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Chapter 7
Reactions in Aqueous Solutions
Chapter 7
Table of Contents
Copyright © Cengage Learning. All rights reserved 2
7.1 Predicting Whether a Reaction Will Occur
7.2 Reactions in Which a Solid Forms
7.3 Describing Reactions in Aqueous Solutions
7.4 Reactions That Form Water: Acids and Bases
7.5 Reactions of Metals with Nonmetals (Oxidation–Reduction)
7.6 Ways to Classify Reactions
7.7 Other Ways to Classify Reactions
Section 7.1
Predicting Whether a Reaction Will Occur
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1. Formation of a solid
2. Formation of water
3. Transfer of electrons
4. Formation of a gas
Four Driving Forces Favor Chemical Change
Section 7.1
Predicting Whether a Reaction Will Occur
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Ukrainian Wolves
Partially charged water molecules act like Ukrainian Wolves in desloving fully charged NaCl ion.
http://www.northland.cc.mn.us/biology/Biolog
y1111/animations/dissolve.swf
Section 7.2
Reactions in Which a Solid Forms
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• A reaction in which a solid forms is called a precipitation reaction. Solid = precipitate
Precipitation
Section 7.2
Reactions in Which a Solid Forms
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• The ions separate and move around independently.• Strong electrolyte – each unit of the substance that
dissolves in water produces separated ions.
What Happens When an Ionic Compound Dissolves in Water?
Section 7.2
Reactions in Which a Solid Forms
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• K2CrO4(aq) + Ba(NO3)2(aq) Products
What Happens When an Ionic Compound Dissolves in Water?
Section 7.2
Reactions in Which a Solid Forms
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• K2CrO4(aq) + Ba(NO3)2(aq) Products
• The mixed solution contains four types of ions: K+, CrO4
2–, Ba2+, and NO3–.
• Determine the possible products from the ions in the reactants. The possible ion combinations are:
How to Decide What Products Form
Section 7.2
Reactions in Which a Solid Forms
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• Decide which is most likely to be the yellow solid formed in the reaction.
• K2CrO4(aq) reactant
• Ba(NO3)2(aq) reactant
• The possible combinations are KNO3 and BaCrO4.
KNO3 white solid
BaCrO4 yellow solid
How to Decide What Products Form
Section 7.2
Reactions in Which a Solid Forms
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Using Solubility Rules
Section 7.2
Reactions in Which a Solid Forms
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Let’s Practice Determining Solubility
Which of the following are solublesoluble in water?
Na2CO3 yes
CaCl2 yes
AgCl no
BaSO4 no
(NH4)2S yes
Cu(OH)2 no
Ba(OH)2
Ca3(PO4)2no
yes
Pb(NO3)2 yes
PbCl2 no
Section 7.2
Reactions in Which a Solid Forms
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Using Solubility Rules
• Predicting Precipitates Soluble solid Insoluble solid Slightly soluble solid
Section 7.2
Reactions in Which a Solid Forms
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1. Write the reactants as they actually exist before any reaction occurs. Remember that when a salt dissolves, its ions separate.
2. Consider the various solids that could form. To do this, simply exchange the anions of the added salts.
3. Use the solubility rules to decide whether a solid forms and, if so, to predict the identity of the solid.
How to Predict Precipitates When Solutions of Two Ionic Compounds Are Mixed
Section 7.2
Reactions in Which a Solid Forms
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Concept Check
Which of the following ions form compounds with Pb2+ that are generally soluble in water?
a) S2–
b) Cl–
c) NO3–
d) SO42–
e) Na+
Section 7.2
Reactions in Which a Solid Forms
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Concept Check
A sodium phosphate solution reacts with a lead(II) nitrate solution. What precipitate, if any, will form?
a) Pb3(PO4)2
b) NaNO3
c) Pb(NO3)2
d) No precipitate will form.
Section 7.2
Reactions in Which a Solid Forms
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Concept Check
Consider a solution with the following ions present:
When all are allowed to react (and there is plenty available of each), how many different solids will form? List them.
Five different solids will form.
