SOLUTIONS
Solutions are a homogeneous mixture of 2 or more substances that is uniform throughout.
1. Solvent- the substance that is present in the largest amount and has another substance
dissolved in it.
2. Solute- a substance that is present in the smaller amount and is dissolved in a solvent
Note: Table is from The McGraw-Hill Companies, Inc. Properties of Solutions Powerpoint.
A chemical reaction does not take place for a solute to dissolve in a solvent. We know this
because the intermolecular forces are what attract solvents and solutes and also solutions can be
physically separated from one another (ex: distillation, filtering, etc.) Remember that not all
solutions are liquids, they are also in the form of a gas or a solid. (see table 7.1 in textbook)
Liquid Solutions:
Aqueous solution- an aqueous solution has water as the solvent
Miscible liquids- can be combined in any proportions. Alcohol and water are soluble in one
another in any proportion. In a solution of alcohol and water, either liquid could be the solvent
depending on what is present in the greater amount.
Immiscible liquid- liquids that do not dissolve in one another (oil and water)
Solubility and Saturation:
Solubility- the mass of solute that dissolves in a given quantity of solvent at a certain
temperature. (Ex: 36g of NaCl can dissolve in 100mL of water at 20۫C
Molar solubility- the amount in moles of dissolved solute in 1L solution
Saturated solution- a solution in which no more solute will dissolve in a given amount of solvent
at that temperature.
Unsaturated solution- a solution in which more solute can still dissolve
Super saturation solution - a solution containing more solute than is present in a saturated
solution at a specific temperature. (A hot solution cooled very slowly so that excess solute will
not precipitate.)
Example: Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated
solution of sodium acetate.
Note: Image from The McGraw-Hill Companies, Inc. Properties of Solutions Powerpoint.
What about solutes that “kind of” dissolve in solvents?
When we say a solute is soluble, this generally means that the solubility is greater than
1g/100mL of solvent. Those that have a solubility less than 0.1g/100mL are considered
insoluble. Slightly soluble substances are those that fall between 0.1-1g/100mL.
Intermolecular forces:
Dipole-Dipole interactions: the attraction between opposite charges on 2 different polar
molecules. This is only 1% as strong as ionic or covalent bonds.
Hydrogen bonding- dipole-dipole attractions when hydrogen is bonded to a very
electronegative atom such as O, F, or N. This is stronger than dipole-dipole. Water is an
example of a molecule that has hydrogen bonding.
Ion-dipole- opposite charged ends of an ionic compound and polar molecule attract. Ion-dipole
attraction must be greater than the bond within the ionic compound.
(See dissociation/ion-dipole attraction animation)
Dispersion (London) forces- a force between all molecules, however it is especially important
for non-polar molecules and how they interact. Non-polar molecules can have a momentary
distribution of charge to become polar and induces another polar molecule. The size of the
molecule affects the strength of the force. Larger objects have a stronger dispersion force.
Compound Lewis or
Structural
Diagram
C2H2
NBr3
CH3F
CH2O
Shape
Name
Shape
Diagram
Polarity
(P/NP)
Min. 1 polar
bond, and
asymmetrical
shape
Types of
Intermolecular
Force
(Dispersion,
Dipole-dipole,
Hydrogen
bonding)