1. Chemical Quantities and Aqueous Reactions
Chapter 4
Chemical Quantities and Aqueous Reactions

2. What Happens When a Solute Dissolves?
there are attractive forces between the solute particles holding them together
there are also attractive forces between the solvent molecules
when we mix the solute with the solvent, there are attractive forces between the solute particles and the solvent molecules
if the attractions between solute and solvent are strong enough, the solute will dissolve

3. Salt vs. Sugar Dissolved in Water
molecular compounds do not dissociate when they dissolve
ionic compounds dissociate into ions when they dissolve

4. Electrolytes and Nonelectrolytes
materials that dissolve in water to form a solution that will conduct electricity are called electrolytes
materials that dissolve in water to form a solution that will not conduct electricity are called nonelectrolytes

5. Electrolytes in Aqueous Solution
Chapter 4: Reactions in Aqueous Solution
Electrolytes in Aqueous Solution
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Strong Electrolytes: Compounds that dissociate to a large extent into ions when dissolved in water.
KCl(aq)
K1+(aq) + Cl1-(aq)
Weak Electrolytes: Compounds that dissociate to a small extent into ions when dissolved in water.
H1+(aq) + CH3CO21-(aq)
CH3CO2H(aq)
For a 0.10 M solution, KCl is approximately 98% dissociated while CH3CO2H (acetic acid) is a little more than 1% dissociated.
The size of the arrows indicate which side of the chemical equation the equilibrium lies on.
The use of the equilibrium arrows is minimal until later chapters on kinetics and chemical equilibrium.
Nonelectrolytes: Substances which do not produce ions in aqueous solutions.
H2O
C12H22O11(aq)
C12H22O11(s)
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6. HCl(aq)  H+(aq) + Cl-(aq)
Acids
acids are molecular compounds that ionize when they dissolve in water
the molecules are pulled apart by their attraction for the water
when acids ionize, they form H+ cations and anions
the percentage of molecules that ionize varies from one acid to another
acids that ionize virtually 100% are called strong acids
HCl(aq)  H+(aq) + Cl-(aq)
acids that only ionize a small percentage are called weak acids
HF(aq) H+(aq) + F-(aq)

7. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
5/29/2018
Acids, Bases, and Neutralization Reactions
Strong acids and strong bases are strong electrolytes.
Weak acids and weak bases are weak electrolytes.
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8. Solubility of Ionic Compounds
compounds that dissolve in a solvent are said to be soluble, while those that do not are said to be insoluble
NaCl is soluble in water, AgCl is insoluble in water
the degree of solubility depends on the temperature
even insoluble compounds dissolve, just not enough to be meaningful

9. Precipitation Reactions and Solubility Guidelines
Chemistry: McMurry and Fay, 6th Edition
Chapter 4: Reactions in Aqueous Solution
Precipitation Reactions and Solubility Guidelines
5/29/2018 5:53:57 AM
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10. Precipitation Reaction
Chapter 4: Reactions in Aqueous Solution
Precipitation Reaction
5/29/2018
Precipitation Reactions: Processes in which soluble reactants yield an insoluble solid product that falls out of solution.
NaNO3(aq) + AgCl(s)
AgNO3(aq) + NaCl(aq)
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11. Aqueous Reactions and Net Ionic Equations
Chapter 4: Reactions in Aqueous Solution
Aqueous Reactions and Net Ionic Equations
5/29/2018
Molecular Equation: All substances in the chemical equation are written using their complete formulas as if they were molecules.
NaNO3(aq) + AgCl(s)
AgNO3(aq) + NaCl(aq)
strong electrolytes
indicated as (aq)
soluble
Precipitate
insoluble
Granted, all of the substances in the chemical equation are ionic compounds but it’s common to call this the molecular equation.
Pictures are useful especially with this reaction. Solutions of lead(II) nitrate and potassium iodide are colorless while the precipitate of lead(II) iodide is yellow.
Ionic Equation: All of the strong electrolytes are written as ions.
Ag1+(aq) + NO31- (aq) + Na1+(aq) + Cl1-(aq)
Na1+(aq) + NO31- (aq) + AgCl(s)
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12. Aqueous Reactions and Net Ionic Equations
Chapter 4: Reactions in Aqueous Solution
Aqueous Reactions and Net Ionic Equations
5/29/2018
Spectator Ions: Ions that undergo no change during the reaction and appear on both sides of the reaction arrow.
Ag1+(aq) + NO31- (aq) + Na1+(aq) + Cl1-(aq)
Na1+(aq) + NO31- (aq) + AgCl(s)
Net Ionic Equation: Only the ions undergoing change are shown.
AgCl(s)
Ag+(aq) + Cl1-(aq)
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13. Example
Predict the products and write a balanced molecular equation, ionic equation and net ionic equation for the following reactions:
K2S(aq) + Fe(NO3)2(aq) 
NaCl(aq) +(NH4)2(aq)CO3 

