Chem 1
Chemistry in Solutions:
Chapter 4
Atoms,
Molecules,
and Ions
Solutions:
• Homogeneous mixtures of two
or more pure substances.
• The solvent is present in
greatest abundance.
• All other substances are
solutes.
• Water is the most common
solvent. If solvent is not
specified, presume it is water.
Atoms,
Molecules,
and Ions
Solubility
• Solids can be soluble is water (like sugar or
sodium chloride) and insoluble (like silicon dioxide,
sand, and calcium carbonate, chalk).
Atoms,
Molecules,
and Ions
Dissociation
• When an ionic
substance dissolves
in water, the solvent
interacts with the
individual ions from
the crystal and
solvates them.
• This process is called
dissociation.
• Some molecular compounds may also
Atoms,
undergo dissociation (ionization) in
Molecules,
and Ions
aqueous solution.
Solubility
• Liquids can be soluble in water (like ethanol) and
insoluble (like gasoline, a mixture of
hydrocarbons). Soluble liquids are miscible, and
mutually insoluble liquids are immiscible.
Atoms,
Molecules,
and Ions
Solubility
• Ammonia gas (NH3) and hydrogen chloride gas
(HCl) are very well soluble in water, while oxygen
and nitrogen gases (O2 and N2) are only poorly
soluble.
Atoms,
Molecules,
and Ions
Electrolytes
An electrolyte is a substance that dissolves
in water and dissociates into ions. Its solution
conducts electricity.
Atoms,
Molecules,
and Ions
Non-Electrolytes
A nonelectrolyte does not dissociate into ions. A
nonelectrolyte solution does not conduct
electricity.
.
Insoluble chemicals are considered non-electrolytes in Chem 1.
Atoms,
Molecules,
and Ions
Strong and Weak Electrolytes
A strong electrolyte will
completely dissolve in
water, dissociating into ions
A weak electrolyte
will partially
dissolve in water, or
partially ionize. ~110% ionization.
Solution will contain
both ions and
molecules of the
electrolyte.
Atoms,
Molecules,
and Ions
Electrolytes and Nonelectrolytes
Table 4.3
Soluble ionic
compounds are all
electrolytes:
NaCl(aq)  Na+(aq) + Cl-(aq)
Atoms,
Molecules,
and Ions
Electrolytes and Nonelectrolytes
Molecular compounds tend
to be nonelectrolytes.
Example: CH3OH (methanol)
Exceptions: acids, NH3
Atoms,
Molecules,
and Ions
Strong and Weak
Electrolytes
• A weak electrolyte only
partially dissociates
when dissolved in water.
NH3 + H2O
NH4+ + OH-
ammonia
CH3COOH
acetic acid
CH3COO- + H+
Some equilibrium is
established, net
concentrations of the
reactants and
products will not
change.
Atoms,
Molecules,
and Ions
Strong and Weak
Electrolytes
• A strong electrolyte
dissociates completely
when dissolved in
water.
HCl(aq)  H+(aq) + Cl-(aq)
NaOH(aq)  Na+(aq) + OH-(aq)
Atoms,
Molecules,
and Ions
Strong Electrolytes Are…
1) Seven common strong acids
Most other acids are weak
Atoms,
Molecules,
and Ions
Acids:
Arrhenius defined acids as substances that produce
H+(aq) when dissolved in water.
Lewis defined acids as electron acceptors
Strong acids ionize in water
completely:
HCl(aq)  H+(aq) + Cl-(aq)
Weak acids ionize only
partially:
H(C2H3O2)(aq) ⇄ H+(aq) +
C2H3O2-(aq)
Atoms,
Molecules,
and Ions
Acids
There are seven
common strong acids:
Hydrochloric, HCl(aq)
Hydrobromic, HBr(aq)
Hydriodic, HI(aq)
Nitric (HNO3)
Sulfuric, (H2SO4)
Chloric (HClO3)
Perchloric (HClO4)
All other common acids are weak (HF, H2S, HClO,
HClO2, H2CO3, H3PO4, all organic acids, etc.)
Atoms,
Molecules,
and Ions
Strong Electrolytes Are…
2) Eight strong bases
Other metal hydroxides are insoluble weak bases.
Ammonia (NH3) is a soluble weak base.
Atoms,
Molecules,
and Ions
Bases:
Arrhenius defined bases as
substances that produce
OH−(aq) when dissolved in
water.
