Title: Chapter 4 Aqueous Reactions and Solution Stoichiometry
1Chapter 4Aqueous Reactions and Solution
Stoichiometry
Chemistry, The Central Science, 10th
edition Theodore L. Brown H. Eugene LeMay, Jr.
and Bruce E. Bursten
Ch4 Hmwk 7, 8, 11, 15, 19, 23, 25, 27, 29, 31,
37, 39, 41, 45, 47, 51, 53, 59, 63, 67, 69, 75, 96
- John D. Bookstaver
- St. Charles Community College
- St. Peters, MO
- ? 2006, Prentice Hall, Inc.
2Aqueous Reactions and Solution Stoichiometry
- What is aqueous?
- What is an aqueous reaction?
- What are some types of aqueous reactions?
- Why might these be important? Give examples.
- Aqueous reactions cannot take place without
water. What do you already know about water that
will help us understand aqueous reactions?
3Solutions
- Homogeneous mixtures of two or more pure
substances. - The solvent is present in greatest abundance.
- All other substances are solutes.
4Dissociation
- When an ionic substance dissolves in water, the
solvent pulls the individual ions from the
crystal and solvates them. - This process is called dissociation.
5Electrolytes
- Substances that dissociate into ions when
dissolved in water. Example NaCl - A nonelectrolyte may dissolve in water, but it
does not dissociate into ions when it does so.
Example C12H22O11
Notice, solubility does not imply that something
is or is not an electrolyte.
6Electrolytes and Nonelectrolytes
- Soluble ionic compounds tend to be electrolytes.
7Electrolytes and Nonelectrolytes
- Molecular compounds tend to be nonelectrolytes,
except for acids and bases.
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9Solution  Analyze We are asked to associate
the charged spheres in the diagram with ions
present in a solution of an ionic
substance. Plan We examine the ionic substances
given in the problem to determine the relative
numbers and charges of the ions that each
contains. We then correlate these charged ionic
species with the ones shown in the
diagram. Solve The diagram shows twice as many
cations as anions, consistent with the
formulation K2SO4. Check Notice that the total
net charge in the diagram is zero, as it must be
if it is to represent an ionic substance.
10Electrolytes
- A strong electrolyte dissociates completely when
dissolved in water. - A weak electrolyte only dissociates partially
when dissolved in water.
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12Strong Electrolytes Are
13Strong Electrolytes Are
- Strong acids
- Strong bases
14Strong Electrolytes Are
- Strong acids
- Strong bases
- Soluble ionic salts
15Precipitation Reactions
- When one mixes ions that form compounds that are
insoluble (as could be predicted by the
solubility guidelines), a precipitate is formed.
16Metathesis (Exchange) Reactionsa.k.a. Double
Replacement Rxns
- Metathesis comes from a Greek word that means to
transpose
- AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)
17Metathesis (Exchange) Reactions a.k.a. Double
Replacement Rxns
- Metathesis comes from a Greek word that means to
transpose - It appears the ions in the reactant compounds
exchange, or transpose, ions
- AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)
18Metathesis (Exchange) Reactions
- Metathesis comes from a Greek word that means to
transpose - It appears the ions in the reactant compounds
exchange, or transpose, ions
- AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)
19AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)
How did we know that silver chloride was a
solid??? We checked the solubility table.
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21Predict the products of the following reactions
- BaCl2 (aq) K2SO4 (aq)
- Fe2(SO4)3 (aq) LiOH (aq)
- Mg(NO3)2 (aq) CaS (aq)
- NaCl (aq) KNO3 (aq)
22Predict the products of the following reactions
- BaCl2 (aq) K2SO4 (aq)
- ? BaSO4 (s) 2KCl (aq)
- Fe2(SO4)3 (aq) 6LiOH (aq)
- ? 2Fe(OH)3 (s) 3Li2SO4 (aq)
- Mg(NO3)2 (aq) CaS (aq)
- ? MgS (s) Ca(NO3)2 (aq)
- NaCl (aq) KNO3 (aq)
- ? NaNO3 (aq) KCl (aq) or NR
23Solution Chemistry
- It is helpful to pay attention to exactly what
species are present in a reaction mixture (i.e.,
solid, liquid, gas, aqueous solution). - If we are to understand reactivity, we must be
aware of just what is changing during the course
of a reaction.
24Molecular Equation
- The molecular equation lists the reactants and
products in their molecular form.
- AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)
25Ionic Equation
- In the ionic equation all strong electrolytes
(strong acids, strong bases, and soluble ionic
salts) are dissociated into their ions. - This more accurately reflects the species that
are found in the reaction mixture.
