Stomach Acid & Heartburn The cells that line your stomach
produce hydrochloric acid to kill unwanted bacteria to help break
down food to activate enzymes that break down food Acid Reflux =
stomach acid backs up into the esophagus, irritating tissues, and
causing heartburn Mild cases of heartburn can be cured by
neutralizing the acid in the esophagus swallowing saliva, which
contains bicarbonate ion taking antacids that contain hydroxide
ions and/or carbonate ions Tro, Chemistry: A Molecular Approach,
2/e
Slide 3
Properties of Acids Sour taste React with active metals i.e.,
Al, Zn, Fe, but not Cu, Ag, or Au 2 Al + 6 HCl AlCl 3 + 3 H 2
corrosive React with carbonates, producing CO 2 marble, baking
soda, chalk, limestone CaCO 3 + 2 HCl CaCl 2 + CO 2 + H 2 O Change
color of vegetable dyes blue litmus turns red React with bases to
form ionic salts Tro, Chemistry: A Molecular Approach, 2/e
Slide 4
Common Acids Tro, Chemistry: A Molecular Approach, 2/e
Slide 5
Structures of Acids Binary acids have acid hydrogens attached
to a nonmetal atom HCl, HF Tro, Chemistry: A Molecular Approach,
2/e
Slide 6
Structure of Acids Oxy-acids have hydrogen atoms attached to an
oxygen atom H 2 SO 4, HNO 3 Tro, Chemistry: A Molecular Approach,
2/e
Slide 7
Structure of Acids Carboxylic acids have COOH group HC 2 H 3 O
2, H 3 C 6 H 5 O 7 Only the first H in the formula is acidic the H
is on the COOH Tro, Chemistry: A Molecular Approach, 2/e
Slide 8
Properties of Bases Also known as alkalis Taste bitter
alkaloids = plant product that is alkaline often poisonous
Solutions feel slippery Change color of vegetable dyes different
color than acid red litmus turns blue React with acids to form
ionic salts neutralization Tro, Chemistry: A Molecular Approach,
2/e
Slide 9
Common Bases Tro, Chemistry: A Molecular Approach, 2/e
Slide 10
Structure of Bases Most ionic bases contain OH ions NaOH,
Ca(OH) 2 Some contain CO 3 2 ions CaCO 3 NaHCO 3 Molecular bases
contain structures that react with H + mostly amine groups Tro,
Chemistry: A Molecular Approach, 2/e
Slide 11
Indicators Chemicals that change color depending on the
solutions acidity or basicity Many vegetable dyes are indicators
anthocyanins Litmus from Spanish moss red in acid, blue in base
Phenolphthalein found in laxatives red in base, colorless in acid
Tro, Chemistry: A Molecular Approach, 2/e
Slide 12
Arrhenius Theory Bases dissociate in water to produce OH ions
and cations ionic substances dissociate in water NaOH(aq) Na + (aq)
+ OH (aq ) Acids ionize in water to produce H + ions and anions
because molecular acids are not made of ions, they cannot
dissociate they must be pulled apart, or ionized, by the water
HCl(aq) H + (aq) + Cl (aq ) in formula, ionizable H written in
front HC 2 H 3 O 2 (aq) H + (aq) + C 2 H 3 O 2 (aq) Tro, Chemistry:
A Molecular Approach, 2/e
Slide 13
Arrhenius Theory HCl ionizes in water, producing H + and Cl
ions NaOH dissociates in water, producing Na + and OH ions Tro,
Chemistry: A Molecular Approach, 2/e
Slide 14
Hydronium Ion The H + ions produced by the acid are so reactive
they cannot exist in water H + ions are protons!! Instead, they
react with water molecules to produce complex ions, mainly
hydronium ion, H 3 O + H + + H 2 O H 3 O + there are also minor
amounts of H + with multiple water molecules, H(H 2 O) n + Tro,
Chemistry: A Molecular Approach, 2/e
Slide 15
Arrhenius AcidBase Reactions The H + from the acid combines
with the OH from the base to make a molecule of H 2 O it is often
helpful to think of H 2 O as H-OH The cation from the base combines
with the anion from the acid to make a salt acid + base salt +
water HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) Tro, Chemistry: A
Molecular Approach, 2/e
Slide 16
Problems with Arrhenius Theory Why do molecular substances,
such as NH 3, dissolve in water to form basic solutions even though
they do not contain OH ions? How do some ionic compounds, such as
Na 2 CO 3 or Na 2 O, dissolve in water to form basic solutions even
though they do not contain OH ions? Why do molecular substances,
such as CO 2, dissolve in water to form acidic solutions even
though they do not contain H + ions? How do acidbase reactions take
place outside aqueous solutions? Tro, Chemistry: A Molecular
Approach, 2/e
Slide 17
Another Definition: Brnsted-Lowry Acid-Base Theory Brnsted and
Lowry redefined acids and bases based on what happens in a
reaction. Any reaction that involves H + being transferred from one
molecule to another is an acidbase reaction regardless of whether
it occurs in aqueous solution, or if there is OH present The
Brnsted-Lowry definition includes all reactions that fit the
Arrhenius definition. Many others as well. Tro, Chemistry: A
Molecular Approach, 2/e