14. Acid-Base Reaction
Acid-Base Neutralization Reactions: Processes in which an acid reacts with a base to yield water plus a salt.
H2O(l) + NaCl(aq)
HCl(aq) + NaOH(aq)
Acid Base  Water + Salt

15. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
Acids, Bases, and Neutralization Reactions
5/29/2018
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.
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16. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
5/29/2018
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)
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17. Acids, Bases, and Neutralization Reactions
Chapter 4: Reactions in Aqueous Solution
Acids, Bases, and Neutralization Reactions
5/29/2018
Write the molecular, ionic, and net ionic equations for the reaction of aqueous H2SO4 and aqueous KOH
Write the molecular, ionic, and net ionic equations for the reaction of aqueous NaOH and aqueous HF.
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.
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18. Titration
A procedure for determining the concentration of a solution by allowing a carefully measured volume to react with a solution of another substance (the standard solution) whose concentration is known.
Titrant: solution that is added from the buret
Equivalence Point: The point at which stoichiometrically equivalent quantities of acid and base have been mixed together.
Endpoint: is the point at which the titration is complete (usually by a sudden color change), as determined by an indicator,
Types of acid-base titration
Strong acid-strong acid
Strong acid-weak acid
Weak acid-strong base
Weak acid – weak base

19. Titration The base solution is the titrant in the burette.
As the base is added to
the acid, the H+ reacts with
the OH– to form water.
But there is still excess
acid present so the color
does not change.
At the titration’s endpoint,
just enough base has been
added to neutralize all the
acid. At this point the
indicator changes color.

20. Example
The titration of mL of HCl solution of unknown concentration requires mL of M NaOH solution to reach the end point. What is the concentration of the unknown HCl solution?
The titration of a 20.0 mL sample of an H2SO4 solution of an unknown concentration requires mL of a 0.158M KOH solution to reach the equivalent point. What is the concentration of the unknown H2SO4 solution?

21. Gas Evolving Reactions
Some reactions form a gas directly from the ion exchange
K2S(aq) + H2SO4(aq)  K2SO4(aq) + H2S(g)
Other reactions form a gas by the decomposition of one of the ion exchange products into a gas and water
K2SO3(aq) + H2SO4(aq)  K2SO4(aq) + H2SO3(aq)
H2SO3  H2O(l) + SO2(g)

22. Compounds that Undergo Gas Evolving Reactions
Reactant
Type
Reacting
With
Ion Exchange
Product
Decom-pose?
Gas
Formed
Example
metalnS,
metal HS
acid
H2S no
K2S(aq) + 2HCl(aq) 
2KCl(aq) + H2S(g)
metalnCO3,
metal HCO3
H2CO3
yes
CO2
K2CO3(aq) + 2HCl(aq) 
2KCl(aq) + CO2(g) + H2O(l)
metalnSO3
metal HSO3
H2SO3
SO2
K2SO3(aq) + 2HCl(aq) 
2KCl(aq) + SO2(g) + H2O(l)
(NH4)nanion
base
NH4OH
NH3
KOH(aq) + NH4Cl(aq) 
KCl(aq) + NH3(g) + H2O(l)

