids that dissolve into one another
Immiscible	Liquids that do not dissolve into one another

Table 6: Methods of Purification

Mixture	Technique
Separating a Mixture of 2 solids; out of which one dissolves is some solvent	Dissolving, Filtering & Evaporation
Separating a Mixture of an insoluble solid, suspended in a liquid	Centrifuging
Separating a Mixture of an insoluble solid, in a liquid	Decanting
Separating solvent/water from Mixture of a soluble solid in a solvent/water	Simple Distillation
Separating miscible liquids from a Mixture of 2 or more miscible liquids	Fractional Distillation
Separating immiscible liquids form a Mixture of 2 or more immiscible liquids	Separating Funnel
Separating a Mixture of 2 solids, out of which one sublimes	Sublimation
Separating a Mixture of 2 solids, out of which, one has magnetic properties	Magnet
Separating a Mixture of 2 or more solutes, dissolved in a solution	Paper Chromatography