Lewis defined bases as
electron donors +
NaOH(aq)  Na (aq) + OH-(aq)
strong base
NH3(aq) + H2O(l) ⇄ NH4+(aq) + OH -(aq)
weak base
Atoms,
Molecules,
and Ions
Strong Bases
The 8 strong bases are the soluble ionic
compounds with the hydroxide anion, OH−
• Alkali metals (Li, Na, K, Rb, Cs): MOH
• Heavy alkali earth metals (Ca, Sr, Ba): M(OH)2
Atoms,
Molecules,
and Ions
Weak Bases
Common inorganic weak bases include:
• Ammonia (NH3): NH3(aq) + H2O(l) ⇄ NH4+(aq) + OH (aq)
-
• Poorly soluble metal hydroxides:
Mg(OH)2(s) ⇄ Mg2+(aq) + 2OH-(aq)
Al(OH)3(s) ⇄ Al3+(aq) + 3OH-(aq)
magnesium and aluminum hydroxides
Atoms,
Molecules,
and Ions
Strong Electrolytes Are…
3) Soluble ionic compounds
Atoms,
Molecules,
and Ions
Practice Problem
Classify the following soluble compounds as strong
electrolytes, weak electrolytes, or non-electrolytes. Write
ionization reactions in water (where applicable).
1) HNO3 =
2) KOH =
3) C2H5OH =
4) HCOOH =
5)NH3 =
6) N2 =
Atoms,
Molecules,
and Ions
Practice Problem
Classify the following soluble compounds as strong
electrolytes, weak electrolytes, or non-electrolytes. Write
ionization reactions in water (where applicable).
1)
2)
3)
4)
HNO3 = strong acid, HNO3(aq) → H+(aq) + NO3-(aq)
KOH = strong base, KOH(aq) → K+(aq) + OH-(aq)
C2H5OH = molecular compound, non-electrolyte
HCOOH = weak acid,
HCOOH(aq) ⇄ HCOO-(aq) + H+(aq)
5) NH3 = weak base,
NH3(aq) + H 2O(l) ⇄ NH 4+(aq) + OH-(aq)
6) N2 = molecular species, non-electrolyte
Atoms,
Molecules,
and Ions
Precipitation Reactions
When ions are mixed
together and form
insoluble compounds
(as predicted by the
solubility guidelines), a
precipitate is formed.
Silver chloride (AgCl) is insoluble; mixing of
solutions containing Ag+(aq) and Cl-(aq) will result in
the precipitation of AgCl(s).
Atoms,
Molecules,
and Ions
Exchange (Metathesis) Reactions
• Metathesis comes from a Greek word that
means “totranspose”
AgNO3 (aq) + KCl (aq) 
Atoms,
Molecules,
and Ions
Exchange (Metathesis) Reactions
• Metathesis comes from a Greek word that
means “totranspose”
• The reactants exchange, or transpose, ions
AgNO3 (aq) + KCl (aq) 
Atoms,
Molecules,
and Ions
Exchange (Metathesis) Reactions
• Metathesis comes from a Greek word that
means “totranspose”
• The reactants exchange, or transpose, ions
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
Atoms,
Molecules,
and Ions
Molecular Equation
This “molecular” equation lists the reactants
and products as full formulas.
AgNO3 (aq) + KCl (aq)  AgCl (s) +KNO3 (aq)
Atoms,
Molecules,
and Ions
Full Ionic Equation
• In the ionic equation all strong soluble electrolytes
(strong acids, strong bases, and soluble salts) are
dissociated into their ions.
• This is a more accurate reflection of the species
found in the solution.
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) 
AgCl (s) + K+ (aq) + NO3- (aq)
Atoms,
Molecules,
and Ions
Net Ionic Equation
• To form the net ionic equation, cross out any species
that are present in the same form on the reactant
and product side of the equation.
Ag+(aq) + NO 3-(aq) + K+(aq) + Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
Atoms,
Molecules,
and Ions
Net Ionic Equation
• To form the net ionic equation, cross out any species
that are present in the same form on the reactant
and product side of the equation.
• The only things left in the equation are those things
that change (i.e., react) during the course of the
reaction.
Ag+(aq) + NO 3-(aq) + K+(aq) + Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
Ag+(aq) + Cl-(aq)  AgCl (s)
Atoms,
Molecules,
and Ions
Net Ionic Equation
• To form the net ionic equation, cross out any species
that are present in the same form on the reactant
and product side of the equation.
• The only things left in the equation are those things
that change (i.e., react) during the course of the
reaction.
• Those things that didn’t change are called spectator
ions.
Ag+(aq) + NO -(aq) + K+
3
(aq)
+ Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
Atoms,
Molecules,
and Ions
Precipitation Reactions
1.
2.
3.
4.
5.
6.
If two soluble ionic species (two soluble salts) are mixed,
there is the possibility a precipitate may form.
