Classification of Matter

Before studying further some topics in chemistry it is very important to know the basic concepts in chemistry, the classification of matter.  Matter is classified according to physical state ( as a gas, liquid, and solid) and according to the composition (as an element, compound and mixture).


States of Matter

Matter can be in the form of solid, liquid and gas, and this is called the phases or states of matter. This three forms of matter can be distinguished from one another by determining the corresponding properties of each.

1.  Solid has definite shape and volume.  It is rigid.  The molecules in solid are very closed to each          other and have definite arrangement.  The molecules can vibrate slightly in their fixed position and      cannot be compressed.

2.  Liquid has definite volume but no definite shape.  It takes the shape of the container it occupies.        The molecules are quite distant from each other and can move rapidly allowing each to slide one        another, that is why it can be poured. Liquids are not compressible.

3. Gas has no definite shape and volume.  It conforms to the volume and shape of the container.  The     molecules are far apart form each other and can move freely.  Gases are compressible.

Classification based from the Composition

Matter can be classified as pure substance and mixture.  Pure substance is a matter that has distinct properties and definite composition and does not vary from sample to sample.  Example is water, water has definite composition of hydrogen and oxygen.  Mixture, on the other hand, is composed of two or more substances that are combined.  It does not have definite composition.  Example of this is seawater, seawater is composed of two substances the water and salt.  Seawater has no definite composition of water and salt.  The components of mixture can be separated by physical means.


Pure Substance

Pure substances are classified into two classification, the elements and compounds. Element is the simplest form of matter.  It is only composed of only one kind of atom.  Since simplest form of matter, it cannot be decomposed into simpler form.  Example of this are O, oxygen atom, C carbon atom and N, nitrogen atom.  See more examples in the table below.

Some Common Elements  and their Symbols

Element                   Symbol
Flourine                         F
Chlorine                        Cl
Hydrogen                      H
Iodine                            I
Nitrogen                        N
Oxygen                         O
Sulfur                            S
Phosphorus                   P
Helium                          He
Aluminum                     Al
Barium                          Ba
Calcium                        Ca
Copper                          Cu
Magnesium                   Mg
Manganese                    Mn
Mercury                        Hg
Platinum                       Pt
Iron                               Fe
Lead                              Pb    

Note: You can refer to the Periodic Table of Element for complete list of all the elements.

Compound is composed of two or more elements chemically combined.  It has a definite composition and can be separated by chemical means.  Example of this is pure water, it is consist of 11% hydrogen and 89% oxygen by mass.  No matter how much amount of water we have, it still has the same composition.  This fixed composition of compounds is called Law of Definite Proportion (or Law of Constant Composition) formulated by the French chemist Joseph Louis Proust (1754-1826).  Compound also has fixed properties, water boils always at 100^oC, and freezes at 0^oC.

Examples of Compounds

Compound                  Formula
Water                                H₂O
Sodium chloride              NaCl
Carbon dioxide                CO₂
Carbon monoxide            CO
Ammonia                         NH₃
Magnesium chloride        MgCl₂
Potassium oxide               K₂O
Sulfur dioxide                  SO₂
Sulfur trioxide                  SO₃
Carbon tetrachloride        CCl₄
Iron (II) oxide                  FeO
Iron (III) oxide                 Fe₂O₃


Mixture

Mixture is composed of two or more substances.  The composition may vary from sample to sample. Each substance in a mixture retains its own identity and hence its own properties.  Mixture can be homogeneous and heterogeneous.  Homogeneous mixture is a mixture containing only one phase, meaning has uniform appearance while heterogeneous mixture containing two or more phases.  You can distinguish the components of heterogeneous mixture.  Example:  seawater (composed of salt and water) is a homogeneous mixture while sand in water is an example of heterogeneous mixture.  In seawater you cannot see the salt since it is being dissolve in water, while in sand in water, sand and water can still be seen and can be identified.


Types of Mixtures

Mixtures have three types; these are the solution, colloid, and suspension.  Solution is considered homogeneous mixture while colloids and suspension are heterogeneous mixture.  The three mixtures differ in their particles size.

1. Solution has the smallest particle size, that is why the particles are dissolved in the solvent.  The components cannot be separated by filtration, the particles will just flow together with the solvent. Example:  sugar in water, salt in water, alcohol in water, vinegar (acetic acid in water)

2. Colloid has intermediate particles size, enough to scatter light which is called the tyndall effect.  It may appear homogeneous to the naked eye but it is a heterogeneous mixture. The particles are suspended in the medium that is why it can scatter light. Example:  milk, cooked cassava starch in water, mayonnaise

3. Suspension has larger particles size.  The particles settle down at the bottom of the container after sometime. It can easily be separated by ordinary physical means like decantation and filtration.
Example:  sand in water, raw starch in water, clay in water


Methods of Separating Mixtures

Mixtures can be separated by ordinary physical means.  Mixtures can be separated differently.  Proper methods should be used in separating a particular type of mixture.  Knowing the kind of mixture and their corresponding properties will help you in determining the type of method to use to separate the mixture.

1.  Filtration is a method used to separate larger particle size mixture.  Filter paper is used in the laboratory attached to the funnel.  This method is best to use in suspension mixtures.

2.  Decantation is a method in which the particles are allowed to settle at the bottom for a few minutes and transferring the liquid to a different container.

3.  Distillation is a method in which a homogeneous mixture is heated allowing the liquid to vaporize.  The vapor is allowed to pass through a condenser, converting vapor back to liquid, and collected in  a receiving container.   Example, recovering pure water in seawater.

4.  Evaporation is another method of separating a homogeneous mixture.  This is when the solid particle is the needed by-product. The mixture is heated using evaporating dish, allowing volatile components to evaporate leaving the desired component on the container.  Example, recovering salt in seawater.

5.  Chromatography is another method of separating colored mixtures like, dyes, ink, and coloring agents in food.  This is done in a piece of paper in which a spot of the mixture is placed in a paper and is allowed to stand upright the solvent.  As the solvent travels on the paper the components are carried by the solvent with different rates depending on the difference of their masses.