Section 2.3

Classifying Matter

1. To learn to distinguish between mixtures and pure substances.

2. To identify homogeneous and heterogeneous mixtures.

Objectives

Question:

Does matter most commonly occur as pure substances or mixtures?

Section 2.3

Classifying Matter

A. Mixtures and Pure Substances

• Matter can be classified as a mixture or a pure substance.

Section 2.3

Classifying Matter

A. Mixtures and Pure Substances

Mixtures

• Combination of 2 or more pure substances (elements and compounds)

Examples: wood, gasoline, soil, air

• Variable composition –the proportions of the components of the mixture can vary

Examples: Milk – whole, 1 %, 2 %, skim, lowfat, etc.

Section 2.3

Classifying Matter

Mixtures

• Can be separated into individual pure substances by physical methods.

Mixtures

Homogeneous Heterogeneous

Homogeneous – visibly indistinguishable parts (a solution)

Heterogeneous – visibly distinguishable parts

Section 2.3

Classifying Matter

Mixtures

Examples of Homogeneous Mixtures:• Air – solution of gases (nitrogen, oxygen, carbon dioxide,

helium, argon, etc.)• Wine – solution of liquids (water, ethanol, etc.)• Brass – solution of metals (copper and zinc)• Saltwater – water and salts

Examples of Heterogeneous Mixtures• Sand and water• Sedimentary rock

Section 2.3

Classifying Matter

A. Mixtures and Pure Substances

Pure Substances

• A pure substance always has the same composition. • Pure substances are of two types:

– Elements which cannot be broken down chemically into simpler substances

– Compounds which can be chemically broken down into elements

Water is a compound. All thecomponents are the same—H2O molecules.

Section 2.3

Classifying Matter

Separation of Mixtures

• Mixtures can be separated into pure substances by various means.

• Separations are based on differences in physical properties

• magnetism• mass• solubility• states of matter• boiling point• size

Section 2.3

Classifying Matter

B. Separation of Mixtures

• distillation

•Can be used to separate homogeneous liquid mixtures•Mixtures are separated because parts of the mixture have different boiling points

Section 2.3

Classifying Matter

B. Separation of Mixtures

• filtration

•Can be used to separate heterogeneous solid, liquid, and gas mixtures•Used to separate solids from mixtures

Section 2.3

Classifying Matter

Separation of a Mixture

Crystallization 

Description: A liquid solution is heated until the liquid boils. Solids are left behind.

For example, a saltwater solution can be separated by heating the solution in a beaker on a hotplate. The water evaporates and solid salt is left behind on the beaker.

 • Used to separate homogeneous or heterogeneous liquid

mixtures.• Parts of a mixture are separated because they have

different boiling points

Section 2.3

Classifying Matter

Separation of a mixture

Chromatography

 

Description: Many types of mixtures can be separated by passing the mixture through a porous substance.

 

For example, the ink pigments that are mixed together to make black ink can be separated by spotting the ink on a piece of filter paper and inserting the paper into a beaker of water.

• Mixtures are separated because the parts of a mixture move at different speeds through a porous substance.

Section 2.3

Classifying Matter

Summary: The Organization of Matter