Predict the formulas of the possible products of the
exchange reaction of the two starting species.
If both products are soluble, there will be no chemical reaction (NR). Instead, physical mixing of the solutions will occur.
If one or both products of the exchange is/are insoluble,
there will be a precipitation chemical reaction.
To write the full ionic equation, dissociate all strong
electrolytes into ions. Leave weak electrolytes, nonelectrolytes, and insoluble compounds in molecular form.
To obtain the net ionic equation, cross out spectator ions
(which are dissociated on each side of the equation).
Check if the coefficients in the net ionic equation
Atoms,
Molecules,
can be simplified.
and Ions
Practice Problem
Predict the products (if any) of the following reactions
and write balanced equations in molecular, full ionic,
and net ionic form where applicable:
1) NaBr(aq) + Al(NO3)3(aq) 
2) CaI2(aq) + AgNO3(aq) 
Atoms,
Molecules,
and Ions
Practice Problem
Predict the products (if any) of the following reactions
and write balanced equations in molecular, full ionic,
and net ionic form where applicable:
1) NaBr(aq) + Al(NO3)3(aq)  NR
Exchange rxn results in soluble ionic compound
2) CaI2(aq) + AgNO3(aq) 
Ca+(aq) + 2I- (aq) + 2Ag+(aq) + NO 3- (aq) 
NO3- (aq) + Ca+(aq) + 2AgI (s)
Ag+(aq) + I-(aq)  AgI(s)
Atoms,
Molecules,
and Ions
Solubility Rules
Atoms,
Molecules,
and Ions
Solubility Rules
Atoms,
Molecules,
and Ions
Practice Problem
A solution containing 4.73 g of BaCl2 is mixed with a solution
containing 5.88 g of MgSO4.
a) How many grams of precipitate will form? Name the
precipitate.
b) Which reagent will be left over and how many grams?
A: (a) 6.47 g BaSO4 (Barium sulfate)
(b) 2.54 g MgSO4
Atoms,
Molecules,
and Ions
ICE Reaction Tables
▪ Some reactions have stoichiometric coefficients
that are all ones (which appears like no
coefficients at all):
Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s)
▪ Stoichiometric calculations for such a reaction
may be simplified by using a so called ICE
reaction table.
▪ In such a table, three lines below the reaction
equation list moles of chemicals that are Initial,
Change, and End amounts.
Atoms,
Molecules,
and Ions
ICE Reaction Tables
How many moles of products will be obtained
from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)?
What will be left over and how much?
Atoms,
Molecules,
and Ions
ICE Reaction Tables
How many moles of products will be obtained
from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)?
What will be left over and how much?
Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s)
Atoms,
Molecules,
and Ions
ICE Reaction Tables
How many moles of products will be obtained
from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)?
What will be left over and how much?
Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s)
0
0
Ini. 2.55 mol 1.20 mol
Atoms,
Molecules,
and Ions
ICE Reaction Tables
How many moles of products will be obtained
from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)?
What will be left over and how much?
Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s)
Ini. 2.55 mol 1.20 mol
0
0
Ch. -1.20 mol -1.20 mol
+1.20 mol +1.20 mol
Atoms,
Molecules,
and Ions
ICE Reaction Tables
How many moles of products will be obtained
from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)?
What will be left over and how much?
Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s)
Ini. 2.55 mol 1.20 mol
0
0
Ch. -1.20 mol -1.20 mol
+1.20 mol +1.20 mol
End 1.35 mol
0
1.20 mol 1.20 mol
Atoms,
Molecules,
and Ions
ICE Reaction Tables
How many moles of products will be obtained
from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)?
What will be left over and how much?
Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s)
Ini. 2.55 mol 1.20 mol
0
0
Ch. -1.20 mol -1.20 mol
+1.20 mol +1.20 mol
End 1.35 mol
0
1.20 mol 1.20 mol
Answer: 1.20 mol Na2SO4 and 1.20 mol FeS will be
obtained, and 1.35 mol Na2S will be left over.
Atoms,
Molecules,
and Ions
Acids&Bases
Arrhenius defined acids as
substances that produce
H+(aq) when dissolved in
water.
Arrhenius defined bases as
substances that produce
OH−(aq) when dissolved in
water.
Strong acids ionize in water completely:
HCl(aq)  H+(aq) + Cl-(aq)
NaOH(aq)  Na+(aq) + OH-(aq)
strong base
Weak acids ionize only partially:
H(C2H3O2)(aq) ⇄ H +(aq) + C 2H 3O 2-(aq)
NH3(aq) + H 2O(l) ⇄ NH 4+(aq) + OH-(aq)
weak base
Atoms,
Molecules,
and Ions
Acid-Base Reactions
An acid reacts with a base to form a salt and,
usually, water.