Slide 18
Brnsted-Lowry Theory In a Brnsted-Lowry acidbase reaction, an H
+ is transferred The acid is an H donor The base is an H acceptor
base structure must contain an atom with an unshared pair of
electrons In a Brnsted-Lowry acid-base reaction, the acid molecule
gives an H + to the base molecule HA + :B :A + HB + Tro, Chemistry:
A Molecular Approach, 2/e
Slide 19
Brnsted-Lowry Acids Brnsted-Lowry acids are H + donors any
material that has H can potentially be a Brnsted-Lowry acid because
of the molecular structure, often one H in the molecule is easier
to transfer than others When HCl dissolves in water, the HCl is the
acid because HCl transfers an H + to H 2 O, forming H 3 O + ions
water acts as base, accepting H + HCl(aq) + H 2 O(l) Cl (aq) + H 3
O + (aq) acidbase Tro, Chemistry: A Molecular Approach, 2/e
Slide 20
Brnsted-Lowry Bases Brnsted-Lowry bases are H + acceptors any
material that has atoms with lone pairs can potentially be a
Brnsted-Lowry base because of the molecular structure, often one
atom in the molecule is more willing to accept H + transfer than
others When NH 3 dissolves in water, the NH 3 (aq) is the base
because NH 3 accepts an H + from H 2 O, forming OH (aq) water acts
as acid, donating H + NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH (aq)
base acid Tro, Chemistry: A Molecular Approach, 2/e
Slide 21
A Warning! Because chemists know common bonding patterns, we
often do not draw lone pair electrons on our structures. You need
to be able to recognize when an atom in a molecule has lone pair
electrons and when it doesnt! Tro, Chemistry: A Molecular Approach,
2/e
Slide 22
Practice Draw structures of the following that include lone
pairs of electrons HClO HCO 3 Tro, Chemistry: A Molecular Approach,
2/e
Slide 23
Amphoteric Substances Amphoteric substances can act as either
an acid or a base because they have both a transferable H and an
atom with lone pair electrons Water acts as base, accepting H +
from HCl HCl(aq) + H 2 O(l) Cl (aq) + H 3 O + (aq) Water acts as
acid, donating H + to NH 3 NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH
(aq) Tro, Chemistry: A Molecular Approach, 2/e
Slide 24
Brnsted-Lowry Acid-Base Reactions One of the advantages of
Brnsted-Lowry theory is that it allows reactions to be reversible
HA + :B :A + HB + The original base has an extra H + after the
reaction, so it will act as an acid in the reverse process And the
original acid has a lone pair of electrons after the reaction so it
will act as a base in the reverse process :A + HB + HA + :B Tro,
Chemistry: A Molecular Approach, 2/e
Slide 25
Conjugate Pairs In a Brnsted-Lowry acidbase reaction, the
original base becomes an acid in the reverse reaction, and the
original acid becomes a base in the reverse process Each reactant
and the product it becomes is called a conjugate pair The original
base becomes its conjugate acid; and the original acid becomes its
conjugate base Tro, Chemistry: A Molecular Approach, 2/e
Slide 26
Brnsted-Lowry AcidBase Reactions HA + :B :A +HB +
acidbaseconjugate conjugate base acid HCHO 2 + H 2 O CHO 2 +H 3 O +
acid baseconjugate conjugate base acid H 2 O + NH 3 HO +NH 4 + acid
baseconjugate conjugate base acid Tro, Chemistry: A Molecular
Approach, 2/e
Slide 27
Conjugate Pairs In the reaction H 2 O + NH 3 HO + NH 4 + H 2 O
and HO constitute an acid/conjugate base pair NH 3 and NH 4 +
constitute a base/conjugate acid pair Tro, Chemistry: A Molecular
Approach, 2/e
Slide 28
Practice Write the formula for the conjugate acid of the
following H 2 O NH 3 CO 3 2 H 2 PO 4 1 H 2 OH 3 O + NH 3 NH 4 + CO
3 2 HCO 3 H 2 PO 4 1 H 3 PO 4 Tro, Chemistry: A Molecular Approach,
2/e
Slide 29
Practice Write the formula for the conjugate base of the
following H 2 O NH 3 CO 3 2 H 2 PO 4 1 H 2 OHO NH 3 NH 2 CO 3 2
because CO 3 2 does not have an H, it cannot be an acid H 2 PO 4 1
HPO 4 2 Tro, Chemistry: A Molecular Approach, 2/e
Slide 30
Practice Identify the Brnsted-Lowry acid, base, conjugate acid,
and conjugate base in the following reaction HSO 4 (aq) + HCO 3
(aq) SO 4 2 (aq) + H 2 CO 3(aq) Base Conjugate Acid Conjugate Base
Tro, Chemistry: A Molecular Approach, 2/e
Slide 31
PracticeWrite the equations for the following reacting with
water and acting as a monoprotic acid & label the conjugate
acid and base HBr + H 2 O Br + H 3 O + Acid Base Conj. Conj. base
acid HSO 4 + H 2 O SO 4 2 + H 3 O + Acid Base Conj. Conj. base acid
HBr HSO 4 Tro, Chemistry: A Molecular Approach, 2/e
Slide 32
PracticeWrite the equations for the following reacting with
water and acting as a monoprotic-accepting base and label the
conjugate acid and base I + H 2 O HI + OH Base Acid Conj. Conj.
acid base I CO 3 2 CO 3 2 + H 2 O HCO 3 + OH Base Acid Conj. Conj.
