Aqueous Solutions
Ionic Reactions
• General Rules for dissolution (dissociation) of
ionic compounds
– Only 1 cation and 1 anion are formed
– Monoatomic ions = subscripts become coefficients
for the ions
– Polyatomic ions = only subscripts outside of
parentheses become coefficients
– Charges of all ions must add up to zero (because
compounds are neutral
Examples of Ionic Compounds
dissolving in water
• NaBr (s)  Na+(aq) + Br- (aq)
• Cr(NO3)3 (s)  Cr3+ (aq) + 3 NO3- (aq)
Practice
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K2S (s) 
FeCl3 (s) 
MgBr2 (s) 
AlCl3 (s) 
Na2Cr2O7 (s) 
(NH4)2S (s) 
K3PO4 (s) 
Answers
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K2S (s)  2 K+ (aq) + S2- (aq)
FeCl3 (s)  Fe3+ (aq) + 3 Cl- (aq)
MgBr2 (s)  Mg2+ (aq) + 2 Br- (aq)
AlCl3 (s)  Al3+ (aq) + 3 Cl- (aq)
Na2Cr2O7 (s)  2 Na+ (aq) + Cr2O72- (aq)
(NH4)2S (s)  2 NH4+ (aq) + S2- (aq)
K3PO4 (s)  3 K+ (aq) + PO43- (aq)
Will it dissolve in water?
• Soluble: Alkali metals, NH4+, ClO3-, ClO4-,
acetates, NO3-, and strong acids
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• Strong Acids = HCl, HBr, HI, HNO3, H2SO4,
HClO3, HClO4
• All other acids are weak
Will it dissolve in water?
Sometimes Soluble:
• Cl-, Br-, I- except with Ag+, Hg22+, and Pb2+
• Sulfate except with Hg22+, Pb2+, Ca2+, and Ba2+
Will it dissolve
Insoluble:
• CO32-, CrO42-,Cr2O72-, PO43-, P3- except with
Alkali Metals and ammonium
• S2- except with Alkali Metals, Alkaline Earth
Metals and ammonium
• OH- and O2-except with Alkali Metals and
ammonium (slightly soluble with Ca2+, Sr2+,
and Ba2+)
Will a rxn occur?
• Chemical Driving Force
1. Formation of water is the strongest driving force
2. Formation of a precipitate (insoluble compound)
3. Formation of a covalent compound. Many of
these are organic acids or gases
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H2CO3 (aq)  CO2 (g) + H2O (l)
H2SO3(aq)  SO2 (g) + H2O (l)
NH4OH  NH3 (g) + H2O (l)
H2S (aq)  H2S (g)
Practice: Formation of water
• HCl (aq) + NaOH (aq) 
• CaO (s) + 2 HCl (aq) 
Practice: Predicting Products
Solubility Rules
• Always Soluble: Alkali
metals, NH4+, ClO3-, ClO4-,
acetates, NO3-, and strong
acids
• Cl-, Br-, I- except with Ag+, Hg22+, and
Pb2+
Practice Reactions
• KCl + Pb(NO3)2 
Practice: Predicting Product
Solubility Rules
• Always Soluble: Alkali
metals, NH4+, ClO3-, ClO4-,
acetates, NO3-, and strong
acids
• Sulfate except with Ag+, Hg22+, Pb2+,
Ca2+, Sr2+, and Ba2+
Practice Reaction
• Na2SO4 + Ba(NO3)2 
Practice: Formation of a Gas
Gases From Aqueous Soln
Practice Reaction
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• K2SO3 + HNO3 
H2CO3 (aq)  CO2 (g) + H2O (l)
H2SO3(aq)  SO2 (g) + H2O (l)
NH4OH  NH3 (g) + H2O (l)
H2S (aq)  H2S (g)
Practice: Formation of a Gas
Gases from Aqueous Soln:
Practice Reaction:
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• HCl + CaCO3 
H2CO3 (aq)  CO2 (g) + H2O (l)
H2SO3(aq)  SO2 (g) + H2O (l)
NH4OH  NH3 (g) + H2O (l)
H2S (aq)  H2S (g)
Equations
• Molecular Equation = show chemical formulas
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
Equations
• (Complete) Ionic Equation =
– show ions for strong electrolytes
– insoluble compounds (precipitates), gases, and
covalent compounds are written as molecules
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)  Na+(aq) + Cl-(aq) + H2O (l)
Equations
• Net Ionic Equation = Only show substances that
are not present on both reactant and product sides.
• Ex: (Complete) Ionic Equation
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)  Na+(aq) + Cl-(aq) + H2O (l)
• Ex: Net Ionic Equation
H+(aq) + OH-(aq)  H2O (l)
Net Ionic Equations
• Allows chemists to identify active components
of the reaction. Ions not included are
considered “spectator ions”
H+(aq) + OH-(aq)  H2O (l)
• So Na+ and Cl- are spectator ions
Net Ionic Equations
• If all ions cancel on reactant and products
side, then there is no driving force and
therefore no reaction will occur
• Ex: Will potassium chloride and sodium
nitrate react?
Will potassium chloride and sodium
nitrate react?
• Molecular Equation
KCl (aq) + NaNO3 (aq)  NaCl (aq) + KNO3 (aq
Will potassium chloride and sodium
nitrate react?
• Molecular Equation
KCl (aq) + NaNO3 (aq)  NaCl (aq) + KNO3 (aq)
• (Complete) Ionic Equation
K+(aq) + Cl-(aq) + Na+(aq) + NO3-(aq)  Na+(aq) + Cl-(aq) + K+(aq) + NO3-(aq)
Will A Reaction Occur?
• Potassium sulfate is mixed with Barium nitrate
Potassium Sulfate with Barium Nitrate
K2SO4(aq) + Ba(NO3)2(aq)  BaSO4(s) + 2 KNO3 (aq)
Potassium Sulfate with Barium Nitrate
K2SO4(aq) + Ba(NO3)2(aq)  BaSO4(s) + 2 KNO3 (aq)
2K+(aq) + SO42-(aq) + Ba2+(aq) + 2NO3-(aq) 
BaSO4(s) + 2K+(aq) + 2NO3-(aq)
Potassium Sulfate with Barium Nitrate
2K+(aq) + SO42-(aq) + Ba2+(aq) + 2NO3-(aq) 
BaSO4(s) + 2K+(aq) + 2NO3-(aq)
Net Ionic Equation:
SO42-(aq) + Ba2+(aq)  BaSO4(s)