HCl + NaOH  NaCl + H2O
Atoms,
Molecules,
and Ions
Acid-Base Reactions
An acid reacts with a base to form a salt and,
usually, water.
HCl + NaOH  NaCl + H2O
3H2SO4 + 2Al(OH)3  Al2(SO4)3 + 6H2O
Atoms,
Molecules,
and Ions
Acid-Base Reactions
An acid reacts with a base to form a salt and,
usually, water.
HCl + NaOH  NaCl + H2O
3H2SO4 + 2Al(OH)3  Al2(SO4)3 + 6H2O
CH3COOH + NH3  (NH4)(CH3COO)
ammonium acetate and no water
Atoms,
Molecules,
and Ions
Acid-Base Reactions
An acid reacts with a base to form a salt and,
usually, water.
HCl + NaOH  NaCl + H2O
3H2SO4 + 2Al(OH)3  Al2(SO4)3 + 6H2O
CH3COOH + NH3  (NH4)(CH3COO)
ammonium acetate and no water
Acid-base reactions are also called
neutralization reactions because salts are
generally neutral.
Atoms,
Molecules,
and Ions
Salts
Salt is any ionic compound other than metal
oxide or hydroxide. (Metal oxides and
hydroxides are bases.)
Atoms,
Molecules,
and Ions
Salts
Salt is any ionic compound other than metal
oxide or hydroxide. (Metal oxides and
hydroxides are bases.)
A salt can be derived from an acid and a base.
The base provides the cation of the salt, and
the acid provides the anion of the salt.
Atoms,
Molecules,
and Ions
Salts
Salt is any ionic compound other than metal
oxide or hydroxide. (Metal oxides and
hydroxides are bases.)
A salt can be derived from an acid and a base.
The base provides the cation of the salt, and
the acid provides the anion of the salt.
Examples:
NaCl is a salt of NaOH and HCl
Atoms,
Molecules,
and Ions
Salts
Salt is any ionic compound other than metal
oxide or hydroxide. (Metal oxides and
hydroxides are bases.)
A salt can be derived from an acid and a base.
The base provides the cation of the salt, and
the acid provides the anion of the salt.
Examples:
NaCl is a salt of NaOH and HCl
Pb(NO3)2 is a salt of Pb(OH)2 and HNO3
Atoms,
Molecules,
and Ions
Salts
Salt is any ionic compound other than metal
oxide or hydroxide. (Metal oxides and
hydroxides are bases.)
A salt can be derived from an acid and a base.
The base provides the cation of the salt, and
the acid provides the anion of the salt.
Examples:
NaCl is a salt of NaOH and HCl
Pb(NO3)2 is a salt of Pb(OH)2 and HNO3
(NH4)3PO4 is a salt of NH3 and H3PO4
Atoms,
Molecules,
and Ions
Strong Acid + Strong Base
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
acid
base
salt
water
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) →
Na+(aq) + Cl-(aq) + H2O(l) {Full ionic equation}
H+(aq) + OH-(aq) → H2O(l)
(This net ionic equation is realized for the reaction of any
strong acid with any strong base.)
Atoms,
Molecules,
and Ions
Strong Acid + Strong Base
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
acid
base
salt
water
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) →
Na+(aq) + Cl-(aq) + H2O(l) {Full ionic equation}
H+(aq) + OH-(aq) → H2O(l)
(This net ionic equation is realized for the reaction of any
strong acid with any strong base.)
Atoms,
Molecules,
and Ions
Ionic Equations with Weak Electrolytes
When writing ionic equations, we leave weak
electrolytes, non-electrolytes, and insoluble
compounds in molecular form.
2HNO3(aq) + Mg(OH)2(s) → Mg(NO3)2(aq) + 2H2O(l)
Atoms,
Molecules,
and Ions
Strong Acids & Solubility…
There are seven
common strong acids:
Hydrochloric, HCl(aq)
Hydrobromic, HBr(aq)
Hydriodic, HI(aq)
Nitric (HNO3)
Sulfuric, (H2SO4)
Chloric (HClO3)
Perchloric (HClO4)
Atoms,
Molecules,
and Ions
Ionic Equations with Weak Electrolytes
When writing ionic equations, we leave weak
electrolytes, non-electrolytes, and insoluble
compounds in molecular form. (In this
example we are looking at a weak base)
2HNO3(aq) + Mg(OH)2(s) → Mg(NO3)2(aq) + H2O(l)
2H+(aq) + 2NO3-(aq) + Mg(OH)2(s) →
Mg2+(aq) + 2NO3-(aq) + H2O(l)
2H+(aq) + Mg(OH)2(s) → Mg2+(aq) + 2H2O(l) Atoms,
Molecules,
and Ions
insoluble
Practice Problem
Predict the products of the following
reactions and write balanced equations in
the molecular, full ionic, and net ionic forms.