acid base Tro, Chemistry: A Molecular Approach, 2/e
Slide 33
Comparing Arrhenius Theory and Brnsted-Lowry Theory Brnsted
Lowry theory HCl(aq) + H 2 O(l) Cl (aq) + H 3 O + (aq) HF(aq) + H 2
O(l) F (aq) + H 3 O + (aq) NaOH(aq) Na + (aq) + OH (aq) NH 3 (aq) +
H 2 O(l) NH 4 + (aq) + OH (aq) Arrhenius theory HCl(aq) H + (aq) +
Cl (aq) HF(aq) H + (aq) + F (aq) NaOH(aq) Na + (aq) + OH (aq) NH 4
OH(aq) NH 4 + (aq) + OH (aq) Tro, Chemistry: A Molecular Approach,
2/e
Slide 34
Strong or Weak A strong acid is a strong electrolyte
practically all the acid molecules ionize, A strong base is a
strong electrolyte practically all the base molecules form OH ions,
either through dissociation or reaction with water, A weak acid is
a weak electrolyte only a small percentage of the molecules ionize,
A weak base is a weak electrolyte only a small percentage of the
base molecules form OH ions, either through dissociation or
reaction with water, Tro, Chemistry: A Molecular Approach, 2/e
Slide 35
Strong Acids HCl H + + Cl HCl + H 2 O H 3 O + + Cl 0.10 M HCl =
0.10 M H 3 O + The stronger the acid, the more willing it is to
donate H we use water as the standard base to donate H to Strong
acids donate practically all their Hs 100% ionized in water strong
electrolyte [H 3 O + ] = [strong acid] [X] means the molarity of X
Tro, Chemistry: A Molecular Approach, 2/e
Slide 36
HF H + + F HF + H 2 O H 3 O + + F 0.10 M HF 0.10 M H 3 O + Weak
Acids Weak acids donate a small fraction of their Hs most of the
weak acid molecules do not donate H to water much less than 1%
ionized in water [H 3 O + ]
General Trends in Acidity The stronger an acid is at donating
H, the weaker the conjugate base is at accepting H Higher oxidation
number = stronger oxyacid H 2 SO 4 > H 2 SO 3 ; HNO 3 > HNO 2
Cation stronger acid than neutral molecule; neutral stronger acid
than anion H 3 O + > H 2 O > OH ; NH 4 + > NH 3 > NH 2
trend in base strength opposite Tro, Chemistry: A Molecular
Approach, 2/e
Slide 41
Acid Ionization Constant, K a Acid strength measured by the
size of the equilibrium constant when reacts with H 2 O HAcid + H 2
O Acid + H 3 O + The equilibrium constant for this reaction is
called the acid ionization constant, K a larger K a = stronger acid
Tro, Chemistry: A Molecular Approach, 2/e
Slide 42
Slide 43
Autoionization of Water Water is actually an extremely weak
electrolyte therefore there must be a few ions present About 2 out
of every 1 billion water molecules form ions through a process
called autoionization H 2 O H + + OH H 2 O + H 2 O H 3 O + + OH All
aqueous solutions contain both H 3 O + and OH the concentration of
H 3 O + and OH are equal in water [H 3 O + ] = [OH ] = 10 7 M @ 25
C Tro, Chemistry: A Molecular Approach, 2/e
Slide 44
Ion Product of Water The product of the H 3 O + and OH
concentrations is always the same number The number is called the
Ion Product of Water and has the symbol K w aka the Dissociation
Constant of Water [H 3 O + ] x [OH ] = K w = 1.00 x 10 14 @ 25 C if
you measure one of the concentrations, you can calculate the other
As [H 3 O + ] increases the [OH ] must decrease so the product
stays constant inversely proportional Tro, Chemistry: A Molecular
Approach, 2/e
Slide 45
Acidic and Basic Solutions All aqueous solutions contain both H
3 O + and OH ions Neutral solutions have equal [H 3 O + ] and [OH ]
[H 3 O + ] = [OH ] = 1.00 x 10 7 Acidic solutions have a larger [H
3 O + ] than [OH ] [H 3 O + ] > 1.00 x 10 7 ; [OH ] < 1.00 x
10 7 Basic solutions have a larger [OH ] than [H 3 O + ] [H 3 O + ]
1.00 x 10 7 Tro, Chemistry: A Molecular Approach, 2/e
Practice Complete the table [H + ] vs. [OH ] OH H+H+ H+H+ H+H+
H+H+ H+H+ [OH ]10 14 10 13 10 11 10 9 10 7 10 5 10 3 10 1 10 0 [H +
] 10 0 10 1 10 3 10 5 10 7 10 9 10 11 10 13 10 14 Even though it
may look like it, neither H + nor OH will ever be 0 The sizes of
the H + and OH are not to scale because the divisions are powers of
10 rather than units Acid Base Tro, Chemistry: A Molecular
Approach, 2/e
Slide 48
Practice Determine the [H 3 O + ] when the [OH ] = 2.5 x 10 9 M
the units are correct; the fact that the [H 3 O + ] > [OH ]
means the solution is acidic [OH ] = 2.5 x 10 9 M [H 3 O + ] Check:
Solution: Conceptual Plan: Relationships: Given: Find: [OH ][H 3 O
+ ] Tro, Chemistry: A Molecular Approach, 2/e
Slide 49
Measuring Acidity: pH The acidity or basicity of a solution is
often expressed as pH pH = log[H 3 O + ] exponent on 10 with a
positive sign pH water = log[10 7 ] = 7 need to know the [H 3 O + ]
concentration to find pH pH 7 is basic, pH = 7 is neutral [H 3 O +
] = 10 pH Tro, Chemistry: A Molecular Approach, 2/e
Slide 50
Sig. Figs. & Logs When you take the log of a number written
in scientific notation, the digit(s) before the decimal point come
from the exponent on 10, and the digits after the decimal point
come from the decimal part of the number log(2.0 x 10 6 ) = log(10
6 ) + log(2.0) = 6 + 0.30303 = 6.30303... Because the part of the
scientific notation number that determines the significant figures
is the decimal part, the sig figs are the digits after the decimal
point in the log log(2.0 x 10 6 ) = 6.30 Tro, Chemistry: A
Molecular Approach, 2/e
Slide 51
What Does the pH Number Imply? The lower the pH, the more
