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SOLUTIONS
Definitions
solvent – bulk material used to dissolve substance
solute – material dissolved in solvent
Examples
1) salt water
solvent – water
solute – salt
2) dish water
solvent – water
solute – dish soap
3) engine coolant
solvent – ethylene glycol
solute – water
Types of solutions
Gas in Gas
Gas in Liquid
Liquid in Liquid
Solid in Liquid
Solid in Solid
Oxygen in Nitrogen
Carbon dioxide in Water
Oil in Gasoline
Salt water, Nail polish in nail polish remover
Brass (Zinc in Copper)
FACTORS IN SOLUTION FORMATION
Intermolecular Forces
When attractions between solute molecules and solvent molecules are strong, solutions are
able to form.
Solute molecules are surrounded by solvent molecules. (solvent cage)
H
H
O
H
H
O
H
H
O
H
H
C
C
O
H
O
H
+
H
O
H
H
H
H
H
O
O
H
H
H
O
H
H
“Like dissolves like”
– polar solvents dissolve polar solutes
– nonpolar solvents dissolve nonpolar solutes
H
2
Enthalpy – another word for chemical heat
When solutes are dissolved, usually heat is given off. Most chemical processes release
heat.
Entropy
- Entropy is disorder
- A system with more disorder has more entropy.
- A messy bedroom has more entropy than a clean bedroom.
- A pyramid of stacked oranges has less entropy than a pile of oranges.
**Systems naturally tend to change from order to disorder. (Entropy always increases.)**
Increase of entropy is a contributing factor as to why solution form.
Consider dissolving salt in water
- Salt crystal is very ordered. (low entropy)
- Salt ions in water are much less ordered. (higher entropy)
Consider blue dye in water
- Molecules in a drop of blue dye are relatively ordered.
- Entropy increases as dye spreads throughout solution.
- Dye molecules will never return to a single drop.
CONCENTRATION AND CONCENTRATION UNITS
Concentration is how much solute is dissolved in a set amount of solvent.
Mass Percent
Definition: Mass % 
mass of solute
 100 %
mass of solution
Example: What is the mass percent of aspirin when 5.02 g of aspirin is dissolved in 231 g of
acetone?
Mass % 
5.02 g
 100 %  2.13 %
5.02 g  231g
Molarity
moles of solute mol

liters of solution
L
- for dilute solutions, liters of solution equals liters of solvent.
Definition: Molarity M  
Example: What is the molarity of the solution when 1.73 mol of NaCl is dissolved 2.14 L?
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Example: What is molarity of the solution when 114.8 g of KBr is dissolved in 538.1 mL of
water?
Remember, we need moles of solute and liters of solvent.
Molarity can be thought of a conversion factor between volume and # of moles.
Example: How many moles of gold(III) nitrate are in 3.75 L of 0.024 M solution?
Example: How many grams of NaF are in 235 mL of a 1.12 M solution?
DILUTIONS
- making a solution of lower concentration from a solution of higher concentration
Question: If a 5.0 M solution of NaCl is available, how does one make 250 mL of
2.0 M NaCl?
Question 1: How many moles of solute do I need in final dilution?
Answer:
mol d
Md 
 mol d  M d  Vd
Vd
mol d  2.0
mol
 0.250L  0.50mol
L
Question 2: What is the source of NaCl in our final dilution?
Answer: The 5.0 M NaCl solution.
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Question 3: How can we get 0.50 molNaCl from a 5.0 M solution?
Answer:
Mc 
Vi 
mol c
mol c
 Vc 
Vc
Mc
0.50mol
 0.10L
5.0mol L
Therefore, to make 250 mL of 2.0 M NaCl, one needs 100 mL of 5.0 M NaCl. Then
add water to make 250 mL solution.
Key to dilution concept:
**Number of moles of solute is the same before and after dilution.**
i. e., molf = moli
i. e., molc = mold
Knowing mol = M  V yields the dilution equation
Mc  Vc = Md  Vd
For any concentration unit, the dilution equation can be written as cc  Vc = cd  Vd
c – concentration
Example: Find the volume of 6.02 M HCl to make 500 mL of 0.125 M HCl.
Lab Safety Aside: Never add water to acid, always add acid to water.
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SOLUTION STOICHIOMETRY
- In chapter 8, we dealt with comparing components of a chemical reaction by converting mass
of substances to moles.
- Now we will consider solutions where we will need to convert volumes to moles to make
comparisons.
SCHEME:
Mass of
reactant
(g)
Mass of
product
(g)
M
Molar
Mass
Moles of
reactant
(mol)
M
molarity
Volume of
reactant
(L)
M
Molar
Mass
Balanced
Equation
Moles of
product
(mol)
M
molarity
Volume of
product
(L)
Neutralization Reactions
Example: How many milliliters of 0.176 M KOH is needed to neutralize 45.3 mL of
0.128 M HCl?
KOH (aq) + HCl (aq)  H2O (l) + KCl (aq)
Precipitation Reactions
Example: For the reaction 2 LiOH (aq) + ZnSO4 (aq)  Zn(OH)2 (s) + Li2SO4 (aq)
Calculate the grams of Zn(OH)2 made when 250 mL of 0.275 M LiOH reacts with
an excess of ZnSO4 solution.
Scheme: vol LiOH  mol LiOH  mol Zn(OH)2  g Zn(OH)2
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TYPES OF SOLUTES
1.) electrolytes
- when dissolved, solution conducts electricity
- H2O without ions is a poor conductor.
- are ionic compounds or acids (usually)
a) strong electrolytes
- Ions completely dissociate from formula unit or lattice.