a) H2S (aq) + NaOH (aq) 
b) Zn(OH)2(s) + H3PO4(aq) 
c) NH3(aq) + CH3COOH(aq) 
Atoms,
Molecules,
and Ions
Practice Problem
Predict the products of the following reactions and
write balanced equations in the molecular, full ionic,
and net ionic forms.
a) H2S (aq) + NaOH (aq) 
Molecular equation: H2S (aq) + NaOH (aq)  Na2S(aq) + 2H2O(l)
Full ionic equation: H2S (aq) + 2Na+ + 2OH- (aq) 2Na+(aq) + S2-(aq) + 2H2O(l)
Net ionic equation: H2S (aq) + 2OH- (aq)  S2-(aq) + 2H2O(l)
Atoms,
Molecules,
and Ions
Practice Problem
Predict the products of the following reactions
and write balanced equations in the molecular,
full ionic, and net ionic forms.
b) Zn(OH)2(s) + H3PO4(aq) 
Molecular equation: 3Zn(OH)2(s) + 2H3PO4(aq) Zn3(PO4)2(s) + 6H2O(l)
There is no ionic equation here, because all reactants and products are
either weak electrolytes or insoluble substances.
Atoms,
Molecules,
and Ions
Practice Problem
Predict the products of the following reactions
and write balanced equations in the molecular,
full ionic, and net ionic forms.
c) NH3(aq) + CH3COOH(aq) 
Molecular Equation: NH3(aq) + CH3COOH(aq)  (NH4)(CH3COO)(aq)
Atoms,
Molecules,
and Ions
Strong Acid + Salt of Weak Acid
Product is the salt of the strong acid and the
weak acid of the salt
(The strong acid “forces”the weak acid from its
salt).
NaF(aq) + HCl(aq) → NaCl(aq) + HF(aq)
salt of HF
strong acid
salt of HCl
weak acid
Atoms,
Molecules,
and Ions
Strong Acid + Salt of Weak Acid
Product is the salt of the strong acid and the
weak acid of the salt
(The strong acid “forces”the weak acid from its
salt).
NaF(aq) + HCl(aq) → NaCl(aq) + HF(aq)
salt of HF
strong acid
salt of HCl
weak acid
Na+(aq)+F-(aq)+ H+(aq)+Cl-(aq) → Na+(aq)+Cl-(aq) + HF (aq)
Atoms,
Molecules,
and Ions
Strong Acid + Salt of Weak Acid
Product is the salt of the strong acid and the weak acid of the
salt
(The strong acid “forces”the weak acid from its salt).
NaF(aq) + HCl(aq) → NaCl(aq) + HF(aq)
salt of HF
strong acid
salt of HCl
weak acid
Na+(aq)+F-(aq)+ H+(aq)+Cl-(aq) → Na+(aq)+Cl-(aq) + HF(aq)
F-(aq) + H+(aq) → HF(aq) {Net ionic equation}
(association of ions to make weak acid)
Atoms,
Molecules,
and Ions
Gas-Forming Reactions
• Carbonates (salts with CO32-) react with strong
acids to form a weak carbonic acid (H2CO3):
CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq)
Atoms,
Molecules,
and Ions
Gas-Forming Reactions
• Carbonates (salts with CO32-) react with strong
acids to form the weak carbonic acid (H2CO3):
CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq)
• Carbonic acid is not only weak, but also unstable:
H2CO3(aq)  CO2
(g) + H2O (l)
Atoms,
Molecules,
and Ions
Gas-Forming Reactions
• Carbonates (salts with CO32-) react with strong
acids to form the weak carbonic acid (H2CO3):
CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq)
• Carbonic acid is not only weak, but also unstable:
H2CO3(aq)  CO2
(g) + H2O (l)
• The overall reaction is
CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)
Atoms,
Molecules,
and Ions
Gas-Forming Reactions
• Carbonates (salts with CO32-) react with strong
acids to form the weak carbonic acid (H2CO3):
CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq)
• Carbonic acid is not only weak, but also unstable:
H2CO3(aq)  CO2
(g) + H2O (l)
• The overall reaction is
CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)