acidic the solution; the higher the pH, the more basic the solution
1 pH unit corresponds to a factor of 10 difference in acidity
Normal range of pH is 0 to 14 pH 0 is [H 3 O + ] = 1 M, pH 14 is
[OH ] = 1 M pH can be negative (very acidic) or larger than 14
(very alkaline) Tro, Chemistry: A Molecular Approach, 2/e
Slide 52
Practice Determine the pH @ 25 C of a solution that has [OH ] =
2.5 x 10 9 M pH is unitless; the fact that the pH < 7 means the
solution is acidic [OH ] = 2.5 x 10 9 M pH Check: Solution:
Conceptual Plan: Relationships: Given: Find: [H 3 O + ][OH ]pH Tro,
Chemistry: A Molecular Approach, 2/e
Slide 53
Practice Determine the [OH ] of a solution with a pH of 5.40
because the pH < 7, [OH ] should be less than 1 x 10 7 ; and it
is pH = 5.40 [OH ], M Check: Solution: Conceptual Plan:
Relationships: Given: Find: [H 3 O + ]pH[OH ] Tro, Chemistry: A
Molecular Approach, 2/e
Slide 54
pOH Another way of expressing the acidity/basicity of a
solution is pOH pOH = log[OH ], [OH ] = 10 pOH pOH water = log[10 7
] = 7 need to know the [OH ] concentration to find pOH pOH 7 is
acidic, pOH = 7 is neutral pH + pOH = 14.0 Tro, Chemistry: A
Molecular Approach, 2/e
Relationship between pH and pOH pH + pOH = 14.00 at 25 C you
can use pOH to find pH of a solution Tro, Chemistry: A Molecular
Approach, 2/e
Slide 58
Practice Determine the pOH @ 25 C of a solution that has [H 3 O
+ ] = 2.5 x 10 9 M pH is unitless; the fact that the pH < 7
means the solution is acidic [H 3 O + ] = 2.5 x 10 9 M pOH Check:
Solution: Conceptual Plan: Relationships: Given: Find: pH[H 3 O +
]pOH Tro, Chemistry: A Molecular Approach, 2/e
Slide 59
pKpK A way of expressing the strength of an acid or base is pK
pK a = log(K a ), K a = 10 pKa pK b = log(K b ), K b = 10 pKb The
stronger the acid, the smaller the pK a larger K a = smaller pK a
because it is the log The stronger the base, the smaller the pK b
larger K b = smaller pK b Tro, Chemistry: A Molecular Approach,
2/e
Slide 60
[H 3 O + ] and [OH ] in a Strong Acid or Strong Base Solution
There are two sources of H 3 O + in an aqueous solution of a strong
acid the acid and the water There are two sources of OH in an
aqueous solution of a strong acid the base and the water For a
strong acid or base, the contribution of the water to the total [H
3 O + ] or [OH ] is negligible the [H 3 O + ] acid shifts the K w
equilibrium so far that [H 3 O + ] water is too small to be
significant except in very dilute solutions, generally < 1 x 10
4 M Tro, Chemistry: A Molecular Approach, 2/e
Slide 61
Finding pH of a Strong Acid or Strong Base Solution For a
monoprotic strong acid [H 3 O + ] = [HAcid] for polyprotic acids,
the other ionizations can generally be ignored for H 2 SO 4, the
second ionization cannot be ignored 0.10 M HCl has [H 3 O + ] =
0.10 M and pH = 1.00 For a strong ionic base, [OH ] = (number OH
)x[Base] for molecular bases with multiple lone pairs available,
only one lone pair accepts an H, the other reactions can generally
be ignored 0.10 M Ca(OH) 2 has [OH ] = 0.20 M and pH = 13.30 Tro,
Chemistry: A Molecular Approach, 2/e
Slide 62
Finding the pH of a Weak Acid There are also two sources of H 3
O + in an aqueous solution of a weak acid the acid and the water
However, finding the [H 3 O + ] is complicated by the fact that the
acid only undergoes partial ionization Calculating the [H 3 O + ]
requires solving an equilibrium problem for the reaction that
defines the acidity of the acid HAcid + H 2 O Acid + H 3 O + Tro,
Chemistry: A Molecular Approach, 2/e
Slide 63
Practice What is the pH of a 0.012 M solution of nicotinic
acid, HC 6 H 4 NO 2 ? write the reaction for the acid with water
construct an ICE table for the reaction enter the initial
concentrations assuming the [H 3 O + ] from water is 0 HC 6 H 4 NO
2 + H 2 O C 6 H 4 NO 2 + H 3 O + [HA][A ][H 3 O + ] initial 0.012 0
0 change equilibrium Tro, Chemistry: A Molecular Approach, 2/e
Slide 64
[HA][A ][H 3 O + ] initial 0.012 00 change equilibrium Practice
What is the pH of a 0.012 M solution of nicotinic acid, HC 6 H 4 NO
2 ? represent the change in the concentrations in terms of x sum
the columns to find the equilibrium concentrations in terms of x
substitute into the equilibrium constant expression +x+x +x+x xx
0.012 x xx HC 6 H 4 NO 2 + H 2 O C 6 H 4 NO 2 + H 3 O + Tro,
Chemistry: A Molecular Approach, 2/e
Slide 65
Practice What is the pH of a 0.012 M solution of nicotinic
acid, HC 6 H 4 NO 2 ? K a = 1.4 x 10 5 @ 25 C determine the value
of K a because K a is very small, approximate the [HA] eq = [HA]
init and solve for x [HA][A ][H 3 O + ] initial 0.012 0 0 change
xx+x+x+x+x equilibrium 0.012xx 0.012 x HC 6 H 4 NO 2 + H 2 O C 6 H
4 NO 2 + H 3 O + Tro, Chemistry: A Molecular Approach, 2/e
Slide 66
Practice What is the pH of a 0.012 M solution of nicotinic
acid, HC 6 H 4 NO 2 ? K a = 1.4 x 10 5 @ 25 C check if the
approximation is valid by seeing if x < 5% of [HC 6 H 4 NO 2 ]
init K a for HC 6 H 4 NO 2 = 1.4 x 10 5 the approximation is valid
x = 4.1 x 10 4 [HA][A ][H 3 O + ] initial 0.012 0 0 change
xx+x+x+x+x equilibrium 0.012 xx Tro, Chemistry: A Molecular
Approach, 2/e
Slide 67
Practice What is the pH of a 0.012 M solution of nicotinic
acid, HC 6 H 4 NO 2 ? K a = 1.4 x 10 5 @ 25 C substitute x into the
