Chapter 14: Compounds in Aqueous Solutions:
Dissociation: Separation of ions that occurs when an ionic compound dissolves.
EX;
H2O
H2O
NaCl (s)  Na+ (aq) + Cl-(aq)
CaCl2 (s)  Ca2+ (aq) + 2Cl-(aq)
1 f.u.
1 f.u.
1 f.u.
1 f.u.
1 f.u.
2 f.u.
1 mole
1 mole
1 mole
1 mole
1 mole
2 mole
When ionic compounds dissolve in water their ions are hydrated by water
molecules as they dissociate (separate from one another). Assume 100% dissociation for
all ionic compounds.
Problems:
1. Write the equation for the dissolution of magnesium chlorate in water. How
many moles of ions are produced for every 1 mol of magnesium chlorate
dissolved?
2. Write the equation for the dissolution of NH4NO3 in water. How many moles
of each type of ion are produced if 3.5 mol of NH4NO3 dissolved? How
many total moles produced?
3. An aqueous solution is analyzed and found to contain potassium ions and
sulfite ions. Write the equation for the dissolution of the salt that produced
this solution. If the solution contains 0.50 mol of potassium ions, how many
moles of sulfite ions are present?
Precipitation Reactions:
No ionic compound is entirely insoluble in water. Some ionic compounds are just
considered insoluble because their solubility is less than 0.1 g/100g water.
SOLUBILITY RULES:
1. If insoluble, dissociation equations cannot be written.
2. Useful in predicting what will happen if solutions of 2 different soluble
compounds are mixed.
If produces insoluble compound = double replacement reaction & precipitate
(attraction between ions is greater than attraction between ions & water)
Are the following soluble or insoluble?
a. KCl
c. AgCl
e. Ca3(PO4)2
b. NaNO3
d. BaSO4
f. Pb(ClO3)2
Net ionic equations: includes only those compounds and ions that undergo a chemical
change in a reaction in an aqueous solution.