Solutions
All solutions are homogeneous mixtures made up of very small particles like
molecules and atoms. No matter how long the solution will stand, the particles
will never settle out. If a beam of light was shined through it, the beam would
not be seen since the particles are so small. Also due to small size of the
particles, a solution can pass right through the finest filters. Most of the time a
solution consists of a mixture of two substances, so the substance that is being
dissolved then is called a solute and the substance in which the solute is
dissolved is called a solvent.
Types of solutions
1.) Gas solutions - A gas solution can be a gas dissolved in a gas, or a liquid
dissolved in a gas, or a solid dissolved in a gas. The one thing that they all
have in common is that they end up in the gaseous phase. The air that we
breathe would be an example of a gas solution. It has gases dissolved in each
other and it also has a liquid (water) dissolved in a gas.
2.) Liquid solutions - A liquid solution can be a solid dissolved in a liquid, or a
liquid dissolved in a liquid, or a gas dissolved in a liquid. They all end up in
the liquid phase and this is what classifies them as liquid solution. Liquid
solutions are the most common types of solutions since they include all water
solutions (aqueous). Examples of liquid solutions would be; saltwater (solid in
liquid), soda pop (gas in liquid), or liquor (liquid in liquid).
3.) Solid solutions - A solid solution can be a solid dissolved in a solid, or a
liquid dissolved in a solid, or a gas dissolved in a solid. In all three cases, the
solutions end up in the solid phase and are therefore classified as solid
solutions.
Factors that affect the rate of solution
1) Size of the particles - Breaking a solute into smaller pieces increases its
surface area and hence its rate of solution.
2) Stirring - stirring brings more fresh solvent in contact with the solute, so the
process is sped up.
3) Amount of solute already dissolved - if there is a lot of solute already
dissolved, it is harder for the solute particles to come in contact with fresh
solvent particles and the rate of solution decreases.
4) Temperature - by heating up a solution, particles begin to move more
rapidly and they come in contact more, so this speeds up rate of solution
(except for gases).
Solubility
The solubility of a substance is the amount of solute that will dissolve in a
specific amount of solvent at a specified temperature. The solubility of a
substance is commonly listed in the units of grams/liter at 25 °C and 1 atm.
The temperature and pressure are specified because solubility can be affected
by temperature and pressure.
Factors Affecting Solubility
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Temperature - Higher temperatures for most solids and liquids increase
their solubility and you can get more to dissolve. Gases become less
soluble at higher temperatures.
Pressure - Gases become more soluble as the pressure on them
increases. Pressure changes have very little effect on the solubility of
liquids and solids.
Nature of the solvent and solute - Polar substances tend to dissolve
polar and ionic substances while nonpolar substances usually dissolve
nonpolar substances. The polarity of the solvent and solute will
determine how soluble they are in each other.
Solutions that are holding the maximum amount of solute possible at a given
temperature are said to be saturated. If a solution has been stirred and there is
still solid settling to the bottle of the container, the solution is saturated and the
solute that could not dissolve will settle to the bottom. A solution that can still
hold more solute is said to be unsaturated. Under the right conditions it is
possible to have a solution that is supersaturated. A supersaturated solution is
one that has more solute dissolved than should be possible at a given
temperature. A supersaturated solution is usually made by heating a solution
up so that more solute will dissolve and then letting it cool down undisturbed
and sometimes the solute will stay dissolved.