solutions chapter 12. a solution is a mixture that appears to be a single substance but is actually...
TRANSCRIPT
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.
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.
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.
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