Chapter 13 Flashcards
How a solution is formed
- When one substance disperses uniformly throughout another
- When the magnitudes of the attractive forces between solute and solvent particles are comparable to or greater than those that exist between the solute particles themselves or between the solvent particles themselves.
Ability of substance to form solutions depends on 2 general factors
1) the types and relative strengths of intermolecular interactions between and among solute and solvent particles
2) natural tendency of substances to spread into larger volumes when not restrained
Ion-dipole forces dominate (when?)
Solutions consist of ionic substances in water
Dispersion forces dominate (when?)
Nonpolar substance dissolves in another nonpolar one.
How to identify a solvent
Normally the component present in the greatest amount
How to identify a solute
Other components in a solution other than the solvent (which is ththe greatest quantity)
Gas + Gas =
Gas
Liquid + Gas =
Liquid
Liquid + Liquid =
Liquid
Liquid + Solid =
Liquid
Solid + Gas =
Solid
Solid + Liquid =
Solid
Solid + Solid =
Solid
Entropy
The degree of randomness in a system (disorder).
Crystallization
When a solution reforms into solvent; when particles of solute reattach to a solid.
Saturation
A solution in equilibrium with undissolved solute
Solubility
The amount of solute needed to form a saturated solution in a given quantity of solvent, at a specified temperature.
Unsaturated solution
Less solute is dissolved than that needed to form a saturated solution
Supersaturation
Solutions with more solute than that needed to form a saturated solution (unstable condition).
Effect of increasing molecular mass or polarity on solubility
Solubility increases with increasing molecular mass or polarity
The stronger the attractions are between solute and solvent molecules, the greater/lesser the solubility
Greater
Polar liquids tend to dissolve readily in polar solvents because
of favorable dipole-dipole attractions between solvent molecules and solute molecules.
Miscible
Pairs of liquids that mix in all proportions
Immiscible
Liquids that do not dissolve in one another
Nonpolar liquids tend to be insoluble in polar liquids because
the attraction between the polar water molecules and the nonpolar hydrocarbon molecules is not sufficiently strong to allow the formation of a solution.
What does “like dissolves like” mean?
Substances with similar intermolecular attractive forces tend to be soluble in one another.
Solubilities of solids and liquids are/are not appreciably affected by pressure
Are not
Solubility of gases are/are not appreciably affected by pressure
Are
Effect of pressure on solubility of gas
Solubility of the gas increases in direct proportion to its partial pressure above the solution
Henry’s law
Sg = kPg Sg = solubility of the gas in the solution phase (expressed as molarity) Pg = partial pressure of the gas over the solution k = proportionality constant called Henry's law constant
what is Henry’s law constant?
Different for each solute-solvent pair
Varies with temperature
Effect of temperature on solubility of solids
The solubility of most solid solutes in water increases as the temp increases
Effect of temperature on solubility of gases
Solubility of gases in water decreases with increasing temp
Mass % formula
g solute/g solution * 100
Also, g solute/(g solute + g solvent)
Mole fraction
mol solute/mol solution
Also, mol solute/(mol solute + mol solvent)
-Moles of component/total moles of all components
Molarity (M)
mol solute/L solution
Molality (m)
mol solute/kg solvent
How to convert m (molality) to mole fraction
convert kg of solvent to mol of solvent and use the above formula
What is the conversion factor between molarity and molality?
density of the solution (g/L)
Colligative propertios
Boiling point, freezing point, vapor pressure (skipping calculations for test), osmotic pressure
Normal boiling point
Temp at which a liquid’s vapor pressure will equal 1 atm
Boiling point elevation equation
Delta-Tb = Kb x Cm (or, Kb x m)
(change in temp = molal bpe constant, times the molality of the solution)
Also, Delta-Tb = Tb solution - Tb solvent
Freezing point depression equation
Delta-Tf = Kf x Cm (or, Kb x m)
(change in temp = molal fpd constant, times the molality of the solute)
Also, Delta-Tb = Tb solvent - Tb solution
Osmotic Pressure (definition)
Pressure difference at equilibrium; the applied pressure required to prevent the net movement of water from solute to solution (prevent osmosis by pure solvent)
Osmotic Pressure equation
II = MRT
Molarity, times the ideal-gas constant, times temp (K)
