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Types of Mixtures
Both milk and soil are examples of heterogeneous mixtures because their composition is not uniform
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Solutions
Suppose a sugar cube is dropped into a glass of water
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Sugar is
described as “soluble in water
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What happens as sugar dissolves? The
lump gradually disappears as sugar molecules leave the surface of their crystals and mix with water molecules
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Such a mixture is called a
solution
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In a solution, atoms,
molecules, or ions are thoroughly mixed, resulting in a mixture that has the same composition and properties throughout
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The
dissolving medium in a solution is called the solvent, and the substance dissolved in a solution is called the solute
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In a solution, the dissolved solute
particles are so small that they cannot be seen
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The solute-particle dimensions are those of atoms, molecules, and ions—which range from
about 0
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Types of Solutions
Solutions may exist as gases, liquids, or solids
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Many alloys, a metal made by combining two or more metallic elements to give greater strength or
resistance to corrosion, such as brass (made from zinc and copper) and sterling silver (made from silver and copper), are
solid solutions in which the atoms of two or more metals are uniformly mixed
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Solute State
Gas
Gas
Liquid
Liquid

Solvent state
Gas
Liquid
Liquid
Solid

Example
Oxygen in nitrogen
Carbon dioxide in water
Alcohol in water
Mercury in silver and tin (dental amalgam)

Solid
Solid

Liquid
Solid

Sugar in water
Copper in nickel (MonelTM alloy)

Suspensions
If the particles in a solvent are so large that the settle out unless the mixture is constantly stirred or agitated, the mixture
is called a suspension
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If left undisturbed, the particles of soil collect on the
bottom of the jar
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Gravity pulls them to the bottom of the container
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The particles
in suspension can be separated from heterogeneous mixtures by passing the mixture through a filter
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Particles between 1 nm and 1000 nm in diameter may form colloids
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The particles in a colloid are small enough to be suspended throughout the solvent by the constant movement of the
surrounding molecules
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Tyndall Effect
Many colloids appear homogeneous because the individual particles cannot be seen
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You have probably noticed that a headlight beam is visible from the side on a foggy night
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The Tyndall effect is a property that can be used to distinguish between a solution and a colloid
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They are seen to move rapidly in a random motion, which is due to collisions of rapidly moving molecules
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Solutions
Homogeneous
Particle size: 0
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Solutes: Electrolytes versus Nonelectrolytes
Substances that dissolve in water are classified according to whether they yield molecules or ions in solution
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Molecules are a group of
atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a
chemical
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These solute ions are free to move, making it possible for an electric current to pass through the solution
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Sodium
chloride, NaCl, is an electrolyte, as is any soluble ionic compound
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By contrast, a solution containing neutral solute molecules does not conduct electric current because it does not contain
mobile charged particles
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Sugar is a nonelectrolyte
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For a current to pass through the light-bulb filament, the test solution
must provide a conducting path between the two electrodes
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Such solutions contain solutes that are
electrolytes
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If a solution is a poor conductor, the
light bulb does not glow at all
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