- Ag (aq) NO3- (aq) K (aq) Cl- (aq) ??
- AgCl (s) K (aq) NO3- (aq)
26Net Ionic Equation
- To form the net ionic equation, cross out
anything that does not change from the left side
of the equation to the right.
- Ag(aq) NO3-(aq) K(aq) Cl-(aq) ??
- AgCl (s) K(aq) NO3-(aq)
27Net Ionic Equation
- To form the net ionic equation, cross out
anything that does not change from the left side
of the equation to the right. - The only things left in the equation are those
things that change (i.e., react) during the
course of the reaction.
- Ag(aq) Cl-(aq) ?? AgCl (s)
28Net Ionic Equation
- To form the net ionic equation, cross out
anything that does not change from the left side
of the equation to the right. - The only things left in the equation are those
things that change (i.e., react) during the
course of the reaction. - Those things that didnt change (and were deleted
from the net ionic equation) are called spectator
ions.
- Ag(aq) NO3-(aq) K(aq) Cl-(aq) ??
- AgCl (s) K(aq) NO3-(aq)
29Writing Net Ionic Equations
- Write a balanced molecular equation.
- Dissociate all strong electrolytes.
- Cross out anything that remains unchanged from
the left side to the right side of the equation. - Write the net ionic equation with the species
that remain.
30Writing Net Ionic Equations Write the net ionic
equation for each reaction
- Pb(NO3)2 (aq) KI (aq)
- Li2S (aq) BaBr2 (aq)
- NH4Cl (aq) Sr(OH)2 (aq)
31Writing Net Ionic Equations Write the net ionic
equation for each reaction
- Pb(NO3)2 (aq) 2KI (aq)
- ? PbI2 (s) 2K(NO3) (aq)
- Pb2 2I- ? PbI2 (s)
- Li2S (aq) BaBr2 (aq)
- ? LiBr (aq) BaS (aq)
- 2Li (aq) S-2 (aq) Ba2 (aq) 2Br- (aq) ?
2Li (aq) 2Br- (aq) Ba2 (aq) S-2 (aq) - Notice .all spectator ions. They all cancel and
therefore, no reaction occurs. - 2NH4Cl (aq) Sr(OH)2 (aq)
- ? SrCl2 (aq) 2NH4OH (aq)
- 2NH4 (aq) 2Cl- (aq) Sr2 (aq) 2OH- (aq) ?
Sr2 (aq) 2Cl- (aq) 2NH4 (aq) 2OH- (aq) - Notice .all spectator ions. They all cancel and
therefore, no reaction occurs.
32Acids
- Substances that increase the concentration of H
when dissolved in water (Arrhenius). - Proton donors (BrønstedLowry).
33Acids
- There are only seven strong acids
- Hydrochloric (HCl)
- Hydrobromic (HBr)
- Hydroiodic (HI)
- Nitric (HNO3)
- Sulfuric (H2SO4)
- Chloric (HClO3)
- Perchloric (HClO4)
These substances are consider strong acids
because they do not just dissolve in water, they
will completely dissociate.
34Bases
- Substances that increase the concentration of OH-
when dissolved in water (Arrhenius). - Proton acceptors (BrønstedLowry).
35Bases
- The strong bases are the soluble salts of
hydroxide ion - Alkali metals
- Calcium
- Strontium
- Barium
36Acid-Base Reactions
- In an acid-base reaction, the acid donates a
proton (H) to the base.
37Neutralization Reactions
- Generally, when solutions of an acid and a base
are combined, the products are a salt and water.
- HCl (aq) NaOH (aq) ?? NaCl (aq) H2O (l)
38Neutralization Reactions
- When a strong acid reacts with a strong base, the
net ionic equation is
- HCl (aq) NaOH (aq) ?? NaCl (aq) H2O (l)
- H (aq) Cl- (aq) Na (aq) OH-(aq) ??
- Na (aq) Cl- (aq) H2O (l)
39Neutralization Reactions
- When a strong acid reacts with a strong base, the
net ionic equation is
- HCl (aq) NaOH (aq) ?? NaCl (aq) H2O (l)
- H (aq) Cl- (aq) Na (aq) OH-(aq) ??
- Na (aq) Cl- (aq) H2O (l)
- H (aq) Cl- (aq) Na (aq) OH- (aq) ??
- Na (aq) Cl- (aq) H2O (l)
H (aq) OH- (aq) ? H2O (l)
40Neutralization ReactionsWhat does this have to
do with you???
- What happens when you have a stomach ache?
- What do you do about it?
- Why?
41Neutralization ReactionsWhat does this have to
do with you???
