Transcript Chapter 4 Aqueous 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
Chapter 4
Aqueous Reactions and
Solution Stoichiometry
John D. Bookstaver
St. Charles Community College
St. Peters, MO
 2006, Prentice Hall, Inc.
Aqueous
Reactions
Aqueous 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?
Aqueous
Reactions
Solutions:
• Homogeneous
mixtures of two or
more pure
substances.
• The solvent is
present in greatest
abundance.
• All other substances
are solutes.
Aqueous
Reactions
Dissociation
• When an ionic
substance dissolves
in water, the solvent
pulls the individual
ions from the crystal
and solvates them.
• This process is called
dissociation.
Aqueous
Reactions
Electrolytes
• 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.
Aqueous
Reactions
Electrolytes and
Nonelectrolytes
Soluble ionic
compounds tend
to be electrolytes.
Aqueous
Reactions
Electrolytes and
Nonelectrolytes
Molecular
compounds tend to
be nonelectrolytes,
except for acids and
bases.
Aqueous
Reactions
SAMPLE EXERCISE 4.1 Relating Relative Numbers of Anions and
Cations to Chemical Formulas
The diagram below represents an aqueous solution of one of the following
compounds: MgCl2 , KCl, or K2SO4. Which solution does it best represent?
Aqueous
Reactions
SAMPLE EXERCISE 4.1 Relating Relative Numbers of Anions and
Cations to Chemical Formulas
The diagram below represents an aqueous solution of one of the following compounds: MgCl 2 , KCl, or K2SO4.
Which solution does it best represent?
Solution
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 K 2SO4.
Aqueous
Check: Notice that the total net charge in the diagram is zero, as it must be if it is to represent an ionic Reactions
substance.
Electrolytes
• A strong electrolyte
dissociates completely
when dissolved in
water.
• A weak electrolyte
only dissociates
partially when
dissolved in water.
Aqueous
Reactions
Aqueous
Reactions
Strong Electrolytes Are…
• Strong acids
Aqueous
Reactions
Strong Electrolytes Are…
• Strong acids
• Strong bases
Aqueous
Reactions
Strong Electrolytes Are…
• Strong acids
• Strong bases
• Soluble ionic salts
Aqueous
Reactions
Precipitation Reactions
When one mixes ions
that form compounds
that are insoluble (as
could be predicted by
the solubility
guidelines), a
precipitate is formed.
Aqueous
Reactions
Metathesis (Exchange) Reactions
a.k.a. Double Replacement Rxns
• Metathesis comes from a Greek word that
means “to transpose”
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
Aqueous
Reactions
Metathesis (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)
Aqueous
Reactions
Metathesis (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)
Aqueous
Reactions
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
How did we know that silver chloride was a solid???
We checked the solubility table.
Aqueous
Reactions
Aqueous
Reactions
Predict 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)
Aqueous
Reactions
Predict 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
Aqueous
Reactions
Solution 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.
Aqueous
Reactions
Molecular Equation
The molecular equation lists the reactants
and products in their molecular form.
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
Aqueous
Reactions
Ionic 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)
Aqueous
Reactions
Net 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)
Aqueous
Reactions
Net 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)
Aqueous
Reactions
Net 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 didn’t 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)
Aqueous
Reactions
Writing Net Ionic Equations
1. Write a balanced molecular equation.
2. Dissociate all strong electrolytes.
3. Cross out anything that remains
unchanged from the left side to the
right side of the equation.
4. Write the net ionic equation with the
species that remain.
Aqueous
Reactions
Writing 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)
Aqueous
Reactions
Writing 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.
Aqueous
Reactions
Acids:
• Substances that
increase the
concentration of H+
when dissolved in
water (Arrhenius).
• Proton donors
(Brønsted–Lowry).
Aqueous
Reactions
Acids
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.
Aqueous
Reactions
Bases:
• Substances that
increase the
concentration of
OH− when dissolved
in water (Arrhenius).
• Proton acceptors
(Brønsted–Lowry).
