section 2.3 classifying matter 1.to learn to distinguish between mixtures and pure substances. 2.to...

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