• Sulfites (salts with SO32-) similarly produce SO 2(g)
and sulfides (with S2-) produce H2S(g):
FeS(s) + 2 HI (aq) FeI2 (aq) + H2S(g)
Atoms,
Molecules,
and Ions
Strong Base + Salt of Weak Base
Product is the salt of the strong base and the weak
base of the salt
2NH4Br + Ca(OH)2  2NH3
salt of NH3
strong base
weak base
+
CaBr2 + 2H2O
salt of Ca(OH)2
Atoms,
Molecules,
and Ions
Strong Base + Salt of Weak Base
Product is the salt of the strong base and the weak
base of the salt
2NH4Br + Ca(OH)2  2NH3
salt of NH3
strong base
+
weak base
CaBr2 + 2H2O
salt of Ca(OH)2
MgSO4(aq) + 2KOH(aq)  Mg(OH)2(s) + K2SO4(aq)
salt of Mg(OH)2
strong base
weak base
salt of KOH
Atoms,
Molecules,
and Ions
Strong Base + Salt of Weak Base
Product is the salt of the strong base and the weak
base of the salt
2NH4Br + Ca(OH)2  2NH3
salt of NH3
strong base
+
weak base
CaBr2 + 2H2O
salt of Ca(OH)2
MgSO4(aq) + 2KOH(aq)  Mg(OH)2(s) + K2SO4(aq)
salt of Mg(OH)2
strong base
weak base
salt of KOH
The last reaction can also be understood as precipitation:
Mg2+(aq) + 2OH–(aq)  Mg(OH)2(s)
Atoms,
Molecules,
and Ions
Practice Problem
Predict the products of the following reactions and
write balanced equations in molecular form:
a) Li2SO3 (aq) + H2SO4 (aq) 
•
Li2SO3 (aq) + H2SO4 (aq) Li2SO4(aq) + H2SO3(aq)
b) NaOH (aq) + Fe(NO3)3 (aq) 
•
NaOH (aq) + Fe(NO3)3 (aq) Fe(OH)3(s) + 3NaNO3(aq)
c) Mg(OH)2 (s) + KNO3 (aq) 
• Mg(OH)2 (s) + KNO3 (aq) NR
Atoms,
Molecules,
and Ions
Strong Acids & Solubility…
There are seven
common strong acids:
Hydrochloric, HCl(aq)
Hydrobromic, HBr(aq)
Hydriodic, HI(aq)
Nitric (HNO3)
Sulfuric, (H2SO4)
Chloric (HClO3)
Perchloric (HClO4)
Atoms,
Molecules,
and Ions
Polyprotic Acids
Many acids contain several acidic hydrogens.
Such acids are called polyprotic.
Most of them are weak.
Polyprotic acids in water dissociate in steps.
Step 1: H3PO4 (aq) ⇄ H + (aq) + H2PO4- (aq)
Step 2: H2PO4- (aq) ⇄ H + (aq) + HPO42- (aq)
Step 3: HPO42- (aq) ⇄ H + (aq) + PO43- (aq)
Dissociation of all weak acids in water is
incomplete.
Atoms,
Molecules,
and Ions
Polyprotic Acids
If a strong base is gradually added to a polyprotic
acid, the acid is neutralized in steps.
Step 1: H3PO4 + KOH  KH2PO4 + H2O
Step 2: KH2PO4 + KOH  K2HPO4 + H2O
Step 3: K2HPO4 + KOH  K3PO4 + H2O
Neutralization reactions are one-sided (complete) 
unlike the dissociation of weak electrolytes ⇄
The addition of a strong base makes
Atoms,
Molecules,
the neutralization reaction complete.
and Ions
Nomenclature of Salts of Polyprotic Acids
KH2PO4 , K2HPO4 , and K3PO4 are three salts
formed form triprotic acid H3PO4 and base KOH.
KH2PO4 = potassium dihydrogen phosphate
K2HPO4 = potassium hydrogen phosphate
K3PO4 = potassium phosphate
H2PO4- = dihydrogen phosphate anion
HPO42- = hydrogen phosphate anion
PO43- = phosphate anion
Atoms,
Molecules,
and Ions
Dissociation of Salts of Polyprotic Acids
In the salts of polyprotic acids with remaining H, only
metal (and NH4 ) dissociate completely in water:
+
KH2PO4 (aq)  K+(aq) + H2PO4- (aq)
K2HPO4 (aq)  2K+(aq) + HPO42- (aq)
K3PO4 (aq)  3K+(aq) + PO43- (aq)
H2PO4- and HPO42- are very weak acids and their
own dissociation is negligible
Atoms,
Molecules,
and Ions
Sequential Reactions
If the product of one reaction is a reactant for
another reaction, we refer to the reactions as
sequential and theycan be added to give an
overall reaction equation.