23. Examples
When an aqueous solution of sodium carbonate is added to an aqueous solution of nitric acid, a gas evolves
Write a molecular equation for the gas-evolution that occurs when you mix aqueous hydrobromic acid and aqueous potassium sulfite

24. Oxidation-Reduction (Redox) Reactions
Chapter 4: Reactions in Aqueous Solution
5/29/2018
Oxidation-Reduction (Redox) Reactions
Rusting of iron:
an oxidation of Fe
2Fe2O3(s)
4Fe(s) + 3O2(g)
Manufacture of iron: a reduction of Fe
4Fe(s) + 3CO2(g)
2Fe2O3(s) + 3C(s)
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25. Oxidation-Reduction (Redox) Reactions
Chapter 4: Reactions in Aqueous Solution
Oxidation-Reduction (Redox) Reactions
5/29/2018
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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26. Oxidation-Reduction (Redox) Reactions
Chapter 4: Reactions in Aqueous Solution
5/29/2018
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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27. Oxidation-Reduction (Redox) Reactions
Chapter 4: Reactions in Aqueous Solution
Oxidation-Reduction (Redox) Reactions
5/29/2018 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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28. Example
Determine the oxidation number for each atom in the following compounds/molecules
CO2 CCl4
CoSO4 K2O2

29. Types of Redox reaction
Combustion
Reaction of nonmetal and metal
2 H2(g) + O2(g)  2 H2O(g)
2 Na(s) + Cl2(g)  2 NaCl(s)

30. Identifying Redox Reactions
Chapter 4: Reactions in Aqueous Solution
5/29/2018
Identifying Redox Reactions
Reduction: gaining one or more electron
increasing in oxidation number
 Oxidizing agent
2Fe2
3O2(g) +
4Fe(s) O3
(s) +3
oxidation
reduction -2
Oxidation: losing one or more electrons
decreasing in oxidation number
 Reducing agent
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31. Oxidation and Reduction Another Definition
oxidation occurs when an atom’s oxidation state increases during a reaction
reduction occurs when an atom’s oxidation state decreases during a reaction
CH O2 → CO2 + 2 H2O –
oxidation
reduction

32. Example Identify each of half reactions as
1) oxidation or 2) reduction.
__A. Sn(s) Sn4+(aq) e−
__B. Fe3+(aq) e− Fe2+(aq)
__C. Cl2(g) e− Cl-(aq)

33. Writing Oxidation and Reduction Reactions
Write the separate half oxidation and reduction reactions for the following equation.
2Cs(s) F2(g) CsF(s)
3 Na(l) + AlCl3(l)  3 NaCl(l) + Al(l)

34. Identify the Oxidizing and Reducing Agents in Each of the Following
3 H2S(aq) + 2 NO3– (aq) + 2 H+ (aq)  3 S(s) + 2 NO(g) + 4 H2O(l) MnO2(s) + 4 HBr(aq)  MnBr2(aq)+ Br2 (g)+ 2 H2O(l)

35. Combustion Reactions
Reactions in which O2(g) is a reactant are called combustion reactions
Combustion reactions release lots of energy
Combustion reactions are a subclass of oxidation-reduction reactions
2 C8H18(g) + 25 O2(g)  16 CO2(g) + 18 H2O(g)
Tro, Chemistry: A Molecular Approach

36. Combustion Products Reactant Combustion Product contains C CO2(g)
Reactions in which O2(g) is a reactant are called combustion reactions
Combustion reactions release lots of energy
Combustion reactions are a subclass of oxidation-reduction reactions
to predict the products of a combustion reaction, combine each element in the other reactant with oxygen
Reactant
Combustion Product
contains C
CO2(g)
contains H
H2O(g)
contains S
SO2(g)
contains N
NO(g) or NO2(g)
contains metal
M2On(s)

37. Practice – Complete the Reactions
combustion of C3H7OH(l)
combustion of CH3NH2(g)