Solutions

Chapter 12

A solution is a mixture that appears to be a single

substance but is actually two substances distributed in

each other in a single phase. We often call a solution a homogeneous mixture.

Saltwater is a common solution. Salt is very soluble in water. If a substance will

not dissolve, it is considered insoluble. The salt is

dissolved so it is considered the solute and the water does

the dissolving so it is considered the solvent.

Actually, solutions do not have to be a solid dissolved in a liquid. Since there are three common phases of

matter, there are nine possible types of solutions.

• Air is a gas dissolved in a gas.

• Soft drinks are a gas dissolved in a liquid.

• Humid air is a liquid dissolved in a gas.

• Antifreeze is a liquid dissolved in a liquid.

• Saltwater is a solid dissolved in a liquid.

• Brass is a solid dissolved in a solid. Solid solutions are called alloys.

A pizza is a good example of a mixture. A mixture is a combination of two or more

substances that are not chemically combined. Because the substances are not chemically

combined, each substance retains its identity and can be physically separated back out of

the mixture.

If a mixture contains large particles dispersed in a liquid or a gas that will settle out, it is classified as a suspension. If the particles of a suspension are not stirred

constantly, they will settle out as in a snow globe. Particles of a suspension can also be filtered out. The particles are large enough to be caught in filters. Other examples of suspensions would be dirty water, dust

storms, and Italian dressing.

A colloid is a mixture that contains solid particles dispersed in a liquid or gas but they are small enough that they won’t settle out. Milk, mayonnaise, stick deodorant, and jello

are examples of colloids.

The particles in a colloid are very small but they are still large enough to scatter light. One

has noticed the way that fog scatters headlights. This is called the Tyndall Effect.

Colloidal particles cannot be filtered. They are small enough to pass through filters with the

fluid that supports them.

A substance that dissolves in water to give a solution that

conducts electricity is considered an electrolyte.

A substance that dissolves in water to give a solution that

does not conduct electricity is considered an nonelectrolyte.

One can hasten dissolving by crushing the solute, stirring the solvent, and heating the

system.

The solubility of an substance is usually expressed as the number of grams that will

dissolve in 100 ml of solvent at a given temperature. Since the amount of substance that

will dissolve changes with temperature, solubility is

usually expressed as a graph.

Solution equilibrium is reached when the opposing actions of solvation and recrystallization

occur at the same rate.

A solution that contains the maximum amount of solute for

those conditions is considered a saturated solution. A solution

that contains any less amount is considered unsaturated.

A supersaturated solution is a solution that contains more solute than a saturated one

would under those conditions.

If two liquids blend into one another, they are considered

miscible.

Changes of pressure have little effect on the dissolution of

gases and liquids into solids however pressure has a

decided effect on the solubility of a gas into a liquid.

Henry’s Law states that the solubility of a gas in a liquid is

directly proportional to the partial pressure of the gas on

the surface of the liquid.

Effervescence is the rapid escape of a gas from a liquid as

the pressure is relieved.

Decreases in temperature tends to decrease the solubility of a

solid in a liquid and increase the solubility of a gas in a liquid.

Solution Concentration

• Molarity = Moles of sample/ liters of solution

• Molality = Moles of sample/ kilogram of solvent