equilibrium concentration definitions and solve x = 4.1 x 10 4
[HA][A ][H 3 O + ] initial 0.012 0 0 change xx+x+x+x+x equilibrium
0.012x xx Tro, Chemistry: A Molecular Approach, 2/e
Slide 68
Practice What is the pH of a 0.012 M solution of nicotinic
acid, HC 6 H 4 NO 2 ? K a = 1.4 x 10 5 @ 25 C substitute [H 3 O + ]
into the formula for pH and solve [HA][A ][H 3 O + ] initial 0.012
0 0 change xx+x+x+x+x equilibrium 0.0120.00041 Tro, Chemistry: A
Molecular Approach, 2/e
Slide 69
Practice What is the pH of a 0.012 M solution of nicotinic
acid, HC 6 H 4 NO 2 ? K a = 1.4 x 10 5 @ 25 C check by substituting
the equilibrium concentrations back into the equilibrium constant
expression and comparing the calculated K a to the given K a the
values match [HA][A ][H 3 O + ] initial 0.012 0 0 change xx+x+x+x+x
equilibrium 0.0120.00041 Tro, Chemistry: A Molecular Approach,
2/e
Slide 70
Practice What is the K a of nicotinic acid, HC 6 H 4 NO 2, if a
0.012 M solution of nicotinic acid has a pH of 3.40? use the pH to
find the equilibrium [H 3 O + ] write the reaction for the acid
with water construct an ICE table for the reaction enter the
initial concentrations and [H 3 O + ] equil HA + H 2 O A + H 3 O +
[HA][A ][H 3 O + ] initial change equilibrium [HA][A ][H 3 O + ]
initial 0.012 0 0 change equilibrium 4.0E-04 Tro, Chemistry: A
Molecular Approach, 2/e
Slide 71
[HA][A ][H 3 O + ] initial 0.012 00 change equilibrium 0.012
Practice What is the K a of nicotinic acid, HC 6 H 4 NO 2, if a
0.012 M solution of nicotinic acid has a pH of 3.40? fill in the
rest of the table using the [H 3 O + ] as a guide if the difference
is insignificant, [HA] equil = [HA] initial substitute into the K a
expression and compute K a +4.0E-04 4.0E-04 0.012 4.0E-04 HA + H 2
O A + H 3 O + Tro, Chemistry: A Molecular Approach, 2/e
Slide 72
Polyprotic Acids Acid molecules often have more than one
ionizable H these are called polyprotic acids the ionizable Hs may
have different acid strengths or be equal 1 H = monoprotic, 2 H =
diprotic, 3 H = triprotic HCl = monoprotic, H 2 SO 4 = diprotic, H
3 PO 4 = triprotic Polyprotic acids ionize in steps each ionizable
H is removed sequentially Removing of the first H automatically
makes removal of the second H harder H 2 SO 4 is a stronger acid
than HSO 4 Tro, Chemistry: A Molecular Approach, 2/e
Slide 73
Percent Ionization Another way to measure the strength of an
acid is to determine the percentage of acid molecules that ionize
when dissolved in water this is called the percent ionization the
higher the percent ionization, the stronger the acid Because
[ionized acid] equil = [H 3 O + ] equil Tro, Chemistry: A Molecular
Approach, 2/e
Slide 74
Practice What is the percent ionization of a 0.012 M solution
of nicotinic acid, HC 6 H 4 NO 2 ? write the reaction for the acid
with water construct an ICE table for the reaction enter the
initial concentrations assuming the [H 3 O + ] from water is 0 HC 6
H 4 NO 2 + H 2 O C 6 H 4 NO 2 + H 3 O + [HA][A ][H 3 O + ] initial
0.012 0 0 change equilibrium Tro, Chemistry: A Molecular Approach,
2/e
Slide 75
[HA][A ][H 3 O + ] initial 0.012 00 change equilibrium Practice
What is the percent ionization of a 0.012 M solution of nicotinic
acid, HC 6 H 4 NO 2 ? represent the change in the concentrations in
terms of x sum the columns to find the equilibrium concentrations
in terms of x substitute into the equilibrium constant expression
+x+x +x+x xx 0.012 x xx HC 6 H 4 NO 2 + H 2 O C 6 H 4 NO 2 + H 3 O
+ Tro, Chemistry: A Molecular Approach, 2/e
Slide 76
Practice What is the percent ionization of a 0.012 M solution
of nicotinic acid, HC 6 H 4 NO 2 ? K a = 1.4 x 10 5 determine the
value of K a because K a is very small, approximate the [HA] eq =
[HA] init and solve for x [HA][A ][H 3 O + ] initial 0.012 0 0
change xx+x+x+x+x equilibrium 0.012xx 0.012 x HC 6 H 4 NO 2 + H 2 O
C 6 H 4 NO 2 + H 3 O + Tro, Chemistry: A Molecular Approach,
2/e
Slide 77
Practice What is the percent ionization of a 0.012 M solution
of nicotinic acid, HC 6 H 4 NO 2 ? substitute x into the
equilibrium concentration definitions and solve x = 4.1 x 10 4
[HA][A ][H 3 O + ] initial 0.012 0 0 change xx+x+x+x+x equilibrium
0.012x xx Tro, Chemistry: A Molecular Approach, 2/e
Slide 78
Practice What is the percent ionization of a 0.012 M solution
of nicotinic acid, HC 6 H 4 NO 2 ? apply the definition and compute
the percent ionization because the percent ionization is < 5%,
the x is small approximation is valid [HA][A ][H 3 O + ] initial
0.012 0 0 change xx+x+x+x+x equilibrium 0.0124.1E-04 Tro,
Chemistry: A Molecular Approach, 2/e
Slide 79
Relationship Between [H 3 O + ] equilibrium & [HA] initial
Increasing the initial concentration of acid results in increased
[H 3 O + ] at equilibrium Increasing the initial concentration of
acid results in decreased percent ionization This means that the
increase in [H 3 O + ] concentration is slower than the increase in
acid concentration Tro, Chemistry: A Molecular Approach, 2/e
Slide 80
Why doesnt the increase in H 3 O + keep up with the increase in
HA? The reaction for ionization of a weak acid is HA (aq) + H 2 O
(l) A (aq) + H 3 O + (aq) According to Le Chteliers Principle, if
