Vocabulary
In SOLUTION we need to define the SOLVENT the component whose physical
state is preserved when solution forms
SOLUTE the other solution component
The CONCENTRATION is most often
expressed by chemists as MOLARITY.
Other common expressions of
concentration are w/w, vol/vol, and
normality.
number of moles of solute
molarity 
number of liters of solution
moles
M
L
mmol
M
mL
1.0 L of water was
used to make 1.0
L of solution.
Notice the water
left over.
CCR, page 206
PROBLEM: Dissolve 5.00 g of NiCl2•6 H2O in enough
water to make 250 mL of solution. Calculate molarity of
the solution and the concentration of each of the ions.
Problem: What mass of oxalic acid, H2C2O4, is required
to make 250. mL of a 0.0500 M solution?
PROBLEM: You have 50.0 mL of 3.0 M NaOH and
you want 0.50 M NaOH. What do you do?
SOLUTION STOICHIOMETRY
Section 5.10
• Zinc reacts with acids
to produce H2 gas.
• Have 10.0 g of Zn
• What volume of 2.50
M HCl is needed to
convert the Zn
completely?
Zinc reacts with acids to produce H2 gas. If you have 10.0 g of
Zn, what volume of 2.50 M HCl is needed to convert the Zn
completely?
Aqueous Solutions
Non-Electrolytes – they dissolve, but won’t conduct electricity.
These are generally polar solids capable of forming hydrogen
bonds
– Sugar, ethanol, ethylene glycol
Strong Electrolytes – Completely dissociates, conducts
electricity well – most ionic solids and strong acids
Weak Electrolytes – Dissolve, ionize to a small extent,
conducts electricity weakly. Weak acids, such as Acetic acid,
ionize only to a small extent, so it are a weak electrolyte.
CH3CO2H(aq) → CH3CO2-(aq) +H+(aq)
Water Solubility of Ionic Compounds
If one ion from the “Soluble
Compound” list is present in a
compound, the compound is
water soluble.
There are three ways to write reactions in aqueous solutions.
Molecular equation:
Show all reactants & products in molecular or ionic form
Zn (s) + CuSO 4(aq)  ZnSO 4(aq) + Cu(s)
Total ionic equation:
Show the ions and molecules as they exist in solution
Zn (s) + Cu
2
aq 
+ SO
24 aq 
 Zn
2
aq 
+ SO
24 aq 
+ Cu (s)
Net ionic equation:
Shows ions that participate in reaction and removes
spectator ions. Spectator ions do not participate in the
reaction.
Zn (s) + Cu
2
aq 
 Zn
2
aq 
+ Cu (s)
Net Ionic Equations
Mg(s)+ 2HCl(aq)→ H2(g) + MgCl2(aq)
The molecular formula above can be written as the total ionic
formula
Mg(s)+ 2H+(aq)+ 2Cl-(aq)→ H2(g)+ Mg2+(aq)+ 2Cl-(aq)
The two Cl- ions are SPECTATOR IONS — they do not
participate. Could have used NO3- for the spectator ion as salts of
nitrates are all soluble.
By leaving out the spectator ions out you get the net ionic reaction
Mg(s) + 2 H+(aq) ---> H2(g) + Mg2+(aq)
ACIDS Table 5.2
A Brönsted-Lowry Acid → H+ in water
Strong Brönsted-Lowry acids are strong electrolytes
HCl
H2SO4
HClO4
HNO3
hydrochloric
sulfuric
perchloric
nitric
HNO3
Weak Brönsted-Lowry acids are weak electrolytes
CH3CO2H
H2CO3
H3PO4
HF
acetic acid (CH3COOH)
carbonic acid
phosphoric acid
hydrofluoric acid
Carbonic Acid
Acetic acid
BASES Table 5.2
Brönsted-Lowry Base → OH- in water
NaOH(aq) → Na+(aq) + OH-(aq)
NaOH is a strong base
Ammonia, NH3 an Important
weak Base
ACIDS
Nonmetal oxides can be acids
CO2(aq) + H2O(l) → H2CO3(aq)
SO3(aq) + H2O(l) → H2SO4(aq)
NO2(aq) + H2O(l) → HNO3(aq)
Acid Rain is an example of nonmetal oxides behaving
as acids. This process can result from burning coal and
oil.