NaCl (aq) = Na+ (aq) + Cl- (aq)
- Water surrounds ions to dissolve lattice.
b) weak electrolytes
- Ions partially dissociate from formula unit.
HC2H3O2 (aq) + H+ (aq) + C2H3O2- (aq)
a lot
a little
a little
- Equilibrium (balance) exists between dissociated ions and undissociated compounds.
More in Chapter 13.
HC2H3O2 (l) + H2O (l)
2.) nonelectrolytes
- when dissolved, solution is still electrical insulator
- usually molecular compounds
C12H22O11 (s) + H2O (l)  C12H22O11 (aq)
SOLUBILITY
- Amount of solute that can be dissolved into a standard amount of solvent
Example: At 25 C, the solubilities of the following compounds are
Compound Solubility
NaCl
5.47 M
Sugar
6.00 M
Mg(OH)2
0.0017 M
CO2
0.026 M
O2
0.0016 M
- 5.47 moles of NaCl (217 g) can be dissolved in 1 L of H2O
- 0.026 moles of CO2 (1.1 g) can be dissolved in 1 L of H2O
For solid solutes, the process of putting of solute into solution is dissolution.
For solid solutes, the process of a solute coming out of solution is crystallization.
SOME DEFINTIONS
Saturated Solution
- A solution where no more solute can be put into solution.
- Dissolution and crystallization are happening at the same time and at the same rate.
Supersaturated Solution
- Unstable solution with an excess of solute dissolved.
- A small disturbance causes supersaturated solution to crystallize into solid solute and
saturated solution.
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Miscible
- when pairs of liquids mix together in all proportions
- Water and ethanol (grain alcohol) are miscible.
Immiscible
- when pairs of liquids do not mix together at all
- Water and oil are immiscible.
FACTORS AFFECTING SOLUBILITY
Intermolecular Forces
- “like dissolves like”
External Pressure
- high external partial pressures increase solubility of gas in liquid
- Henry’s Law
- The solubility of a gas in a liquid is proportional to the external partial pressure.
c  k  P c – solubility P – pressure k – Henry’s law constant
- important for applications in
deep sea diving
anesthesia
beverage carbonation
Temperature
- Most often higher temperature increases solubility of solid in liquids.
- Most often higher temperature decreases solubility of gas in liquids.
COLLIGATIVE PROPERTIES
- properties that depend only on the number of solute particles and the specific solvent.
- Colligative properties are independent of the specific nature of the solute.
- 4 properties to be examined
1.) Vapor pressure lowering (Raoult’s Law)
2.) Boiling point elevation
3.) Freezing point depression
4.) Osmosis
VAPOR PRESSURE LOWERING
Vapor Pressure – the partial pressure of vapor above its liquid
Compound
Vapor Pressure (at 25 C)
water
0.0313 atm
(23.8 Torr)
gasoline
0.106 atm
(80.46 Torr)
acetone
0.164 atm
(124.4 Torr)
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mercury
2.2 x 10 atm (0.0017 Torr)
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Raoult’s Law
The vapor pressure of solvent is proportional to the mole fraction of the solvent.
xA – mole fraction
PA  x A  PA0
PA – partial pressure
PA0 – partial pressure of pure solvent
- Vapor pressure over solution is an equilibrium between evaporation and condensation.
- Adding nonvolatile component takes up space of surface of solution.
H2O
H2O
H2O
H2O
Cl-
H2O
H2O
H2O
H2O
Na+
H 2O
H2O
H2O
H2O
Cl-
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H 2O
pure water
H2 O
Na+
Na+
Cl-
H2O
salt water
- fewer water molecules have opportunity to escape from surface in salt water
- rate of evaporation slows
- rate of condensation stays the same
- overall fewer molecules go into air; therefore, salt water has lower vapor pressure than
pure water
BOILING POINT ELEVATION
- Addition of solute lowers vapor pressure; therefore, raises boiling point.
- Change in boiling point is proportional to concentration of solute molecules.
- Change in boiling point temperature is independent of specific solute. It depends only
number of solute particles.
Example: Add antifreeze to water to raise boiling point; therefore, coolant can work over a
wider range.
FREEZING POINT DEPRESSION
- Addition of solute disrupts formation of ionic (or molecular) lattice.
- Change in freezing point is proportional to concentration of solute particles.
- Change in freezing point temperature is independent of specific solute. It depends only
number of solute particles.
Example: Putting salt on roads makes salt water, which has lower freezing point. Salt only
works when temperature is above 0 F. (0 F is freezing point of saturated salt
solution.)
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OSMOSIS
Semipermeable Membrane
- membrane which allows only certain substances to flow through
- in biology, cell membranes allow transport of water but not ions, proteins, biomolecules,
etc…
Osmosis occurs when solvent flows across membrane from high concentration to low
concentration.
**Careful! We are considering solvent concentration, not solute concentration.**
H2O
H2O
Cl-
H2O
H2O
H2O
H2O
H2O
H2O
H2 O
H2O
Na
H2O
H2O
+
H2O
salt water
(low water conc.)
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
pure water
(high water conc.)
H2O
Osmotic Pressure - 
- The desire of solvent to flow through membrane creates pressure.
Osmosis
salt water
pure water
not as salty
water

pure water
height in column shows that pure water is pushing on it
demonstrating osmotic pressure - 
- osmotic pressure is proportional to concentration of solute particles
- very sensitive way to measure molar masses of proteins, DNA, polymers, etc …
Reverse Osmosis
Desalination (removing salt from water) can be done using the process known as reverse
osmosis.
Salt water is placed on one side of a semipermeable membrane and an external pressure is
applied to overcome the osmotic pressure against the salt water.