1. Chapter 4 Reactions in Aqueous Solution
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2. Oxidation–Reduction (Redox)
Oxidation–Reduction (Redox) Reaction: Any process in which electrons are transferred from one substance to another
Oxidation (OIL) is losing electrons
the oxidation number of an element increases,
an element loses electrons,
a compound adds oxygen,
a compound loses hydrogen, or
a half-reaction has electrons as products.
Reduction (GER) is gaining electrons
the oxidation number of an element decreases,
an element gains electrons,
a compound loses oxygen,
a compound gains hydrogen, or
a half-reaction has electrons as reactants.

3. 4.7 Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
1/18/2019
4.7 Acids, Bases, and Neutralization Reactions
Strong acids and strong bases are strong electrolytes.
Weak acids and weak bases are weak electrolytes.
Copyright © 2008 Pearson Prentice Hall, Inc.

4. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
1/18/2019
Acids, Bases, and Neutralization Reactions
These acid-base neutralization reactions are double-replacement reactions just like the precipitation reactions:
MA HOH
HA MOH or
Recall the original definition of an acid-base neutralization written earlier.
While it looks goofy to write water as HOH, it can help students remember where the pieces came from: H (acid) and OH (base). It’s also easier to balance.
MA H2O
HA MOH
Acid
Base
Salt
Water
Copyright © 2008 Pearson Prentice Hall, Inc.

5. Acids
acids are molecular compounds that form H+ when dissolved in water
to indicate the compound is dissolved in water (aq) is written after the formula
not named as acid if not dissolved in water
sour taste
dissolve many metals
like Zn, Fe, Mg; but not Au, Ag, Pt
formula generally starts with H
e.g., HCl, H2SO4

6. Acids Contain H+1 cation and anion in aqueous solution
Binary acids have H+1 cation and nonmetal anion
Oxyacids have H+1 cation and polyatomic anion

7. Naming Binary Acids HCl HCN write a hydro prefix
follow with the nonmetal name
change ending on nonmetal name to –ic
write the word acid at the end of the name
E.g
HCl
HCN

8. Naming Oxyacids
if polyatomic ion name ends in –ate, then change ending to –ic suffix
if polyatomic ion name ends in –ite, then change ending to –ous suffix
write word acid at end of all names
E.g H2SO4 vs. H2SO3

9. Acids, Bases, and Neutralization Reactions
Oxoacids do not begin with hydro.
Hydrochloric acid: HCl
Chloric acid: HClO3
-ate
-ic
-ite
-ous

10. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
1/18/2019
Acids, Bases, and Neutralization Reactions
Acid (Arrhenius): A substance that dissociates in water to produce hydrogen ions, H1+:
H1+(aq) + A1-(aq)
HA(aq)
H1+(aq) + Cl1-(aq)
HCl(aq)
In water, acids produce hydronium ions, H3O1+:
H3O1+(aq) + Cl1-(aq)
HCl(aq) + H2O(aq)
“HA” is a generic chemical formula for an acid.
Hydrogen ions do not exist in water. They are attached to one or more water molecules (often in clusters). For convenience, we’ll write it as hydrogen ion instead of hydronium ion until a later chapter when a deeper look at acids and bases is undertaken.
Copyright © 2008 Pearson Prentice Hall, Inc.

11. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
1/18/2019
Acids, Bases, and Neutralization Reactions
Base (Arrhenius): A substance that dissociates in water to produce hydroxide ions, OH1-:
M1+(aq) + OH1-(aq)
MOH(aq)
Na1+(aq) + OH1-(aq)
NaOH(aq)
Ammonia, commonly called “ammonium hydroxide” is a base:
“M” is shorthand for a metal cation.
It’s really not proper to call “aqueous ammonia” “ammonium hydroxide” even though it’s still commonly labeled as such (ordering chemicals, etc.).
NH41+(aq) + OH1-(aq)
NH3(aq) + H2O(aq)
Copyright © 2008 Pearson Prentice Hall, Inc.

12. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
1/18/2019
Acids, Bases, and Neutralization Reactions
Write the molecular, ionic, and net ionic equations for the reaction of aqueous HBr and aqueous KOH
The order the products are written in is irrelevant.
The products will be water and a salt.
The salt is written using the rules for naming ionic compounds as previously used.
Copyright © 2008 Pearson Prentice Hall, Inc.

13. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
1/18/2019
Acids, Bases, and Neutralization Reactions
Write the molecular, ionic, and net ionic equations for the reaction of aqueous NaOH and aqueous HF.
Copyright © 2008 Pearson Prentice Hall, Inc.

14. Oxidation-Reduction (Redox) Reactions
Chapter 4: Reactions in Aqueous Solution
Oxidation-Reduction (Redox) Reactions
1/18/2019
oxidation occurs when an atom’s oxidation state increases during a reaction
reduction occurs when an atom’s oxidation state decreases during a reaction
Oxidation Number (State): A value which indicates whether an atom is neutral, electron-rich, or electron-poor.
Rules for Assigning Oxidation Numbers
An atom in its elemental state has an oxidation number of 0. Na H2
Br2 S Ne
Oxidation number 0
A monatomic ion has an oxidation number identical to its charge.
Na1+ +1
Ca2+ +2
Al3+ +3
Cl1- -1
O2- -2
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Copyright © 2008 Pearson Prentice Hall, Inc.