BASES
Metal oxides can be bases
CaO(s)+H2O(l) → Ca(OH)2(aq)
CaO in water. Phenolphthalein indicator shows
a of calcium oxide solution is basic.
You should know the
strong acids & bases
A brief history of Acid-Base
Identification Systems
System
Arrhenius
BrönstedLowry
Lewis
Acid (HCl)
Base (NaOH)
pH, a Concentration Scale
pH: a way to express acidity -- the concentration of H+ in
solution.
Low pH: high [H+]
Acidic solution
Neutral
Basic solution
High pH: low [H+]
pH < 7
pH = 7
pH > 7
The pH Scale
pH = log (1/ [H+]) = - log [H+]
In a neutral solution,
[OH-] = 1.00 x 10-7 M at 25 oC
pH = - log [H+] =
If the [H+] of soda is 1.6 x 10-3 M, the pH is ____.
If the pH of Coke is 3.12, it is _____.
[H+] =
ACID-BASE REACTIONS
Titrations
H2C2O4(aq) + 2 NaOH(aq) → Na2C2O4(aq) + 2 H2O(l)
acid
base
Carry out this reaction using a TITRATION.
Oxalic acid,
H2C2O4
Titration
1. Add solution from the buret.
2. Reagent (base) reacts with
compound (acid) in solution
in the flask.
3. Indicator shows when exact
stoichiometric reaction has
occurred.
4. Net ionic equation
H+ + OH- --> H2O
5. At equivalence point
moles H+ = moles OH-
PROBLEM: Standardize a solution of NaOH — i.e., accurately
determine its concentration. 1.065 g of H2C2O4 (oxalic acid)
requires 35.62 mL of NaOH for titration to an equivalence
point. What is the concentration of the NaOH?
PROBLEM : Use standardized NaOH to determine the amount
of an acid in an unknown. Apples contain malic acid, C4H6O5.
76.80 g of apple requires 34.56 mL of 0.663 M NaOH for
titration. What is weight % of malic acid?
C4H6O5(aq) + 2NaOH(aq) → Na2C4H4O5(aq) + 2 H2O(l)
Types of Reactions:
1. Combination Reactions
• More than one reactant, one product
2. Decomposition Reactions
• Single reactant, more than one product
3. Displacement Reactions
• One element displaces another from a compound
4. Redox – Oxidation Reduction Reactions
• Oxidation numbers of some elements change; at least one element
must increase and one must decrease in oxidation number.
5. Metathesis Reactions - Exchange Reactions
• Precipitation: products include an insoluble substance which
precipitates from solution as a solid
• Acid-base neutralization: product is a salt and water
• Gas formation – primarily the reaction of metal carbonates
OXIDATION NUMBERS
NH3
ClOH3PO4
MnO4Cr2O72-
Recognizing a Redox Reaction
2 Al(s) + 3 Cu2+(aq) → 2 Al3+(aq) + 3 Cu(s)
Oxidation-Reduction Reactions
Thermite reaction
Fe2O3(s) + 2Al(s) → 2 Fe(s) + Al2O3(s)
2Al(s) + 3Cu2+(aq) → 2Al3+(aq)+ 3Cu(s)
2 H2(g) + O2(g) → 2H2O(l)
In all reactions if something has been oxidized then
something has also been reduced.
Redox reactions are characterized by ELECTRON TRANSFER
between an electron donor and electron acceptor.
Transfer leads to
1. increase in oxidation number of some element = OXIDATION
2.decrease in oxidation number of some element =
REDUCTION
Chemical Reactions in Water
Metathesis
• EXCHANGE REACTIONS
The anions exchange places between
cations.
AX + BY
AY + BX
Precipitation
Pb(NO3)2(aq) + 2 KI(aq) → PbI2(s) + 2KNO3(aq)
Pb2+(aq) + 2 I-(aq) → PbI2(s)
Neutralization:
NaOH(aq) + HCl(aq)→ NaCl(aq)+ H2O(l)
OH-(aq) + H+(aq)
→ H2O(lq)
Gas Formation
MgCO3(s)+ 2HCl(aq) → 2Mg(Cl)2(aq)+ H2O(l) + CO2(g)