Solutions

A solution is a homogeneous mixture of two or more substances at the molecular or ionic level.
Formation of a solution is a physical change where a single phase exists. Individual molecules or ions exist within the solution.
Components of a true solution cannot be separated by filtration, settling, or centrifugation.
A solute may change its physical state, but the solvent retains its physical state.
Solutions can be binary, ternary, quaternary, etc., based on the number of components.
A binary solution has only two components: solute and solvent.
$Solute + Solvent = Solution$
The substance in a smaller proportion in a binary solution is the solute. It's the dissolved or dispersed component.
The substance in a larger proportion is the solvent, also known as the dissolving or dispersion medium.
In solid-liquid solutions, the solid is the solute, and the liquid is the solvent, regardless of their amounts.
Based on the physical state, solutions are of 3 types:
- Gaseous solutions: Gas is the solvent.
- Liquid solutions: Liquid is the solvent.
- Solid solutions: Solid is the solvent.
In any type of solution, the solute may be a gas, liquid, or solid.
Solutions are classified into 7 types based on the physical states of solute and solvent:
1. Gas in gas: Mixture of any two gases.
2. Gas in liquid: Soda water.
3. Liquid in liquid: Alcohol in water.
4. Solid in liquid: Sugar in water.
5. Gas in solid: $H_2$ occluded in Pd.
6. Liquid in solid: Amalgams.
7. Solid in solid: Alloys.
Liquid in gas and solid in gas mixtures are not considered true solutions because they are not homogeneous.
An aqueous solution uses water as the solvent.
An alcoholic solution uses alcohol as the solvent.
A non-aqueous solution uses an organic liquid as the solvent. Common non-aqueous solvents include $CCl4$ , $CS2$ , $CHCl3$ , $C6H6$ , liquid $SO2$ , acetic acid, and liquid $NH_3$ .
Based on the amount of dissolved solute, solutions are classified into 3 types:
- Saturated solutions: Cannot dissolve any more solute; some undissolved solute is present, and a dynamic equilibrium exists between dissolved and undissolved solute.
- Unsaturated solutions: Can dissolve more solute; no excess undissolved solute exists, and there is no dynamic equilibrium.
- Super-saturated solutions: Contain excess dissolved solute, are unstable, and have no equilibrium.
Concentration: The quantity of the solute in a definite quantity of the solution relative to the solvent is the concentration or strength of the solution.
A solution with a known concentration is called a standard solution, prepared in a standard flask.
A dilute solution contains less solute than the solvent, having a very low strength.
A concentrated solution contains excess solute in a definite quantity of the solution, having a very high strength.
Weight of the solution = Volume of the solution × density of the solution
$W = V imes d$
The weight of one milliliter of a solution in grams is the density of the solution, which depends on the temperature. Units are grams/ml.
Relative density (or specific gravity) is the ratio between the density of the solution and the density of water at the same temperature. Specific gravity has no units.
Various terms used in concentration:
- Weight percent: $Weight fraction = ext{weight of solute} / ext{weight of solution}$
  $Weight percent = ( ext{weight of solute} / ext{weight of solution}) imes 100$
- Volume percent: $Volume fraction = ext{volume of solute} / ext{volume of solution}$
  $Volume percent = ( ext{volume of solute} / ext{volume of solution}) imes 100$
Volume percent is applicable for solutions containing both solute and solvent as liquids.
Solubility: The weight of solute dissolved in 100 grams of solvent to form a saturated solution.
$Solubility = ( ext{weight of solute} / ext{weight of solvent}) imes 100$
Molarity (M): The number of gram moles of the dissolved solute per liter of solution.