we reduce the concentrations of all the (aq) components, the
equilibrium should shift to the right to increase the total number
of dissolved particles we can reduce the (aq) concentrations by
using a more dilute initial acid concentration The result will be a
larger [H 3 O + ] in the dilute solution compared to the initial
acid concentration This will result in a larger percent ionization
Tro, Chemistry: A Molecular Approach, 2/e
Slide 81
Finding the pH of Mixtures of Acids Generally, you can ignore
the contribution of the weaker acid to the [H 3 O + ] equil For a
mixture of a strong acid with a weak acid, the complete ionization
of the strong acid provides more than enough [H 3 O + ] to shift
the weak acid equilibrium to the left so far that the weak acids
added [H 3 O + ] is negligible For mixtures of weak acids,
generally only need to consider the stronger for the same reasons
as long as one is significantly stronger than the other, and their
concentrations are similar Tro, Chemistry: A Molecular Approach,
2/e
Slide 82
Practice Determine the pH @ 25 C of a solution that is a
mixture of 0.045 M HCl and 0.15 M HF pH is unitless; the fact that
the pH < 7 means the solution is acidic [HCl] = 4.5 x 10 2 M,
[HF] = 0.15 M pH Check: Solution: Conceptual Plan: Relationships:
Given: Find: [H 3 O + ][HCl]pH Because HCl is a strong acid and HF
is a weak acid, [H 3 O + ] = [HCl] Tro, Chemistry: A Molecular
Approach, 2/e
Slide 83
Strong Bases NaOH Na + + OH The stronger the base, the more
willing it is to accept H use water as the standard acid For ionic
bases, practically all units are dissociated into OH or accept Hs
strong electrolyte multi-OH strong bases completely dissociated [HO
] = [strong base] x (# OH) Tro, Chemistry: A Molecular Approach,
2/e
Slide 84
Practice Calculate the pH of the following strong acid or base
solutions 0.0020 M HCl 0.0015 M Ca(OH) 2 [H 3 O + ] = [HCl] = 2.0 x
10 3 M pH = log(2.0 x 10 3 ) = 2.70 [OH ] = 2 x [Ca(OH) 2 ] = 3.0 x
10 3 M pOH = log(3.0 x 10 3 ) = 2.52 pH = 14.00 pOH = 14.00 2.52 pH
= 11.48
Slide 85
Weak Bases NH 3 + H 2 O NH 4 + + OH In weak bases, only a small
fraction of molecules accept Hs weak electrolyte most of the weak
base molecules do not take H from water much less than 1%
ionization in water [HO ]
Ionization in Polyprotic Acids Because polyprotic acids ionize
in steps, each H has a separate K a K a1 > K a2 > K a3
Generally, the difference in K a values is great enough so that the
second ionization does not happen to a large enough extent to
affect the pH most pH problems just do first ionization except H 2
SO 4 use [H 2 SO 4 ] as the [H 3 O + ] for the second ionization [A
2 ] = K a2 as long as the second ionization is negligible Tro,
Chemistry: A Molecular Approach, 2/e
Slide 113
Slide 114
Practice What is the pH of a 0.12 M solution of carbonic acid,
H 2 CO 3 ? write the reactions for the acid with water one H at a
time construct an ICE table for the reaction enter the initial
concentrations assuming the second ionization is negligible H 2 CO
3 + H 2 O HCO 3 + H 3 O + [HA][A ][H 3 O + ] initial 0.12 0 0
change equilibrium HCO 3 + H 2 O CO 3 2 + H 3 O + Tro, Chemistry: A
Molecular Approach, 2/e
Slide 115
[HA][A ][H 3 O + ] initial 0.12 00 change equilibrium Practice
What is the pH of a 0.12 M solution of carbonic acid, H 2 CO 3 ?
represent the change in the concentrations in terms of x sum the
columns to find the equilibrium concentrations in terms of x
substitute into the equilibrium constant expression +x+x +x+x xx
0.12 x xx H 2 CO 3 + H 2 O HCO 3 + H 3 O + Tro, Chemistry: A
Molecular Approach, 2/e
Slide 116
Practice What is the pH of a 0.12 M solution of carbonic acid,
H 2 CO 3 ? determine the value of K a1 because K a1 is very small,
approximate the [HA] eq = [HA] init and solve for x [HA][A ][H 3 O
+ ] initial 0.12 0 0 change xx+x+x+x+x equilibrium 0.012xx 0.12 x K
a1 = 4.3 x 10 7, K a2 = 5.6 x 10 11 Tro, Chemistry: A Molecular
Approach, 2/e
Slide 117
Practice What is the pH of a 0.12 M solution of carbonic acid,
H 2 CO 3 ? check if the approximation is valid by seeing if x <
5% of [H 2 CO 3 ] init K a1 for H 2 CO 3 = 4.3 x 10 7 the
approximation is valid x = 2.27 x 10 4 [HA][A ][H 3 O + ] initial
0.12 0 0 change xx+x+x+x+x equilibrium 0.12 xx Tro, Chemistry: A
Molecular Approach, 2/e
Slide 118
Practice What is the pH of a 0.12 M solution of carbonic acid,
H 2 CO 3 ? substitute x into the equilibrium concentration
definitions and solve x = 2.3 x 10 4 [HA][A ][H 3 O + ] initial
0.12 0 0 change xx+x+x+x+x equilibrium 0.12x xx Tro, Chemistry: A
Molecular Approach, 2/e
Slide 119
Practice What is the pH of a 0.12 M solution of carbonic acid,
H 2 CO 3 ? substitute [H 3 O + ] into the formula for pH and solve
[HA][A ][H 3 O + ] initial 0.12 0 0 change xx+x+x+x+x equilibrium
0.120.00023 Tro, Chemistry: A Molecular Approach, 2/e
Slide 120
Practice What is the pH of a 0.12 M solution of carbonic acid,
H 2 CO 3 ? check by substituting the equilibrium concentrations
back into the equilibrium constant expression and comparing the
calculated K a to the given K a the values match within sig figs
[HA][A ][H 3 O + ] initial 0.12 0 0 change xx+x+x+x+x equilibrium
0.120.00023 K a1 for H 2 CO 3 = 4.3 x 10 7 Tro, Chemistry: A
