Chapter 8
Solutions
Water is perhaps the most important compound on our planet
Water has several very important properties
Surface tension*
Adhesion/Cohesion*
Freezing/Boiling*
*All three are caused by hydrogen bonds
Water is an excellent solvent!
Hydrogen bonds
Attractions between a hydrogen on one water molecule and an oxygen on another
water molecule
Solutions
Solutions form when one substance dissolves into another
Most solutions are water solutions
All solutions have two parts
Solvent: The dissolving medium (water is the most common solvent),
usually more than 50% of the solution
Solute: The substance which actually dissolves (e.g. salt, sugar, etc.),
usually less than 50% of the solution
Electrolytes - solutes that form ions (charged particles) in solution
NaCl (s) + H2O(l) --> Na+(aq) + Cl-(aq)
CaCl2(s) + H2O(l) --> Ca+2(aq) + 2Cl-(aq)
Notice the mole ratio (# of particles in solution)
Nonelectrolytes – solutes that do NOT form ions in solution; instead they form
uncharged particles (molecules) in solution.
C12H22O11(s) + H2O(l) --> C12H22O11(aq)
Compare the # of particles in solution to an electrolyte.
The Effect of Particle Polarity on Solubility
Water is a polar molecule
Polar molecules and ions can be effectively hydrated by the water molecules
Solutes which are nonpolar are not effectively hydrated by water but can be
effectively dissolved by nonpolar solvents.
Examples
Vitamins
Water Soluble - C and B
Fat Soluble - A, D, E, K
Types of solutions
Unsaturated: contain less than the maximum amount of solute
Saturated: contain the maximum amount of solute
Supersaturated: contain more than the maximum amount of solute
Solubility Rules
There are some general rules for the solubility of ionic compounds (SALTS) in
water, allowing you to predict the outcome of chemical reactions that occur in
aqueous environments.
Soluble - the salt is readily soluble in water
Insoluble - the salt dissolves to such a tiny extent that it is not possible to
detect it with the naked eye
Identifying Precipitates in Reactions Where a Solid Forms
AgNO3(aq) + KCl(aq) --> white solid
KNO3(aq) + BaCl2(aq) --> NR
Na2SO4(aq) + Pb(NO3)2 --> white solid
KOH(aq) + Fe(NO3)3(aq) --> white solid
Examples of Writing DR equations
AgNO3(aq) + AlCl3(aq) -->
K2SO4(aq) + BaCl2(aq) -->
Na2SO4(aq) + Pb(NO3)2 -->
KOH(aq) + Fe(NO3)3(aq) -->
Factors Affecting Solubility
Solubility can be increased by
AGITATION
SURFACE AREA OF SOLUTE
Block vs. powder
TEMPERATURE
Increase temperature for solid solutes (generally)
Decrease temperature for gaseous solutes
PRESSURE (affects gaseous solutes)
Solubility
Concentrated vs. Dilute Solutions
Measurement of solution concentration
Percent of solution
m-m
v-v
m-v
Moles of solute per volume of solution
Molarity (M) = mol solute/liters soln
Molarity Examples
Determine the molarity of a solution made by dissolving 1.5 mol NaCl in enough
water to make 0.45 liters.
Determine the molarity of a solution made by dissolving 12.5 grams of sodium
hydroxide in 555 mL solution.
How many grams of KCl are needed to make 2.5 liters of a 0.50 M solution?
Explain how to make 0.500 L of 3.5 M NaOH.
What is the molarity of a solution made by dissolving 13.7 g AlCl3 in water to
make 275 mL solution?
How many grams of KMnO4 are required to prepare 600.0 mL of 0.25 M
KMnO4?
What volume of 0.075 M Ca(NO3)2 can be prepared with 10.4 g of the solute?
What is the molarity of 4.5 L solution containing 14.3 moles of sodium chloride?
How many liters of a 0.25 M KOH solution can be made using 1.55 moles of
solute?
How many moles of Mg(NO3)2 are needed prepare 10.0 L of a 2.00 M solution?
Dilutions
When you add solvent to dilute a solution you do NOT change the amount of
moles of solute
molesbefore = molesafter
M1V1 = M2V2
this is very useful in the lab
Examples
How much 12.0 M HCl is needed to prepare 250.0 mL of 2.5 M HCl?
How would you prepare 67.5 mL of 0.25 M K2CrO4 using 6.0 M K2CrO4?
Solution Stoichiometry
Balanced equations can be used to predict the outcomes of reactions occurring in
solution
EX. 50.0 mL of 1.5 M HCl reacts completely with 100.0 mL of 0.075 M NaOH.
How much NaCl can be formed?
EX. Barium chloride solution reacts with sodium sulfate solution.
What mass of barium chloride do you need to prepare 10.0 mL of 0.05 M BaCl2?
What is the stoichiometric equivalent (in grams) of sodium sulfate?
Colligative Properties
Dissolved particles effect certain properties of solutions
These properties are affected by the AMOUNT of solute particles
Concentration
Electrolytic nature of solute
Particle Effects
Colligative Properties
Freezing Point Depression
Boiling Point Elevation
Osmotic Pressure
Osmosis
Type of Solution
Reverse Osmosis
Dialysis: Impurities can be removed from a colloidal dispersion by using a dialysis
procedure.