Solution is a homogeneous mixture of 2 or more substances in a single state.
Solution Properties:
1. Comprised of small particles ( atoms, molecules, ions)
2. Particles are evenly distributed on a
molecular level
3. Particles don’t settle or separate from solution
Two Components:
Solute – substance dissolved (broken down)
Solvent – substance doing the dissolving
seawater:
solute – salt
solvent – water
Solutions Terms:
Soluble –
a substance dissolves in another substance
Salt and sugar are soluble in water
Insoluble –
a substance that does not dissolve in another
Mercury and oil are insoluble in water
Miscible –
Liquids soluble in each other at all proportions
Water and ethanol are miscible
Alloys – Solid solutions of metals
Bronze = ( Cu + Sn + Zn )
Gold Jewelry = ( Au + Cu)
Types of Solutions:
Solute
Solvent
Example
Gas
Gas
Air ( O2 in N2)
Gas
Liquid
Soda ( CO2 in H2O )
Liquid
Liquid
Antifreeze
Solid
Liquid
Ocean water (salt in H2O)
Gas
Solid
Charcoal filter
( gas in carbon )
Liquid
Solid
Dental Filling
( Hg in Ag )
Solid
Solid
Sterling Silver
( Cu in Ag )
(ethylene glycol in water)
Mixture Types: Solution, Suspension, Colloid
Suspensions
Heterogeneous mixture of a solvent – like substance, particles slowly settle
out; ( Soil + Water); Scatters Light = “Tyndall Effect”
Colloids / Colloidal Dispersions
Mixture with particle size between solutions and suspensions
(Muddy water, inks, Foams, Fog, Smoke, liquid - liquid emulsion)
Classify the following:
 Sand + water mixture = Suspension
 Brass door knob
= Solution ( alloy)
 Atmospheric Cloud = Colloidal dispersion
Aqueous Solutions – Solutions with water as the solvent
Water called the “ Universal Solvent “ It can dissolve so many substances
2 types of substances dissolve in water
1. Electrolytes
2. Non-electrolytes
Electrolytes – ionic compounds dissolved in water that yield ions.
Mobile ions in solution carry electrons (current) NaCl is an electrolyte
Nonelectrolyte – substance dissolved in water that does not conduct
electricity
No mobile ions
Sugar is a nonelectrolyte or neutral solute
Solution Formation
1. Dissolving occurs at solid surface
2. Water molecules separate or dissociate the NaCl into ions
3. Water molecules surround the ions
Dissociation:
NaCl(s) + H2O(l) → Na + (aq) + Cl – (aq)
Solvation – Solvent – Solute interaction
Hydration – Water – Solute interaction
Heat of Solution
NaCl solution formation breaks attractions among solute particles
Energy absorbed to separate solute particles
Endothermic Process;
Solution Temperature decreases
NH4NO3(s) + H2O(l) + Heat → NH4+(aq) + NO3 –(aq)
“Cold Pack” reaction
Formation of attractions between solute – solvent particles
Energy released ;
Exothermic process
Solution Temperature increases
NaOH(s) + H2O(l) → Na+(aq) + OH –(aq) + Heat
Solubility
Amount of solute dissolved in a specific solvent under given conditions
Units: grams of solute per 100 grams of solvent at a specific temperature and
pressure
g solute / 100 g solvent at ( T, P )
Factors affecting solubility:
1. Nature of solute and solvent
2. Temperature
3. Pressure for gases
Polar vs. NonPolar Nature of solvent
Polar molecules have polar bonds
Charge separation due to electronegativity difference
Water is a Polar molecule
Nonpolar Molecules have:
o Nonpolar bonds with comparable electronegativites
o No net Dipole Moment
Polar substances
Water
Alcohols
Acids
Acetone
Ionic Compounds
NonPolar substances
Hydrocarbons (Benzene)
Carbon tetrachloride (CCl4)
Chloroform (CHCl3)
Oils, Waxes, Greases
Gasoline
“ Like dissolves Like” Rule
Two substances dissolve in each other if their molecules are alike in polarity
Water + Grease
=
(Polar) + (NonPolar) =
Turpentine + Grease
=
(Nonpolar) + (Nonploar) =
Insoluble
Insoluble
Soluble
Soluble
Like dissolves Like
Solute
Polar Solvent
Nonpolar Solvent
Polar
Soluble
Insoluble
NonPolar
Insoluble
Soluble
Ionic
Soluble
Insoluble
Affect of Pressure on Gas Solubility
Solid & Liquid solubility not affected by pressure
Increase in Pressure = Increase in Gas Solubility
(over a solvent)
(in any solvent)
Increase in pressure = increase in gas molecule’s strike rate at solvent surface
to enter the solution
Pressurized liquid has more gas dissolved in it
Closed soda bottle Pressure > 1 atm;
Increase solubility of CO2
Henry’s Law
Gas solubility increases with the partial pressure of that gas on the liquid
surface at a constant temperature.