Molecular Approach, 2/e
Slide 121
Practice What is the [CO 3 2 ] in a 0.12 M solution of carbonic
acid, H 2 CO 3 ? write the reactions for the acid with water one H
at a time construct an ICE table for the reaction enter the initial
concentrations for the second ionization using the equilibrium
concentrations from first ionization H 2 CO 3 + H 2 O HCO 3 + H 3 O
+ [HCO 3 ][CO 3 2 ][H 3 O + ] initial 0.00023 0 change equilibrium
HCO 3 + H 2 O CO 3 2 + H 3 O + Tro, Chemistry: A Molecular
Approach, 2/e
Slide 122
[HCO 3 ][CO 3 2 ][H 3 O + ] initial 0.00023 0 change
equilibrium Practice What is the [CO 3 2 ] in a 0.12 M solution of
carbonic acid, H 2 CO 3 ? represent the change in the
concentrations in terms of x sum the columns to find the
equilibrium concentrations in terms of x substitute into the
equilibrium constant expression +x+x +x+x xx 2.3E4 x x HCO 3 + H 2
O CO 3 2 + H 3 O + 2.3E4 +x Tro, Chemistry: A Molecular Approach,
2/e
Slide 123
Practice What is the [CO 3 2 ] in a 0.12 M solution of carbonic
acid, H 2 CO 3 ? determine the value of K a2 because K a2 is very
small, approximate the [HA] eq = [HA] init, [H 3 O + ] eq = [H 3 O
+ ] init, and solve for x using this approximation, it is seen that
x = K a2. Therefore [CO 3 2 ] = K a2 K a1 = 4.3 x 10 7, K a2 = 5.6
x 10 11 [HCO 3 ][CO 3 2 ][H 3 O + ] initial 0.00023 0 change
xx+x+x+x+x equilibrium 2.3E4 x x 2.3E4 + x [HCO 3 ][CO 3 2 ][H 3 O
+ ] initial 0.00023 0 change xx+x+x+x+x equilibrium 2.3E4x Tro,
Chemistry: A Molecular Approach, 2/e
Slide 124
Ionization in H 2 SO 4 The ionization constants for H 2 SO 4
are H 2 SO 4 + H 2 O HSO 4 + H 3 O + strong HSO 4 + H 2 O SO 4 2 +
H 3 O + K a2 = 1.2 x 10 2 For most sulfuric acid solutions, the
second ionization is significant and must be accounted for Because
the first ionization is complete, use the given [H 2 SO 4 ] = [HSO
4 ] initial = [H 3 O + ] initial Tro, Chemistry: A Molecular
Approach, 2/e
Slide 125
Example 15.18: Find the pH of 0.0100 M H 2 SO 4 (aq) solution @
25 C write the reactions for the acid with water construct an ICE
table for the second ionization reaction enter the initial
concentrations assuming the [HSO 4 ] and [H 3 O + ] is [H 2 SO 4 ]
[HSO 4 ][SO 4 2 ][H 3 O + ] initial 0.01000 change equilibrium HSO
4 + H 2 O SO 4 2 + H 3 O + H 2 SO 4 + H 2 O HSO 4 + H 3 O + Tro,
Chemistry: A Molecular Approach, 2/e
Slide 126
Example 15.18: Find the pH of 0.0100 M H 2 SO 4 (aq) solution @
25 C represent the change in the concentrations in terms of x sum
the columns to find the equilibrium concentrations in terms of x
substitute into the equilibrium constant expression [HSO 4 ][SO 4 2
][H 3 O + ] initial 0.01000 change xx+x+x+x+x equilibrium 0.0100 x
x Tro, Chemistry: A Molecular Approach, 2/e126
Slide 127
Example 15.18: Find the pH of 0.0100 M H 2 SO 4 (aq) solution @
25 C expand and solve for x using the quadratic formula K a for HSO
4 = 0.012 Tro, Chemistry: A Molecular Approach, 2/e127
Slide 128
Example 15.18: Find the pH of 0.0100 M H 2 SO 4 (aq) solution @
25 C substitute x into the equilibrium concentration definitions
and solve x = 0.0045 [HSO 4 ][SO 4 2 ][H 3 O + ] initial 0.01000
change xx+x+x+x+x equilibrium 0.0100 xx K a for HSO 4 = 0.012 [HSO
4 ][SO 4 2 ][H 3 O + ] initial 0.01000 change xx+x+x+x+x
equilibrium 0.00550.00450.0145 Tro, Chemistry: A Molecular
Approach, 2/e128
Slide 129
Example 15.18: Find the pH of 0.0100 M H 2 SO 4 (aq) solution @
25 C substitute [H 3 O + ] into the formula for pH and solve K a
for HSO 4 = 0.012 [HSO 4 ][SO 4 2 ][H 3 O + ] initial 0.01000
change xx+x+x+x+x equilibrium 0.00550.00450.0145 Tro, Chemistry: A
Molecular Approach, 2/e129
Slide 130
Example 15.18: Find the pH of 0.0100 M H 2 SO 4 (aq) solution @
25 C check by substituting the equilibrium concentrations back into
the equilibrium constant expression and comparing the calculated K
a to the given K a the answer matches K a for HSO 4 = 0.012 [HSO 4
][SO 4 2 ][H 3 O + ] initial 0.01000 change xx+x+x+x+x equilibrium
0.00550.00450.0145 Tro, Chemistry: A Molecular Approach, 2/e
Slide 131
Strengths of Binary Acids The more + HX polarized the bond, the
more acidic the bond The stronger the HX bond, the weaker the acid
Binary acid strength increases to the right across a period
acidity: HC < HN < HO < HF Binary acid strength increases
down the column acidity: HF < HCl < HBr < HI Tro,
Chemistry: A Molecular Approach, 2/e
Slide 132
Relationship between Bond Strength and Acidity Acid Bond Energy
kJ/mol Type of Acid HF565weak HCl431strong HBr364strong Tro,
Chemistry: A Molecular Approach, 2/e
Slide 133
Strengths of Oxyacids, HOY The more electronegative the Y atom,
the stronger the oxyacid HClO > HIO acidity of oxyacids
decreases down a group same trend as binary acids helps weakens the
HO bond The larger the oxidation number of the central atom, the
stronger the oxyacid H 2 CO 3 > H 3 BO 3 acidity of oxyacids
increases to the right across a period opposite trend of binary
acids The more oxygens attached to Y, the stronger the oxyacid
further weakens and polarizes the HO bond HClO 3 > HClO 2 Tro,
Chemistry: A Molecular Approach, 2/e
Slide 134
Relationship Between Electronegativity and Acidity Acid HOY
Electronegativity of Y KaKa HOCl3.02.9 x 10 8 HOBr2.82.0 x 10 9