PbCl2, PbSO4, Pb3(PO4)2, AgCl, Ag3PO4
- 2+ + + - 2- 3-3 4 4NO , Pb , K , Ag , Cl , SO , PO
Section 7.2
Reactions in Which a Solid Forms
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Net Ionic Equations
AgNO3(aq) + NaCl(aq)
1. Divorce Ag++NO3- + Na++ Cl-
2. Change Partners Ag++NO3- + Na++ Cl- AgCl + NaNO3
3. Soluble? Ag++NO3- + Na++ Cl- AgCl(s) + Na+ NO3
-
4. Cross out Spectator Ions
Ag++ Cl- AgCl(s) 5. Balance
Ag++ Cl- AgCl(s)
Total Ionic Equation
Molecular Equation
Net Ionic Equation
AgCl(s) + NaNO3(aq)
Section 7.2
Reactions in Which a Solid Forms
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Net Ionic Equations
Pb(NO3)2(aq) + NaI(aq)
1. Divorce Pb+2+NO3- + Na++ l-
2. Change Partners Pb+2+NO3- + Na++ l- Pbl2 + NaNO3
3. Soluble? Pb+2+NO3- + Na++ l - Pbl2(s) + Na+ NO3
-
4. Cross out Spectator Ions
Pb+2+ 2 l- Pbl2(s) 5. Balance
Pb+2+ l- Pbl2(s)
Total Ionic Equation
Molecular Equation
Net Ionic Equation
Pbl2(s) + NaNO3(aq)
Section 7.2
Reactions in Which a Solid Forms
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Net Ionic Equations
BaCl2(aq) + Na2SO4(aq)
1. Divorce Ba+2 + Cl- + Na++ SO4-2
2. Change Partners Ba+2 + Cl- + Na++ SO4-2 BaSO4 + NaCl
3. Soluble? Ba+2 + Cl- + Na++ SO4-2 BaSO4(s)+ Na+ + Cl-
4. Cross out Spectator Ions
Ba+2+ SO4-2 BaSO4(s)5. Balance
Ba+2+ SO4-2 BaSO4(s)
Total Ionic Equation
Molecular Equation
Net Ionic Equation
BaSO4(s) + NaCl(aq)
Section 7.3
Describing Reactions in Aqueous Solutions
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1. Molecular Equation Shows the complete formulas of all
reactants and products. It does not give a very clear picture of
what actually occurs in solution.
Types of Equations for Reactions in Aqueous Solutions
Section 7.3
Describing Reactions in Aqueous Solutions
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2. Complete Ionic Equation All strong electrolytes are shown as ions.
Notice: K+ and NO3– ions are present in solution
both before and after the reaction.
Types of Equations for Reactions in Aqueous Solutions
Section 7.3
Describing Reactions in Aqueous Solutions
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2. Complete Ionic Equation Spectator ions – ions which do not
participate directly in a reaction in solution.
Types of Equations for Reactions in Aqueous Solutions
Section 7.3
Describing Reactions in Aqueous Solutions
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3. Net Ionic Equation Only those components of the solution
that undergo a change.
Notice: Spectator ions are not shown in the net ionic equation.
Types of Equations for Reactions in Aqueous Solutions
Section 7.3
Describing Reactions in Aqueous Solutions
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Concept Check
Write the correct molecular equation, complete ionic equation, and net ionic equation for the reaction between cobalt(II) chloride and sodium hydroxide.
Molecular Equation:
CoCl2(aq) + 2NaOH(aq) Co(OH)2(s) + 2NaCl(aq)
Complete Ionic Equation:
Co2+(aq) + 2Cl(aq) + 2Na+(aq) + 2OH(aq)
Co(OH)2(s) + 2Na+(aq) + 2Cl(aq)
Net Ionic Equation:
Co2+(aq) + 2OH(aq) Co(OH)2(s)
Section 7.4
Reactions That Form Water: Acids and Bases
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• A strong acid is one in which virtually every molecule dissociates (ionizes) in water to an H+ ion and an anion.
Arrhenius Acids and Bases
Section 7.4
Reactions That Form Water: Acids and Bases
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Strong Acids Behave as Strong Electrolytes
Section 7.4
Reactions That Form Water: Acids and Bases
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• A strong base is a metal hydroxide that is completely soluble in water, giving separate OH ions and cations. Most common examples: NaOH and KOH
Arrhenius Acids and Bases
Section 7.4
Reactions That Form Water: Acids and Bases
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• The products of the reaction of a strong acid and a strong base are water and a salt. Salt Ionic compound
• Net ionic equation H+(aq) + OH−(aq) H2O(l)
• Reaction of H+ and OH− is called an acid-base reaction. H+ acidic ion OH− basic ion
Arrhenius Acids and Bases
Section 7.4
Reactions That Form Water: Acids and Bases
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1. The common strong acids are aqueous solutions of HCl, HNO3, and H2SO4.