Aqueous
Reactions
Bases
The strong bases
are the soluble salts
of hydroxide ion:
•
•
•
•
Alkali metals
Calcium
Strontium
Barium
Aqueous
Reactions
Acid-Base Reactions
In an acid-base
reaction, the acid
donates a proton
(H+) to the base.
Aqueous
Reactions
Neutralization 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)
Aqueous
Reactions
Neutralization 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)
Aqueous
Reactions
Neutralization 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)
Aqueous
Reactions
Neutralization Reactions
What does this have to do with you???
What happens when you have a stomach
ache?
What do you do about it?
Why?
Aqueous
Reactions
Neutralization Reactions
What 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)
Aqueous
Reactions
Neutralization Reactions
Observe the
reaction between
Milk of Magnesia,
Mg(OH)2, and HCl.
Can you overdoes
on antacid?? What
do you think would
happen?
Aqueous
Reactions
Gas-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)
Aqueous
Reactions
Gas-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)
Aqueous
Reactions
A 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)
Aqueous
Reactions
Oxidation-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)
Aqueous
Reactions
Oxidation-Reduction Reactions
One cannot occur
without the other.
Aqueous
Reactions
Oxidation 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.
Aqueous
Reactions
Oxidation 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.
Aqueous
Reactions
Oxidation 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.
Aqueous
Reactions
Oxidation 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,
Aqueous
however, most notably in oxyanions.
Reactions
Oxidation 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.
Aqueous
Reactions
Oxidation Numbers
Find the oxidation numbers for each of the
following species.
•
•
•
•
•
•
CO32H 2S
S8
SCl2
SO42Cr2O72Aqueous
Reactions
•
•
•
•
•
•
•
•
•
•
•
•
CO32C = +4 and O = -2
H2S
H = +1 and S = -2
S8
S=0
SCl2
S = +2 and Cl = -1
SO42S = +6 and O = -2
Cr2O72Cr = +6 and O = -2
Aqueous
Reactions
Examine 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)
Aqueous
Reactions
Examine 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
Aqueous
Reactions
Which three of the following reactions are
Red-Ox? What is oxidized and what is
reduced?
Zn (s) + 2NO3- (aq) + 4H+ (aq) → Zn+2 (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)
Aqueous
Reactions
Which three of the following reactions are
Red-Ox? What is oxidized and what is
reduced?
Zn (s) + 2NO3- (aq) + 4H+ (aq) → Zn+2 (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
Aqueous
Reactions
Displacement Reactions
a.k.a. Single Replacement Reactions
• In displacement
reactions, ions
oxidize an element.
• The ions, then, are
reduced.
Aqueous
Reactions
Displacement Reactions
In this reaction,
silver ions oxidize
copper metal.
Cu (s) + 2 Ag+ (aq)  Cu2+ (aq) + 2 Ag (s)
Aqueous
Reactions
Displacement Reactions
The reverse reaction,
however, does not
occur.
x Cu (s) + 2 Ag+ (aq)
Cu2+ (aq) + 2 Ag (s) 
Aqueous
Reactions
Activity Series
Aqueous
Reactions
Use 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)
Aqueous
Reactions
• 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.
Aqueous
Reactions
Molarity
• 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.
Molarity (M) =
moles of solute
volume of solution in liters
Aqueous
Reactions
Mixing 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?
Aqueous
Reactions
Mixing 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
Aqueous
Reactions
Dilution
M1V1 = M2V2
Aqueous
Reactions
Dilution
• 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?
Aqueous
Reactions
Dilution
• 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
Aqueous
Reactions
Using Molarities in
Stoichiometric 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)
Aqueous
Reactions
Using Molarities in
Stoichiometric 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)
Aqueous
Reactions
Titration
The analytical
technique in
which one can
calculate the
concentration of
a solute in a
solution.
Aqueous
Reactions
Titration
Aqueous
Reactions
Titration Example
A 1.034-g sample of impure oxalic acid
(H2C2O4) is dissolved in water and an acidbase 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)
Aqueous
Reactions
Titration
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
Aqueous
Reactions
Courtesy of http://www.siraze.net/chemistry/sezennur/subjects/comics/comics01.htm
Aqueous
Reactions