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Chapter 4 Aqueous Reactions and Solution Stoichiometry

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Title: Chapter 4 Aqueous Reactions and Solution Stoichiometry


1
Chapter 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.

2
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?

3
Solutions
  • Homogeneous mixtures of two or more pure
    substances.
  • The solvent is present in greatest abundance.
  • All other substances are solutes.

4
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.

5
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.
6
Electrolytes and Nonelectrolytes
  • Soluble ionic compounds tend to be electrolytes.

7
Electrolytes and Nonelectrolytes
  • Molecular compounds tend to be nonelectrolytes,
    except for acids and bases.

8
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9
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 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.
10
Electrolytes
  • A strong electrolyte dissociates completely when
    dissolved in water.
  • A weak electrolyte only dissociates partially
    when dissolved in water.

11
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12
Strong Electrolytes Are
  • Strong acids

13
Strong Electrolytes Are
  • Strong acids
  • Strong bases

14
Strong Electrolytes Are
  • Strong acids
  • Strong bases
  • Soluble ionic salts

15
Precipitation Reactions
  • When one mixes ions that form compounds that are
    insoluble (as could be predicted by the
    solubility guidelines), a precipitate is formed.

16
Metathesis (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)

17
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)

18
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)

19
AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)
How did we know that silver chloride was a
solid??? We checked the solubility table.
20
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21
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)

22
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

23
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.

24
Molecular Equation
  • The molecular equation lists the reactants and
    products in their molecular form.
  • AgNO3 (aq) KCl (aq) ?? AgCl (s) KNO3 (aq)

25
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)

26
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)

27
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)

28
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 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)

29
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.

30
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)

31
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.

32
Acids
  • Substances that increase the concentration of H
    when dissolved in water (Arrhenius).
  • Proton donors (BrønstedLowry).

33
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.
34
Bases
  • Substances that increase the concentration of OH-
    when dissolved in water (Arrhenius).
  • Proton acceptors (BrønstedLowry).

35
Bases
  • The strong bases are the soluble salts of
    hydroxide ion
  • Alkali metals
  • Calcium
  • Strontium
  • Barium

36
Acid-Base Reactions
  • In an acid-base reaction, the acid donates a
    proton (H) to the base.

37
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)

38
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)

39
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)
40
Neutralization ReactionsWhat does this have to
do with you???
  • What happens when you have a stomach ache?
  • What do you do about it?
  • Why?

41
Neutralization 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)

42
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?

43
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)

44
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)

45
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)

46
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)

47
Oxidation-Reduction Reactions
  • One cannot occur without the other.

48
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.

49
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.

50
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.

51
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, however, most notably in
    oxyanions.

52
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.

53
Oxidation 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

55
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)

56
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

57
Which 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)

58
Which 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

59
Displacement Reactionsa.k.a. Single Replacement
Reactions
  • In displacement reactions, ions oxidize an
    element.
  • The ions, then, are reduced.

60
Displacement Reactions
  • In this reaction,
  • silver ions oxidize
  • copper metal.
  • Cu (s) 2 Ag (aq) ?? Cu2 (aq) 2 Ag (s)

61
Displacement Reactions
  • The reverse reaction,
  • however, does not
  • occur.
  • Cu2 (aq) 2 Ag (s) ?? Cu (s) 2 Ag (aq)

x
62
Activity Series
63
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)

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.

65
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.

66
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?

67
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

68
Dilution
M1V1 M2V2
69
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?

70
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

71
Using 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)

72
Using 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)

73
Titration
  • The analytical technique in which one can
    calculate the concentration of a solute in a
    solution.

74
Titration
75
Titration 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)

76
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

77
Courtesy of http//www.siraze.net/chemistry/sezenn
ur/subjects/comics/comics01.htm
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