Post on 20-Jan-2016
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