Ch 7 Notes (Part 2)
7.2
Reactions in Which a Solid Forms
1. A solid formed in an aqueous solution of ionic compounds is called a precipitate.
a. Ionic compounds, which consist of a metal bonded to a nonmetal, are collectively known as salts.
b. Solutions of dissolved salts consist of separated cations and anions. Chemists know that separated
ions are present when ionic solids dissolve in water because the solutions become excellent conductors of
electricity. Pure water does not conduct electricity. (See Fig 7.2 in text.)
c. When solutions of dissolved salts are mixed together, the process of solid formation is called
precipitation. A solid forms because some salt products are insoluble in water.
d. The reaction is known as a precipitation (or a double-displacement) reaction.
e. Example: when a solution of potassium chromate is mixed with a solution of barium nitrate a
yellow precipitate forms.
K2CrO4(aq) + Ba(NO3)2(aq)  yellow precipitate
f. What is the composition of the yellow precipitate? How does it form?
2. To answer the above, let’s look at the nature of ionic compounds dissolved in water.
a. Ionic compounds (a metal bonded to a nonmetal) dissolve in water producing separate ions.
b. In the example above, potassium chromate dissolves in water producing potassium ions and
chromate ions:
K2CrO4 
-
Likewise, barium nitrate dissolves to produce barium ions and nitrate ions:
Ba(NO3)2 
c. A more accurate equation shows the ions present when the two solutions are mixed:
2K+(aq) + CrO42-(aq) + Ba2+(aq) + 2NO3-(aq)  products
3. How to determine the formula of a precipitate formed when the two aqueous solutions are mixed?
a. Method 1:
{
}
cation-anion
combinations
cations
{
(1) Determine all possible combinations of products by making a table, as shown below. Put the
cations on one side and the anions across the top. Pair up each cation with each anion.
`
anions
1
2) Discard the possible products that are the same as the reactants. This leaves ____________
and ____________ as possible products. Which one, in fact, is the yellow solid?
3) Use the Solubility Rules handout (or Table 7.1 in text) to determine the solid product.
a) A soluble solid is one that dissolves readily in water
b) An insoluble or slightly soluble solid does not dissolve, or dissolves very little, in water.
c) According to solubility rules, ______________ is insoluble in water, whereas _______________
is soluble. Therefore, the solid product is ___________ and ___________ remains as dissolved ions in
solution. (How can the solid product and dissolved salt be recovered?)
d) Write the balanced molecular equation showing the appropriate states of matter:
K2CrO4(aq) + Ba(NO3)2(aq) 
b. Method 2.
1) A precipitation reaction can also be described in the general form below,
AB
+
K2CrO4(aq)
+

CD
Ba(NO3)2(aq)
AD
+
CB

2). Note that the cations switch anion partners to form the possible products. The potassium ion is
paired with the nitrate anion and the barium cation is paired with the chromate anion to produce the
possible products. The actual product formula is determined by consulting the solubility table.
Summary: Steps for predicting the precipitate product in aqueous reactions.
Step 1: Write reactants as ions.
Step 2: Exchange the anions of the dissolved compounds (salts) to determine possible products.
Step 3: Use solubility rules to determine if a solid forms.
Questions:
1. Use the solubility rules to predict which of the following substances will be soluble or insoluble in
water.
a. PbS
___________
i. ammonium sulfide
________________
b. Mg(OH)2
________________
j. cobalt(III) nitrate
___________
c. Na2SO4
________________
k. cesium
___________
d. (NH4)2S
___________
l. magnesium sulfite
___________
e. BaCO3
________________
m. aluminum nitrate
___________
f. AlPO4
________________
n. tin(II) hydroxide
___________
g. PbCl2
________________
o. manganese(II) iodide
___________
h. Au(NO3)3
________________
p. iron(II) nitrate
___________
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2. Apply what you’ve learned. Write the balanced molecular equation for each reaction below. Show the
appropriate states of matter. Use your solubility table to determine if a precipitate is formed.
Note: if no precipitate is formed, there was no reaction. All you have is a mixture of dissolved ions.

a.
H2SO4(aq)
+
BaCl2(aq)
b.
AgNO3(aq)
+
KCl(aq) 
c.
KNO3(aq)
+
CaCl2(aq)
d.
Aqueous ammonium carbonate reacts with aqueous magnesium sulfate
e.
Aqueous cobalt (III) chloride reacts with aqueous sodium hydroxide
f.
Aqueous copper (II) sulfate reacts with aqueous sodium carbonate

Aswer problem 17 on page 202 and problem 71 on page 205 in your text.
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7.3
Describing Aqueous Reactions
1. The molecular equation for a precipitation reaction shows the complete formulas for all reactants and
products. (Be aware that there are no actual molecules in a precipitation reaction as all compounds
involved are ionic. The term “molecular,” in this context, simply refers to the complete formulas, not the
actual natures of the compounds.)
Example:
2. Molecular equations do not describe what actually occurs in a solution. The complete ionic equation
for the reaction show the actual forms of the reactants and products in solutions.
Example:
3. Those ions not participating in the reaction to produce a product are present on both sides of the
equations are called the spectator ions.
4. The net ionic equation includes only those components (species) that are directly involved in the
reaction. Removing the spectator ions reveals the net ionic equation.
Example:
5. Write the molecular equation, complete ionic equation, net ionic equation, and identify the spectator
ions when the following aqueous solutions are mixed.
a. lead (II) nitrate and sodium sulfate
b. sodium sulfide and copper (II) nitrate
c. sodium carbonate and iron (III) chloride
d. barium nitrate and potassium chloride
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7.4
Reactions that form Water: Acids and Bases
1. An acid is a compound that produces H+ ions (protons) and an anion when dissolved in water.
2. A strong acid is one in which every molecule dissociates to give ions. Since they completely
dissociate they are strong electrolytes
Ex:
3. A base is a compound that produces hydroxide ions (OH-) and a cation when dissolved in water.
4. A strong base is one that completely dissociates into ions when dissolved in water. Strong bases are,
therefore, strong electrolytes.
Ex:
5. When strong acids and strong bases mix, the fundamental chemical change that occurs is when H+
ions combine with OH- ions to form water. The formation of water is the driving force for this reaction.
The cation from the base and the anion from the acid generally remain as a dissolved salt (spectator ions)
or may precipitate out as a solid salt, depending on their solubility. (See Summary chart on page 188.)
6. Every strong acid-strong base reaction produces ______________________________.
Example:
Nitric acid reacts with sodium hydroxide to produce water and a dissolved salt
Molecular equation
HNO3(aq) + NaOH(aq)  H2O(l) + NaNO3(aq)
Complete ionic equation
Spectator ions
Net ionic equation
6. Write the balanced molecular equation, complete ionic equation, net ionic equation, and identify the
spectator ions for the following acid-base reaction:
Aqueous sulfuric acid is mixed with aqueous sodium hydroxide
7. Solve problem 39 (a to d) on page 203. (For problem 39d please note the correct formula for
calcium hydroxide is Ca(OH)2.)
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