Unit B-Chapter 2-Lesson 2

How Do Solutions Form?

Forming Solutions

• A solution is a mixture in which the particles of different substances are evenly distributed and are too small to see with the naked eye.
• A solution appears as a single substance.
• The formation of a solution is a physical change.
• The substances that make up the solution retain many of their original properties.

Example:

• When sugar is dissolved in water, its sweet taste remains.

A solvent is a substance that dissolves other materials

A solute is a substance that is dissolved.

Example:

• In a solution of Kool-Aid, the water is the solvent and the sugar flavoring powder is the solute.

All solutions have solvents and solutes.

Types of Solutions

Some common examples of solutions are:

• perfumes
• cooking extracts
• gasoline
• air
• sterling silver
• tooth fillings
• carbonated beverages (such as soda)

• In a solution, the solvent or solute can be solid, a liquid, or a gas.
• Metal alloys are solutions of solids in solids.
• The metals are melted and mixed, and when they harden, the resulting substance looks uniform.
• These alloys are useful because they combine the properties of different metals.

Examples:

Carbonated beverage = carbon dioxide (solute) + water (solvent)

Brass = copper (solute) + zinc (solvent)
Dental Fillings = mercury (solute) + silver (solvent)

A dilute solution describes a solution with a small amount of solute compared to the amount of solvent

Example:

• Kool-Aid with more water than flavoring.

A concentrated solution describes a solution with a large amount of solute compared to the amount of solvent.

Example:

• Kool-Aid with extra flavoring mixed with the water.

Dissolving Faster

• Because the solution process depends on contact between particles of the solvent and particles of the solute, any action that increases the number of collisions between the solvent and the solute particles tends to increase the rate of dissolving.
• Both stirring and heating the solution increase the rate of collisions.
• Breaking the solute into smaller pieces increases the rate of disolving by increasing the surface area of the solute,
• Icreased surface area allows more solvent particles to come in contact with more solute particles.
• Heating the solvent increases the speed of the solvent particles, and they collide with the solute with greater force, knocking particles away from the solute.
• The increased motion of the solvent particles acarries away more solute particles, leaving fresh surface areas exposed.
• Particles in a heated liquid are spaced farther apart, so there is more space between them for solute particles.
• In general, more solute dissolves in a solvent at higher temperatures than at lower temperatures.

Unit B-Chapter 2-Lesson 1

How Does Matter Change State?

States of Matter

Matter exists in three states:

• Solid
• Liquid
• Gas

A solid has a definite shape and definite volume
Example: Ice

A liquid has a definite volume, but no definite shape
Example: Water

A gas has no definite shape or volume.  It will occupy the volume of whatever container it is in.
Example:  Steam

• In a solid, particles of matter are very close together and are held together by the attraction of the particles for one another.
• When a solid, such as ice, is heated, its particles move faster and farther apart.  When the substance reaches its melting point, the solid changes to a liquid.
• Eventually the particles gain enough energy to escape.  When the particles reach this point, the substance becomes a gas.
• All three states of matter exist on earth.

Melting and Boiling

• Although most substances normally exist on Earth in just one state, all materials can exist as solids, liquids, or gases.

Example:
On the surface of Venus, which is very hot, lead would be a liquid rather than a solid as it is on Earth.

• The state of a substance depends on its temperature and the amount of attraction between its particles.
• The temperature at which a substance changes from a solid to a liquid state is called its melting point. 
• Melting occurs because particles gain heat.
• When the particles in a liquid lose energy, they move more slowly. 
• If the substance is cool enough, the particles slow down to the point where the liquid becomes a solid.
• The temperature at which a liquid changes to a solid is called its freezing point.
• In pure substances, melting and freezing occur at the same temperature.

Boiling and Evaporation

• If a liquid is heated enough, all the particles in the liquid eventually will have enough energy to break free at the surface. (The liquid changes to gas)
• The temperature at which this occurs is called the boiling point.
• Different substance have different boiling points.
• A substance can change from liquid to a gas through evaporation.
• Evaporation is the change in state from a liquid to a gas at the surface of a liquid.
• Evaporation can occur at any temperature because some of the particles at the surface always have sufficient energy to escape.
• However, evaporation takes place more quickly in hotter liquids.
• The change of state from a gas to a liquid is called condensation.