To learn to distinguish between mixtures and pure substances.

1
Objectives

1. To learn to distinguish between mixtures and pure
   substances.
2. To identify homogeneous and heterogeneous
   mixtures.

Question Does matter most commonly occur as pure
substances or mixtures?
2
A. Mixtures and Pure Substances

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

3
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.

4
Mixtures

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

Mixtures
Homogeneous
Heterogeneous
Homogeneous visibly indistinguishable parts (a
solution) Heterogeneous visibly distinguishable
parts
5
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

6
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

7
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

8
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

9
B. Separation of Mixtures

• filtration

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

10
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

11
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.

12

• Summary The Organization of Matter