- Many antacids contain magnesium hydroxide. It
undergoes a neutralization reaction with stomach
acid. - What acid constitutes the largest quantity of
stomach acid? - Write a net ionic equation for the neutralization
reaction between magnesium hydroxide and
hydrochloric acid. - Mg(OH)2 (s) H (aq) ? Mg2 (aq) H2O (l)
42Neutralization Reactions
- Observe the reaction between Milk of Magnesia,
Mg(OH)2, and HCl. - Can you overdoes on antacid?? What do you think
would happen?
43Gas-Forming Reactions
- These metathesis reactions do not give the
product expected. - The expected product decomposes to give a gaseous
product (CO2 or SO2).
- CaCO3 (s) HCl (aq) ??CaCl2 (aq) CO2 (g)
H2O (l) - NaHCO3 (aq) HBr (aq) ??NaBr (aq) CO2 (g)
H2O (l) - SrSO3 (s) 2 HI (aq) ??SrI2 (aq) SO2 (g) H2O
(l)
44Gas-Forming Reactions
- This reaction gives the predicted product, but
you had better carry it out in the hood, or you
will be very unpopular! - Just as in the previous examples, a gas is formed
as a product of this reaction
- Na2S (aq) H2SO4 (aq) ?? Na2SO4 (aq) H2S (g)
45A Carbonated Beverage is Another Example
- How is a beverage carbonated?
- What happens to the dissolved gas?
- H2O (l) CO2 (g) ? H2CO3 (aq)
- H2O (l) CO2 (g) ? 2H (aq) CO3-2 (aq)
46Oxidation-Reduction Reactions
- An oxidation occurs when an atom or ion loses
electrons. (It becomes more positive) - A reduction occurs when an atom or ion gains
electrons. (It becomes more negative)
47Oxidation-Reduction Reactions
- One cannot occur without the other.
48Oxidation Numbers
- To determine if an oxidation-reduction reaction
has occurred, we assign an oxidation number to
each element in a neutral compound or charged
entity.
49Oxidation Numbers
- Elements in their elemental form have an
oxidation number of 0. - The oxidation number of a monatomic ion is the
same as its charge.
50Oxidation Numbers
- Nonmetals tend to have negative oxidation
numbers, although some are positive in certain
compounds or ions. - Oxygen has an oxidation number of -2, except in
the peroxide ion in which it has an oxidation
number of -1. - Hydrogen is -1 when bonded to a metal, 1 when
bonded to a nonmetal.
51Oxidation Numbers
- Nonmetals tend to have negative oxidation
numbers, although some are positive in certain
compounds or ions. - Fluorine always has an oxidation number of -1.
- The other halogens have an oxidation number of -1
when they are negative they can have positive
oxidation numbers, however, most notably in
oxyanions.
52Oxidation Numbers
- The sum of the oxidation numbers in a neutral
compound is 0. - The sum of the oxidation numbers in a polyatomic
ion is the charge on the ion.
53Oxidation NumbersFind the oxidation numbers for
each of the following species.
- CO32-
- H2S
- S8
- SCl2
- SO42-
- Cr2O72-
54- CO32-
- C 4 and O -2
- H2S
- H 1 and S -2
- S8
- S 0
- SCl2
- S 2 and Cl -1
- SO42-
- S 6 and O -2
- Cr2O72-
- Cr 6 and O -2
55Examine each Reaction below and Identify the
oxidized and reduced reagents
- 2K (s) 2H2O (l) ? 2KOH (aq) H2 (g)
- Fe2O3 (s) 2Al (s) ? 2Fe (l) Al2O3 (s)
- Si (s) 2Cl2 (g) ? SiCl4 (l)
56Examine each Reaction below and Identify the
oxidized and reduced agents
- 2K (s) 2H2O (l) ? 2KOH (aq) H2 (g)
- K (s) ? K (aq), it was oxidized Hydrogen was
reduced in water to form hydrogen gas. - Fe2O3 (s) 2Al (s) ? 2Fe (l) Al2O3 (s)
- Aluminum metal is oxidized iron is reduced
- Si (s) 2Cl2 (g) ? SiCl4 (l)
- Si is oxidized while Cl is reduced
57Which three of the following reactions are
Red-Ox? What is oxidized and what is reduced?
- Zn (s) 2NO3- (aq) 4H (aq) ? Zn2 (aq) 2NO2
(g) 2H2O (l) - Zn(OH)2 (s) H2SO4 (aq) ? ZnSO4 (aq) 2H2O (l)
- Ca (s) 2H2O (l) ? Ca(OH)2 (s) H2 (g)
- 4Fe(OH)2 (s) 2H2O (l) O2 (g) ? 4Fe(OH)3 (aq)
58Which three of the following reactions are
Red-Ox? What is oxidized and what is reduced?
