Aqueous Reactions and
Solution Stoichiometry
Chapter 4 BLB 12th
4.1 General Properties of Aqueous Solutions
 Solution – homogeneous mixture (ch. 13)
 Solvent – dissolving medium; aq-water
 Solute – dissolved substance
Electrolytic Properties
 Electrolyte – a substance whose aqueous
solution contains ions; conducts electricity
 Nonelectrolyte – substance that does not
form ions in solution
Aqueous Solutions, cont.
Ionic Compounds in Water
 Ionic solids dissociate (or ionize) into ions
as they dissolve.
 hydration – process of dissolving an ionic
substance in water
 solvation – dissolving in any solvent;
dissolution
Why? Water is polar.
Polarity of molecules
 Electrons are shared
unequally.
 Results in partial
charges (δ), and a…
 Dipole moment
Hydration of NaCl(s)
How many ions does an ionic compound
produce when it dissociates?
KCl,
MgCl2, or
K2SO4?
Aqueous Solutions, cont.
Molecular Compounds in Water
 nonelectrolytes – contain only molecules
(no ions); do not dissociate; do not
conduct electricity; may dissolve in water
 Most molecular compounds are
nonelectrolytes.
 Some may have strong interaction with
water (alcohols).
 Some may dissociate (acids).
Methanol (CH3OH) in water
Aqueous Solutions, cont.
Strong and weak electrolytes – depend on
the extent of dissociation
 Strong – completely dissociate into ions
- all water-soluble ionic compounds, strong
acids & bases
 Weak – remain mostly as neutral molecules
and produce very few ions; establish chemical
equilibrium
- weak acids (like acetic acid) and weak bases
(like amines); water
Note: strong doesn’t mean soluble and vv.
4.2 Precipitation Reactions
 Marked by the formation of an insoluble
product (precipitate)
 Solubility – amount of solute that can be
dissolved in a given amount of solvent at
a certain temperature; g/100g or g/L or
mol/L
 Insoluble – solubility < 0.01 mol/L
 Solubility Rules – Table 4.1, p. 121
 Metathesis (or exchange) reactions
Note: All common compounds of Group I metals and NH4+ are soluble in water.
Metathesis (or exchange) reactions
Molecular:
BaCl2(aq) + Na2SO4(aq) → 2 NaCl(aq) + BaSO4(s)
Complete ionic:
Net ionic:
Metathesis (or exchange) reactions
Molecular:
NaI(aq) + Pb(NO3)2(aq) →
Complete ionic:
Net ionic:
Metathesis (or exchange) reactions
Molecular:
NaOH(aq) + Co(NO3)2(aq) →
Complete ionic:
Net ionic:
4.3 Acids, Bases, and Neutralization Reactions
 Involve H+
 Acid – H+ donor
Base – H+ acceptor
 Neutralization:
acid + base → salt + water
HCl + NaOH → NaCl + H2O
4.3 Acids, Bases, and Neutralization Reactions
Strong and Weak
 Strong – completely dissociate
 Weak – only partially ionize
 Neutralization:
acid + base → salt + water
HCl + NaOH → NaCl + H2O
4.4 Oxidation-Reduction (Redox) Reactions
 Involve transfer of e¯
 Oxidation – loss of e¯
Reduction – gain of e¯
 Oxidation number – a “charge” assigned
to an atom to keep track of electrons
transferred during redox
 Displacement reaction – ion in solution is
replaced through oxidation of an
element.
4.5 Concentrations of Solutions
 Molarity (M) – mole solute/L solution
M • V = mol
 Dilution – adding solvent to decrease
concentration
M1V1 = M2V2
mol1 = mol2; only volume changes
Calculate the concentration (in M) if 2.50 g
(NH4)2SO4 is dissolved in enough water to form
250 mL of solution.
How many grams of K2Cr2O7 are needed to
make 50.0 mL of 0.850 M solution?
Ion Concentration: 0.850 M K2Cr2O7
 Concentration (M) of Cr2O72-?
 Concentration (M) of K+?
What volume (in mL) of 6.0 M HNO3 is
needed to make 250 mL of 1.0 M HNO3?
4.6 Solution Stoichiometry and Chemical Analysis
 Use M and volume to obtain moles
 Titration – process used to determine the
concentration of a solution (p. 145 ff)
 Standard solution – one of precisely known
concentration
 Analyte – solution of unknown concentration
Stoichiometry Overview, p. 144