HOIHOI2.52.3 x 10 11 Tro, Chemistry: A Molecular Approach, 2/e
Slide 135
Relationship Between Number of Oxygens on the Central Atom and
Acidity Tro, Chemistry: A Molecular Approach, 2/e
Slide 136
Practice Order the Following By Acidity (Least to Most) H 3 PO
4 HNO 3 H 3 PO 3 H 3 AsO 3 By Acidity (Least to Most) HClHBrH 2 SHS
By Basicity (Least to Most) CO 3 2 NO 3 HCO 3 BO 3 3 Tro,
Chemistry: A Molecular Approach, 2/e136
Slide 137
Practice Order the Following By Acidity (Least to Most) H 3 PO
4 HNO 3 H 3 PO 3 H 3 AsO 3 H 3 AsO 3 < H 3 PO 3 < H 3 PO 4
< HNO 3 By Acidity (Least to Most) HClHBrH 2 SHS HS < H 2 S
< HCl < HBr By Basicity (Least to Most) CO 3 2 NO 3 HCO 3 BO
3 3 NO 3 < HCO 3 < CO 3 2 < BO 3 3 Tro, Chemistry: A
Molecular Approach, 2/e137
Slide 138
Lewis AcidBase Theory Lewis AcidBase theory focuses on
transferring an electron pair lone pair bond bond lone pair Does
NOT require H atoms The electron donor is called the Lewis Base
electron rich, therefore nucleophile The electron acceptor is
called the Lewis Acid electron deficient, therefore electrophile
Tro, Chemistry: A Molecular Approach, 2/e
Slide 139
Lewis Bases Lewis Base has electrons it is willing to give away
to or share with another atom Lewis Base must have lone pair of
electrons on it that it can donate Anions are better Lewis Bases
than neutral atoms or molecules N: < N: Generally, the more
electronegative an atom, the less willing it is to be a Lewis Base
O: < S: Tro, Chemistry: A Molecular Approach, 2/e
Slide 140
Lewis Acids Electron deficient, either from being attached to
electronegative atom(s) not having an octet Must have empty orbital
willing to accept the electron pair H + has empty 1s orbital B in
BF 3 has empty 2p orbital and an incomplete octet Many small,
highly charged metal cations have empty orbitals they can use to
accept electrons Atoms that are attached to highly electronegative
atoms and have multiple bonds can be Lewis Acids Tro, Chemistry: A
Molecular Approach, 2/e
Slide 141
Lewis AcidBase Reactions The base donates a pair of electrons
to the acid Generally results in a covalent bond forming H 3 N: +
BF 3 H 3 NBF 3 The product that forms is called an adduct Arrhenius
and Brnsted-Lowry acidbase reactions are also Lewis Tro, Chemistry:
A Molecular Approach, 2/e
Slide 142
Examples of Lewis AcidBase Reactions Tro, Chemistry: A
Molecular Approach, 2/e
Slide 143
Examples of Lewis AcidBase Reactions Ag + (aq) + 2 :NH 3(aq)
Ag(NH 3 ) 2 + (aq) Lewis Acid Lewis Base Adduct Tro, Chemistry: A
Molecular Approach, 2/e
Slide 144
Practice Identify the Lewis Acid and Lewis Base in Each
Reaction Lewis Base Lewis Base Lewis Acid Lewis Acid Tro,
Chemistry: A Molecular Approach, 2/e
Slide 145
U.S. Fuel Consumption Over 85% of the energy use in the United
States comes from the combustion of fossil fuels oil, natural gas,
coal Combustion of fossil fuels produces CO 2 CH 4 (g) + 2 O 2 (g)
CO 2 (g) + 2 H 2 O(g) Natural fossil fuels also contain small
amounts of S that burn to produce SO 2 (g) S(s) + O 2 (g) SO 2 (g)
The high temperatures of combustion allow N 2 (g) in the air to
combine with O 2 (g) to form oxides of nitrogen N 2 (g) + 2 O 2 (g)
2 NO 2 (g) Tro, Chemistry: A Molecular Approach, 2/e
Slide 146
What Is Acid Rain? Natural rain water has a pH of 5.6 naturally
slightly acidic due mainly to CO 2 Rain water with a pH lower than
5.6 is called acid rain Acid rain is linked to damage in ecosystems
and structures Tro, Chemistry: A Molecular Approach, 2/e
Slide 147
What Causes Acid Rain? Many natural and pollutant gases
dissolved in the air are nonmetal oxides CO 2, SO 2, NO 2 Nonmetal
oxides are acidic CO 2 (g) + H 2 O(l) H 2 CO 3 (aq) 2 SO 2 (g) + O
2 (g) + 2 H 2 O(l) 2 H 2 SO 4 (aq) 4 NO 2 (g) + O 2 (g) + 2 H 2
O(l) 4 HNO 3 (aq) Processes that produce nonmetal oxide gases as
waste increase the acidity of the rain natural volcanoes and some
bacterial action man-made combustion of fuel Tro, Chemistry: A
Molecular Approach, 2/e
Slide 148
pH of Rain in Different Regions Tro, Chemistry: A Molecular
Approach, 2/e148
Slide 149
Weather Patterns The prevailing winds in the United States
travel west to east Weather patterns may cause rain to be acidic in
regions other than where the nonmetal oxide is produced Much of the
northeast United States has rain of very low pH, even though it has
very low sulfur emissions, due in part to the general weather
patterns Tro, Chemistry: A Molecular Approach, 2/e
Slide 150
Sources of SO 2 from Utilities Tro, Chemistry: A Molecular
Approach, 2/e 150
Slide 151
Damage from Acid Rain Acids react with metals, and materials
that contain carbonates Acid rain damages bridges, cars, and other
metallic structures Acid rain damages buildings and other
structures made of limestone or cement Acidifying lakes affects
aquatic life Soil acidity causes more dissolving of minerals and
leaching more minerals from soil making it difficult for trees Tro,
Chemistry: A Molecular Approach, 2/e
Slide 152
Damage from Acid Rain Tro, Chemistry: A Molecular Approach,
2/e
Slide 153
Acid Rain Legislation 1990 Clean Air Act attacks acid rain
forces utilities to reduce SO 2 Result is acid rain in the
Northeast stabilized and beginning to be reduced Tro, Chemistry: A
Molecular Approach, 2/e