15. Oxidation-Reduction (Redox) Reactions
Chapter 4: Reactions in Aqueous Solution
1/18/2019
Oxidation-Reduction (Redox) Reactions
An atom in a polyatomic ion or in a molecular compound usually has the same oxidation number it would have if it were a monatomic ion.
Hydrogen can be either +1 or -1. H O 1- H Ca +1 -2 -1 +2 -1
Oxygen usually has an oxidation number of -2. H O H O O H
H bonded to a nonmetal has an oxidation number of +1.
H bonded to a metal has an oxidation number of -1.
In peroxides, O22-, oxygen has an oxidation number of -1. +1 -2 +1 +1 -1 -1 +1
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Copyright © 2008 Pearson Prentice Hall, Inc.

16. Oxidation-Reduction (Redox) Reactions
Chapter 4: Reactions in Aqueous Solution
Oxidation-Reduction (Redox) Reactions
1/18/2019 3.
Halogens usually have an oxidation number of -1. H Cl Cl O +1 -1 +1 -2 +1
The sum of the oxidation numbers is 0 for a neutral compound and is equal to the net charge for a polyatomic ion.
H2SO3
2(+1) + x + 3(-2) = 0 (net charge)
A major exception is when the halogen is bonded to oxygen.
x = +4 +1 x -2
Cr2O72-
2(x) + 7(-2) = -2 (net charge)
x = +6 x -2
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Copyright © 2008 Pearson Prentice Hall, Inc.

17. Example
Determine the oxidation number for each atom in the following compounds/molecules
CO2 CCl4
CoSO4 K2O2
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18. 4.10 – 4.11 Identifying Redox Reactions
Oxidation is the process that occurs when
the oxidation number of an element increases,
an element loses electrons,
a compound adds oxygen,
a compound loses hydrogen, or
a half-reaction has electrons as products.
a reducing agent .
2Fe2
3O2(g) +
4Fe(s) O3
(s) +3
oxidation
reduction -2
An “agent” causes something to happen.
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19. 4.10 – 4.11 Identifying Redox Reactions
Reduction is the process that occurs when
the oxidation number of an element decreases,
an element gains electrons,
a compound loses oxygen,
a compound gains hydrogen, or
a half-reaction has electrons as reactants.
an oxidizing agent
2Fe2
3O2(g) +
4Fe(s) O3
(s) +3
oxidation
reduction -2
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20. Types of Redox reaction
Single Displacement
Zn(s) + CuSO4(aq)  ZnSO4(aq) + Cu(s)
Combustion
Reaction of nonmetal and metal
C3H8(g) + O2(g)  CO2(s) + H2O(g)
2 Na(s) + Cl2(g)  2 NaCl(s)
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21. Writing the half reactions
We generally split the redox reaction into two separate half- reactions—a reaction just involving oxidation or reduction.
The oxidation half-reaction has electrons as products.
The reduction half-reaction has electrons as reactants.
Example: Identify which reactant is oxidized and reduced. Then write the half oxidation and reduction reactions for
2Cs(s) F2(g)  2CsF(s)
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22. Writing Oxidation and Reduction Reactions
Write the separate half oxidation and reduction reactions for the following equation.
2Mg(s) O2(g) MgO(s)
3 Na(l) + AlCl3(l)  3 NaCl(l) + Al(l)
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23. Single Displacement and The Activity Series of the Elements
Cu2+(aq) + 2Ag(s)
Cu(s) + 2Ag+(aq)
Which one of these reactions will occur?
2Ag+(aq) + Cu(s)
2Ag(s) + Cu2+(aq)
This is a nice one to do as a demonstration. Place a coil of copper wire in a solution of silver nitrate at the beginning of lecture or lab and show it to the students. Show it again at the end of the period.
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24. How to predict redox reaction?
Elements that are higher up in the table are more likely to be oxidized.
Thus, any element higher in the activity series will reduce the ion of any element lower in the activity series.
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25. Examples
Predict the product of the redox reactions below. If no reaction occurs then write N.R
HCl(aq) + Zn(s) 
Mg(NO3)2(aq) + Cu(s) 
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26. 18.1 Balancing Redox Reaction using half equation in an Acidic Solution
1. Assign oxidation numbers to each atom from the given unbalanced equation
2. Split the equation into half-reaction
3. Complete and balance each half reaction
Balance all atoms except O and H
Balance oxygen atoms by adding H2O to one side of the equation
Balance hydrogen atoms by adding H+ ions to one side of the equation
Balance the number of electrons being transferred
4. Combine the half-reaction to obtained the final balanced equation
The electrons must be cancelled
Simplify the equation by reducing coefficients and canceling repeated species
After you’re done, double check your balanced equation
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27. Example Balance the following net ionic equation in acidic solution:
I1-(aq) + Cr2O72-(aq)  Cr3+(aq) + IO31-(aq)
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28. Example
Balance the following net-ionic equation by the half-reaction method.
Cu(s) + NO3-(aq)  Cu2+(aq) + NO2(g) Acidic condition
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29. Balancing Redox Reaction using half equation in an Acidic Solution
Additional steps for balancing equations in basic solution
Follow all steps from the acidic solution ( 1 4)
Add the desired number of –OH react with H+ ions in the reaction; add to both side of the reaction. This is a neutralization step
Simplify the equation by noting that H+ combines with –OH to give H2O
Cancel any repeating H2O and –OH ions and reduce reaction to the lowest coefficients
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30. Example
Balance the following net ionic equation in basic solution: MnO41-(aq) + Br1-(aq)  MnO2(s) + BrO31-(aq)
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