- Zn (s) 2NO3- (aq) 4H (aq) ? Zn2 (aq) 2NO2
(g) 2H2O (l) - Red-ox zinc is oxidized, nitrogen is reduced
- Zn(OH)2 (s) H2SO4 (aq) ? ZnSO4 (aq) 2H2O (l)
- Not Red-ox
- Ca (s) 2H2O (l) ? Ca(OH)2 (s) H2 (g)
- Red-ox calcium is oxidized, hydrogen is reduced
- 4Fe(OH)2 (s) 2H2O (l) O2 (g) ? 4Fe(OH)3 (aq)
- Red-ox Iron is oxdized, oxygen is reduced
59Displacement Reactionsa.k.a. Single Replacement
Reactions
- In displacement reactions, ions oxidize an
element. - The ions, then, are reduced.
60Displacement Reactions
- In this reaction,
- silver ions oxidize
- copper metal.
- Cu (s) 2 Ag (aq) ?? Cu2 (aq) 2 Ag (s)
61Displacement Reactions
- The reverse reaction,
- however, does not
- occur.
- Cu2 (aq) 2 Ag (s) ?? Cu (s) 2 Ag (aq)
x
62Activity Series
63Use the Activity Series to predict the products
of the following reactions. If the reactions
does take place, write the net ionic equation for
the reaction. Lastly, identify the species being
oxidized and reduced.
- Al (s) HBr (aq)
- Fe(s) KI (aq)
- Zn (s) Ni(NO3)2 (aq)
64- 2Al (s) 6HBr (aq)
- ? 2AlBr3 (aq) 3H2 (g)
- 2Al (s) 6H (aq) ? 2Al3 (aq) 3H2(g)
- Aluminum is oxidized and Hydrogen is reduced.
- Fe(s) KI (aq)
- No Reaction
- Zn (s) Ni(NO3)2 (aq)
- ? Zn(NO3)2 (aq) Ni (s)
- Zn (s) Ni2 (aq) ? Zn2 (aq) Ni (s)
- Zinc is oxidized and Nickel is reduced.
65Molarity
- Two solutions can contain the same compounds but
be quite different because the proportions of
those compounds are different. - (For example, it would be much more dangerous to
spill a high concentration of hydrochloric acid
on your hand than a low concentration) - Molarity is one way to measure the concentration
of a solution.
66Mixing a Solution
- How many grams of silver nitrate are required to
make 100 mL of a 0.5 M solution? - How many grams of NaOH are required to make 50
mL of an 8.2 M solution?
67Mixing a Solution
- How many grams of silver nitrate are required to
make 100 mL of a 0.5 M solution? - 9 grams
- How many grams of NaOH are required to make 50.0
mL of an 8.2 M solution? - 16 grams
68Dilution
M1V1 M2V2
69Dilution
- You have 1L of a 1.00 M stock solution of
hydrochloric acid. You need to make 500 mL of a
0.20M solution. How much of the stock solution
is needed? - You need to make 100 mL of 0.50 M nitric acid.
The storage bottle reads 6.0M. How much of the
6.0M nitric acid will you need?
70Dilution
- You have 1L of a 1.00 M stock solution of
hydrochloric acid. You need to make 500 mL of a
0.20M solution. How much of the stock solution
is needed? - 100. mL or 0.100 L
- You need to make 100 mL of 0.50 M nitric acid.
The storage bottle reads 6.0M. How much of the
6.0M nitric acid will you need? - 8.3 mL
71Using Molarities inStoichiometric Calculations
- How many grams of Ca(OH)2 are needed to
neutralize 20.0 mL of a 0.150 M H2SO4 solution? - 0.222 g (see board for work)
72Using Molarities inStoichiometric Calculations
- How many liters of 0.500 M HCl are needed to
react completely with 0.100 mol Pb(NO3)2, forming
the precipitate PbCl2? - 0.400L (see board for work)
73Titration
- The analytical technique in which one can
calculate the concentration of a solute in a
solution.
74Titration
75Titration Example
- A 1.034-g sample of impure oxalic acid (H2C2O4)
is dissolved in water and an acid-base indicator
is added. The sample required 34.47 mL of 0.485
M NaOH to reach the equivalence point. What is
the mass of oxalic acid and what is its mass
percent in the sample? - 0.752 g H2C2O4 and 72.7 H2C2O4
- (see board for work)
76Titration
- A 0.263-g sample of sodium carbonate requires
28.35 mL of aqueous HCl for titration to the
equivalence point. What is the molarity of the
HCl? - 0.175 M HCl
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