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Chang, 8th Edition, Chapter 4, Worksheet #1
S. B. Piepho, Fall 2005
Types of Chemical Reactions
One skill that chemists learn over time is that of writing and balancing equations. The first
task is deciding what type of reaction is taking place. In this chapter we study three types:
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Precipitation Reactions: In these reactions two soluble salts usually react to form to an
insoluble salt (the precipitate!) and a soluble salt. The cations of the reacting salts exchange
anions. See Chang, Table 4.2, p. 119 for solubility guidelines.
Acid-Base Reactions: Most commonly an acid of the type HX or H2X reacts with a basic
hydroxide to form a salt plus water. Alternatively, the acid may react with ammonia (NH3) to
form an ammonium salt (but no water). These are proton transfer reactions in which H+ (the
proton) is transferred from the acid to the base.
Oxidation-Reduction Reactions: These are reactions in which one type of atom increases in
oxidation number (is oxidized) and another type of atom decreases in oxidation number (is
reduced). A large number of oxidation-reduction (redox) reactions contain one or more
reactants or products, which are pure elements.
Note that hydroxides can react with acids in acid-base reactions, and also with other salts in
precipitation reactions.
Writing Balanced Ionic Equations
The first step in writing a balanced equation is predicting the products of the reaction as
discussed above. Then the steps below are completed in sequence:
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Balance the Molecular Equation: In the “molecular” equation, nothing is broken up into
ions. Salt formulas are written so that the cation charges exactly balance out the anion
charges so that the salt is neutral. Then the equation is balanced for atoms.
Balance the Total Ionic Equation: The first step in writing an ionic equation is to decide
what species should be broken up into ions. The rules below should help!
Break up into Ions
Strong Acids. HCl, HBr, HI, HNO3, HClO4, and
H2SO4 are the most common examples; assume
other acids are weak.
Strong Bases. NaOH, KOH, or Ba(OH)2 are the
most common examples; assume other bases are
weak.
Soluble Salts. Salts of the alkali metals, salts
containing the NH4+ ion, the NO3- ion, and other
salts as specified in Chang, Table 4.2, p. 119.
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Do NOT break up! Leave “as is”!
Weak Acids. Nearly all acids are
weak.
Weak Bases. Nearly all bases are
weak.
Insoluble Salts. Most salts are
insoluble.
Non-electrolytes or Weak
Electrolytes. Examples include H2O,
gases, pure elements, hydrocarbons,
and alcohols.
Balance the Net Ionic Equation: Identify all spectator ions: these are ions that are identical
on both sides of the balanced total ionic equation. Remove the spectator ions from the
equation. What remains is the net ionic equation. Finally, simplify the stoichiometric
coefficients if all of them are divisible by a common factor.
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Chang, 8th Edition, Chapter 4, Worksheet #1
S. B. Piepho, Fall 2005
If all the ions are spectator ions so that nothing is left for your net ionic equation, no reaction
has taken place!
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Exercises
For each of the following reactions, complete the chart. Be sure to balance all of your
equations.
1. Mg(OH)2(s) + HCl(aq)
(a) Reaction type:
Formulas of Products Formed:
(b) Molecular Equation
(c) Total Ionic Equation
(d) Net Ionic Equation
Answer to 1.(d): Mg(OH)2(s) + 2 H+(aq)  Mg2+(aq) + 2 H2O(l)
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2. AgNO3(aq) + K2Cr2O7(aq)
(a) Reaction type:
Formulas of Products Formed:
(b) Molecular Equation
(c) Total Ionic Equation
(d) Net Ionic Equation
Answer to 2.(d): 2 Ag+(aq) + Cr2O72-(aq)  Ag2Cr2O7(s)
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3. NH3(aq) + HC2H3O2(aq)
(or CH3COOH)
(a) Reaction type:
Formulas of Products Formed:
(b) Molecular Equation
(c) Total Ionic Equation
(d) Net Ionic Equation
Answer to 3.(d): NH3 + HC2H3O2  NH4+(aq) + C2H3O2-(aq)
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4. NaOH(aq) + H2SO4(aq)
(a) Reaction type:
Formulas of Products Formed:
(b) Molecular Equation
(c) Total Ionic Equation
(d) Net Ionic Equation
Answer to 4.(d): OH-(aq) + H+(aq)  H2O(l) (obtain this after all coefficients have been divided by
2)
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Chang, 8th Edition, Chapter 4, Worksheet #1
S. B. Piepho, Fall 2005
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5. H2S(aq) + Ba(OH)2(aq)
(a) Reaction type:
Formulas of Products Formed:
(b) Molecular Equation
(c) Total Ionic Equation
(d) Net Ionic Equation
Answer to 5.(d):
H2S(aq) + Ba2+(aq) + 2 OH-(aq) 
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BaS(s) + 2 H2O(l)