Step 1: H3PO4 + KOH  KH2PO4 + H2O
Step 2: KH2PO4 + KOH  K2HPO4 + H2O
Step 3: K2HPO4 + KOH  K3PO4 + H2O
Overall: H3PO4 + 3KOH  K3PO4 + 3H2O
Atoms,
Molecules,
and Ions
Stoichiometry in Steps
In a stoichiometric problem with sequential
reactions, we consider the first step first – we find
the limiting and excess reactants for the 1st step,
the amounts of products formed, and the amount
leftover after the 1st step. Then, if the chemicals
needed for the 2nd step are present after the
completion of the 1st step, the 2nd step may start,
etc. A reaction sequence may stop at any step
depending on the initial amounts of reactants.
Atoms,
Molecules,
and Ions
Practice Problem
i)
What salts can be formed from a reaction of
H2CO3 and NaOH?
ii) Calculate the moles of each salt after the reaction
of the following:
a) 0.25 mol H2CO3 and 0.25 mol NaOH
b) 0.25 mol H2CO3 and 0.34 mol NaOH
c) 0.25 mol H2CO3 and 0.60 mol NaOH
Atoms,
Molecules,
and Ions
Oxidation-Reduction Reactions
• An oxidation occurs when
an atom or ion loses
electrons:
Zn → Zn2+ + 2e-
OIL RIG
• A reduction occurs when
an atom or ion gains
electrons:
Cu2+ + 2e- → Cu
• One cannot occur without
the other:
Zn + Cu2+ → Cu + Zn2+
Atoms,
Molecules,
and Ions
Redox
Reactions
Oxidationreduction
reactions are
referred to as
redox
reactions.
Atoms,
Molecules,
and Ions
Redox Reactions
• CuSO4 in solution
(blue hue).
• Submerge Zn strip.
• Zinc metal has less of
an affinity for its
electrons than metallic
copper does.
• Zinc slowly etched
from surface (in sol’n)
and metallic Cu plates
Atoms,
onto the strip. Molecules,
and Ions
Oxidation Numbers
In order to keep track of what loses electrons and what
gains them, we assign oxidation numbers (oxidation
states) to elements:
Zn + Cu2+ → Cu + Zn2+
Atoms,
Molecules,
and Ions
Assigning Oxidation Numbers
1. Atoms or molecules in elemental form always
have an oxidation number of 0.
2. For any monatomic ion, the oxidation number
equals the charge of the ion.
3. Non-metals usually have negative oxidation
numbers, but can be positive:
a) O is usually -2; (exception – peroxides of H,
alkali and alkaline earth metals, where O is -1);
b) H is +1 when bonded to non-metals and -1
when bonded to metals and metalloids;
c) F is always -1;
d) Cl, Br, I are usually -1 (exceptions: compounds
with F and O, where Cl, Br, I are positive).
Atoms,
Molecules,
and Ions
Assigning Oxidation Numbers
4a. The sum of the oxidation numbers in a neutral compound
is 0.
4b. The sum of the oxidation numbers in a polyatomic ion is
the charge on the ion.
5. Metals always have positive oxidation numbers in
compounds:
i) +1 for group 1 (Li, Na, K, Rb, Cs) and Ag
ii) +2 for group 2 (Be, Mg, Ca, Sr, Ba) and Zn.
iii) +3 for groups 3 and 13 (Al, Sc, lanthanides, actinides).
iv) Oxidation numbers are variable for transition metals, but
not more than the group number and commonly +2 &+3.
6. The first element in a formula is usually electropositive, and
the last is electronegative. Exceptions: NH3, organic
compounds.
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
Zn
H2
NO2
H 2 O2
NH3
CaH2
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0.
H2
NO2
H 2 O2
NH3
CaH2
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0.
H2
1. Atoms or molecules in elemental form always have an oxidation number of 0.
NO2
H 2 O2
NH3
CaH2
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0.
H2 1. Atoms or molecules in elemental form always have an oxidation number of 0.
NO2 a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1)
H2O2
NH3
CaH2
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0.
H2 1. Atoms or molecules in elemental form always have an oxidation number of 0.
NO2 a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1)
H2O2 exception – peroxides of H, alkali and alkaline earth metals, where O is -1
NH3
CaH2
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0.
H2 1. Atoms or molecules in elemental form always have an oxidation number of 0.
NO2 a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1)
H2O2 exception – peroxides of H, alkali and alkaline earth metals, where O is -1
NH3 H is +1 when bonded to non-metals
CaH2
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0.
H2 1. Atoms or molecules in elemental form always have an oxidation number of 0.
