The atmosphere is a gaseous solution. It consists of nitrogen, oxygen,
argon, carbon dioxide, water, methane, and some other minor components.
Solutions are homogeneous mixtures. The major component is called solvent, and the minor components are called solute. If both components in a solution are 50%, the term solute can be assigned to either component. When gas or solid material dissolve in a liquid, the gas or solid material is called the solute. When two liquids dissolve in each other, the major component is called the solvent and the minor component is called the solute
Many chemical reactions are carried out in solutions, and solutions are also closely related to our every day lives. The air we breathe, the liquids we drink, and the fluids in our body are all solutions. Furthermore, we are surrounded by solutions such as the air and waters (in rivers, lakes and oceans).
On topic of solutions, we include the following sections.
Solving problems of solution stoichiometry requies the concepts introduced in
stoichiometry, which also provides the basis
for the discussion on reactions.
At the molecular level, molecules and ions of a solute are completely
mixed with and interact with those of the solvent when a solute
dissolves in a solvent. This type of mixing is homogeneous because
no boundary is visible in the entire solution. In a mixture, differences
may exist between regions or parts of the whole system.
Material exists in three states: solid, liquid, and gas. Solutions
exist in all these states:
The maximum amount of a substance dissolved in a given volume of solvent
is called solubility. Often, the solubility in water is expressed
in gram/100 mL. For example, the solubilities of some common substances
are given in the
Table of Solubility, which is also
listed in the HandbookMenu as Solubility.
A solution reached the maximum solubility is called a saturated solution.
Often, another phase such as gas, liquid, or solid of the solute is present
and in contact with in the solution. In general, there is no net change
in the amount of solute dissolved, but the system is by no means static.
In fact, the solute is constantly being dissolved and deposited at equal rate.
Such a phenomenon is called equilibrium.
In case another phase is not present, a solution may be unsaturated or
supersaturated. Yes, due to what can be attributed to a kinetic factor,
a solution may stay supersaturated for a long time. When promoted by a
seed, a solution may start to precipitate quickly. Sodium acetate has
a very high solubility at say 270 K. In fact, it can dissolve in the
water of crystallization similar to melting. When cooled, such a solution
stay in a meta-stable state. When a seeding crystal is
present or started due to surface of another medium, the entire solution
will solidify. During the crystallization process, heat is evolved, and
the solution becomes warm. Thus, such a solution, when properly packaged,
has been used as hand warmer packs for skiers.
One useful classification of materials is polarity. Substances such as
H2, O2, N2, CH4, CCl4
etc are called non-polar compounds, whereas H2O,
NH3, CH3OH, NO, CO, HCl, H2S,
PH3 etc are called polar compounds.
Regarding solubility, a useful rule is
Electrolytes or ionic substances are soluble in water due to hydration.
Due to the strong polarity of the water molecule, the positive and negative
ions are pushed apart. In general, reasonable size ions are believed to
have six water molecules around them, but these water molecules readily
exchange with those in the medium.
There are many applications of this rule. On the small scale, personal
hygiene and household cleaning requires various types of cleaning agents.
As a challenge is the research and development of cleaning agents in
industry, where you can find jobs or hire experts to do the R&D.
Other factor such as temperature and pressure also affects the solubility
of a solvent. Thus, in specifying solubility, one should be aware of the
factors.
Properties of a solution are very different from those of pure forms of
its components. For example, only pure water freezes or solidifies at 273 K,
and boils at 373 K. Freezing point of the ocean water is lower. Would you
expect the boiling point of a salt solution to be lower? Actually,
it's higher!
In Canada, we use a solution of equal volumes of ethylene glycol and
water as the engine coolant, because such a solution will not freeze
until the temperature drops to really low. What is the proper mixture
to use? Are you using your antifreeze properly? Deicing of airplane
wings in the winter is also an interesting application of solutions,
so is the use of salt on icy road.
A quantitative study of the physical properties of solutions is usually
given in a course in thermodynamics, and we only mention some
of the applications here just to raise your awareness of the solution.
Types of Solutions
Solubility
Properties of Solutions
Confidence Building Problems