Factors Affecting Dissolving Rate :
1.
2.
3.
Surface Area
Temperature
Stirring
Increase surface area by decreasing particle size
Compare two solids of equal masses,
Fine Powder
(Large surface Area)
(small particle size)
vs.
Large granules
(small surface area)
(large particle size)
Increase surface area = increased dissolving rate
Increase stirring = increase dissolving rate
 Solvation occurs at solid surface
 Stirring provides fresh solvent at solute surface
Higher Temperature = Increase Solvent Kinetic energy
 Increase # of solvent particles in contact with solute
 Increase Temperature = faster dissolving rate
Types of Solutions:
Saturation
Saturated solution contains a maximum amount of solute as can be dissolved
under existing conditions
Saturation not the same as concentration
Unsaturated solution contains less than the maximum amount of solute than
can be dissolved
Supersaturated solution contains a greater amount of solute than that
needed to form a saturated solution
Supersaturated solutions are very unstable, solute crystallizes out of solution
Examples: Rock Candy, Sodium Acetate
Solution Concentration
Amount of solute in a given amount of solvent or solution
Concentrated solution – a large amount of solute in the solvent
Dilute solution – a small amount of solute in the solvent
Units of Solution Concentration:



Percent by mass
Molarity
Molality
Percent by Mass
Number of solute grams dissolved in 100 g of solution.
% by Mass = __Solute Mass______ __ x 100
Mass solute + Mass solvent
10 g of sodium hydroxide is dissolved in 90 g H20
% mass of solute = 10 g NaOH_______ x 100
10 g NaOH + 90 g H2O
(10 g / 100 g ) x 100
= 10 % solute by mass
A solution of sodium chloride prepared by dissolving 5 g of salt in 550 g water.
% solute by mass = ?
5 g NaCl / (5 g NaCl + 550 g H2O) x 100 = 0.9% NaCl
Molarity ( M )
Number of moles of solute in one liter of solution
Molarity = moles solute
Liter solution
M = n/V
1 molar solution of HCl contains one mole of HCl in every liter of solution.
( 1 M HCl)
10.0 g NaOH dissolved in solvent to make a 0.100 L solution.
What is the molarity of the solution?
Molality (m)
Solute moles per kilogram of solvent
Molality = moles solute
mass solvent (kg)
1 kg = 1,000 g
1 molal solution contains 1 mol solute in exactly 1 kg of solvent
35.0 g ammonia (NH3) dissolved in 1 Kg water. Molality of solution =?
35.0 g NH3 = 2 mol
Molality = 2 mol NH3 = 2 m NH3
1 kg H2O
Colligative Properties of Solutions
 Vapor-Pressure Lowering
 Boiling-Point Elevation
 Freezing-Point Depression
Colligative properties depend on the
# solute particles, not their chemical nature
Vapor Pressure reduction occurs as nonvolatile solute prevents solvent
particles from escaping at the surface.
Boiling - Point Elevation:
At BP, VPeq = AP
Therefore, decrease VP = Increase BP