Chapter 7: Reactions in aqueous
solutions
Chemistry 1020: Interpretive chemistry
Andy Aspaas, Instructor
Reactions in which a solid forms
• Precipitation: formation of a solid in a chemical
reaction (a precipitation reaction)
• Precipitate: the solid that forms
• Whether a precipitate forms or not depends strongly
on the solubility of that compound (ability of a
compound to dissolve in water)
Process of ionic compounds dissolving in water
• If an ionic compound dissolves in water, its positive
and negative ions separate and move independently
– Strong electrolyte: an ionic compound whose
ions separate completely when dissolved in
water, and therefore conducts electricity
– Molecular substances like sugar are not strong
electrolytes even though they’re soluble in water
• Electrolytes must be made of ions!
Precipitation reactions
• When two strong electrolytes are mixed together, all
the ions are mixed
• Any +/- combinations of ions in the solution can form
products
• To predict possible products of a precipitation
reaction, separate the reactants into their
component ions, and swap partners to form new
products
AgNO3(aq) + KI(aq)  ?
Precipitation reactions
• But simply predicting the products of a precipitation
reaction does not predict whether a visible reaction
will occur or not
• You must determine the solubility of the products
– If all products are soluble in water, no reaction
will have occurred
– If one or more products are insoluble, they are
the precipitate that has formed
Solubility rules
• A “soluble” compound is one which readily and
completely dissolves in water (the ions separate and
disperse)
• An “insoluble” or “slightly soluble” compound is one
which, for the most part, does not dissolve in water
• Solubility rules allow us to predict whether a
compound is soluble or insoluble
Solubility rules
• Predict the solubility:
CaSO4
MgCl2
NaOH
LiOH
CuSO4
AlPO4
AgI
NH4C2H4O4
Using solubility rules to predict precipitation
• Solubility rules can be used to assign phase labels
to all constituents of a reaction
– Insoluble compounds are solid (s)
– Soluble compounds are aqueous (aq)
• If all compounds in a reaction are aqueous, no
reaction has occurred (NR)
Predict the products
NH4Cl + H2SO4 
K3PO4 + AlCl3 
CuSO4 + KOH 
Sodium carbonate and
barium nitrate
Ammonium sulfide and
cobalt(II) chloride
Sodium hydroxide and
iron(III) chloride
Describing aqueous reactions
• Molecular equation: show ionic formulas of all
reactants and products
• Complete ionic equation: any soluble (aq)
compound is shown as its component ions
– Aqueous sodium chloride
• NaCl(aq) in molecular equation
• Na+(aq) + Cl–(aq) in complete ionic equation
– Other compounds (s), (l), or (g) remain as they
would in molecular equation
Net ionic equations
• Spectator ions: ions which do not participate in the
reaction
– Exist as ionic form on both products and
reactants side of the equation
• Net ionic equation: ionic equation with no spectator
ions
Practice writing equations
Write the molecular, complete ionic, and net ionic
equations for the following reactions
Mixture of potassium sulfide and calcium nitrate
Mixture of nickel(II) sulfate and barium chloride