2. A strong acid is a substance that completely dissociates (ionizes) in water (into H+ ions and anions).
3. A strong base is a metal hydroxide compound that is very soluble in water (and dissociates into OH– ions and cations).
Summary of Strong Acids and Strong Bases
Section 7.4
Reactions That Form Water: Acids and Bases
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4. The net ionic equation for the reaction of a strong acid and a strong base is always the same: it shows the production of water.
5. In the reaction of a strong acid and a strong base, one product is always water and the other is always an ionic compound called a salt, which remains dissolved in the water. This salt can be obtained as a solid by evaporating the water.
Summary of Strong Acids and Strong Bases
Section 7.4
Reactions That Form Water: Acids and Bases
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6. The reaction of H+ and OH– is often called an acid-base reaction, where H+ is the acidic ion and OH– is the basic ion.
Summary of Strong Acids and Strong Bases
Section 7.4
Reactions That Form Water: Acids and Bases
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Concept Check
The net ionic equation for the reaction of HNO3 and LiOH is
a) H+ + NO3– + LiOH → H2O + LiNO3
b) HNO3 + LiOH → H2O + LiNO3
c) H+ + OH– → H2O
d) Li+ + NO3– → LiNO3
Section 7.5
Reactions of Metals with Nonmetals (Oxidation–Reduction)
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• Reactions between metals and nonmetals involve a transfer of electrons from the metal to the nonmetal.
• A reaction that involves a transfer of electrons. 2Mg(s) + O2(g) 2MgO(s)
Oxidation–Reduction Reaction
Section 7.5
Reactions of Metals with Nonmetals (Oxidation–Reduction)
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Concept Check
Which of the following best describes what is happening in the following representation of an oxidation–reduction reaction:
a) Metal Al gains 3 e– and O2 – in Fe2O3 loses these 3e–.
b) Metal Al gains 3 e– and Fe3+ in Fe2O3 loses these 3e–.
c) Metal Al loses 3 e– and O2 – in Fe2O3 gains these 3e–.
d) Metal Al loses 3 e– and Fe3+ in Fe2O3 gains these 3e–.
Section 7.5
Reactions of Metals with Nonmetals (Oxidation–Reduction)
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1. A metal–nonmetal reaction can always be assumed to be an oxidation–reduction reaction, which involves electron transfer.
2. Two nonmetals can also undergo an oxidation–reduction reaction. At this point we can recognize these cases only by looking for O2 as a reactant or product. When two nonmetals react, the compound formed is not ionic.
Characteristics of Oxidation–Reduction Reactions
Section 7.6
Ways to Classify Reactions
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• Formation of a solid• Formation of water• Transfer of electrons• Formation of a gas
Driving Forces for a Reaction
Section 7.6
Ways to Classify Reactions
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• Formation of a solid when two solutions are mixed.
• Notice this is also a double–displacement reaction. AB + CD AD + CB
Precipitation Reaction
Section 7.6
Ways to Classify Reactions
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• Involves an H+ ion that ends up in the product water. H+(aq) + OH−(aq) H2O(l)
HCl(aq) + KOH(aq) H2O(l) + KCl(aq)
Acid–Base Reaction
Section 7.6
Ways to Classify Reactions
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• Transfer of electrons 2Li(s) + F2(g) 2LiF(s)
Oxidation–Reduction Reaction
Section 7.6
Ways to Classify Reactions
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• Oxidation–reduction reaction• Single–replacement reaction
A + BC B + AC
Formation of a Gas
Section 7.7
Other Ways to Classify Reactions
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• Involve oxygen and produce energy (heat) so rapidly that a flame results. CH4(g) + 2O2(g) CO2(g) + 2H2O(g)
Special class of oxidation–reduction reactions.
Combustion Reactions
Section 7.7
Other Ways to Classify Reactions
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• A compound forms from simpler materials. C(s) + O2(g) CO2(g)
Special class of oxidation–reduction reactions.
Synthesis (Combination) Reactions
Section 7.7
Other Ways to Classify Reactions
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• Occurs when a compound is broken down into simpler substances. 2H2O(l) 2H2(g) + O2(g)
Special class of oxidation–reduction reactions.
Decomposition Reactions
Section 7.7
Other Ways to Classify Reactions
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Summary
Section 7.7
Other Ways to Classify Reactions
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Concept Check
The reaction between hydrogen and oxygen to form water
2H2 + O2 → 2H2O
can be classified as a(n) ___________ reaction.
a) oxidation–reduction
b) synthesis
c) combustion
d) All of the above