NO2 a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1)
H2O2 exception – peroxides of H, alkali and alkaline earth metals, where O is -1
NH3 H is +1 when bonded to non-metals
Atoms,
Molecules,
a n d Ions
CaH2 H is +1 when bonded to non-metals and -1 when bonded to metals and metallo i d s
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
OF2
Cl2O
P4O6
Cr2O72Ti2(SO4)3
CH2O
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
OF2 F is always -1
Cl2O
P4O6
Cr2O72Ti2(SO4)3
CH2O
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
OF2 F is always -1
Cl2O Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive)
P4O6
Cr2O72Ti2(SO4)3
CH2O
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
OF2 F is always -1
Cl2O Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive)
P4O6 The sum of the oxidation numbers in a neutral compound is 0.
Cr2O72Ti2(SO4)3
CH2O
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
OF2 F is always -1
Cl2O Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive)
P4O6 The sum of the oxidation numbers in a neutral compound is 0.
Cr2O72- The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.
Ti2(SO4)3
CH2O
Atoms,
Molecules,
and Ions
Lecture Problem
Determine the oxidation numbers for all elements in the
following species:
OF2 F is always -1
Cl2O Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive)
P4O6 The sum of the oxidation numbers in a neutral compound is 0.
Cr2O72- The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.
Ti2(SO4)3
CH2O
The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.
Atoms,
Molecules,
and Ions
Oxidation of Metals
Metals can be oxidized by non-metals in
combination reactions:
2Ca + O2 → 2CaO
2Ca(s) + O2(g)
2Ca0 + O02 → 2Ca2+O2-
2CaO(s)
Atoms,
Molecules,
and Ions
Metals can also be oxidized by the H+ cations from
acids:
Mg(s) + 2HCl(aq) → MgCl2 (aq) + H2(g) {molecular}
Mg(s) + 2H+(aq) + 2Cl-(aq) → Mg2+(aq) + 2Cl-(aq) + H2(g) {full ionic}
Mg(s) + 2H+(aq) → Mg2+(aq) + H2(g) {net ionic equation}
This is a
displacemnet
(substitution)
reaction:
Mg displaces
(substitues) H in a
compound with Cl as
it is oxidized.
As a result,
magnesium metal
chemically dissolves
Atoms,
in acid.
Molecules,
and Ions
Metals can also be oxidized by aqueous solutions of other salts:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2 (aq) + 2Ag(g) {molecular}
Cu(s) + 2Ag+(aq) + 2NO3-(aq) → 2Ag(s) + Cu2+(aq) + 2NO3-(aq) {full ionic}
Cu(s) + 2Ag+(aq) → 2Ag(s) + Cu2+(aq) {net ionic equation}
In this
reaction,
silver ions
oxidize
copper metal.
Atoms,
Molecules,
and Ions
Activity Series
Based on the ease of oxidation, metals and hydrogen are ranked in an
activity series. Metals that are easily oxidized are chemically more reactive
and found at the top (ACTIVE); less reactive metals are at the bottom.
Atoms,
Molecules,
and Ions
Where would Zn and Cu be relative to each other?
Atoms,
Molecules,
and Ions
Activity Series
• Easily oxidized metals prefer
to be cations; less reactive
metals prefer to be neutral.
• Any metal on the list can be
oxidized by the ions of
elements below it. Cu2+Zn
• Only metals that are above
hydrogen in the list will react
with H+(aq) and thus
chemically dissolve in acid.
• Copper, silver, and mercury
may be dissolved in
HNO3(aq). However this is
due to the oxidation number
of N in the ion (N is +5).
• Platinum and gold may be
dissolved in a mixtureAtoomfs,
HNO3(aq) + HCl(aq)Molecules,
and Ions
Practice Problem…
• Predict the outcome:
 a) Al(s) + Pb2+(aq)
 b) Mn(s) + CH3COOH(aq)
 c) Hg(l) + H2SO4(aq)
Atoms,
Molecules,
and Ions
Lecture Problem
25.00 mL of a solution of oxalic acid (H2C2O4) is titrated
with 0.1000 M NaOH(aq) until all acidic hydrogens are
neutralized. The solution of acid with some
phenolphthalein is colorless; the solution turns pink
immediately after the addition of 38.56 mL of the base
solution. Calculate the molarity of H2C2O4 in the starting
solution assuming that oxalic acid is diprotic.
Atoms,
Molecules,
and Ions
Solve it yourself…
Problem. A 0.500-g sample of a mixture of NaBr(s) and
Na2CO3(s) was dissolved in water. To precipitate all bromide
and carbonate ions from this solution, 71.5 mL of 0.100 M
AgNO3(aq) were required. Calculate the mass percentage
of sodium bromide in the starting solid mixture.
A: 50% NaBr
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions