Sec 14'12: The Nature of Acids and Bases

1
Sec 14.1-2 The Nature of Acids and Bases

• 1. Acids classified as having a
  taste. Bases known for their
  taste.
• 2. Arrhenius Acid produce ions when
  dissolved in water. Bases produce
• Arrhenius only works for
  solutions.
• 3. Bronsted-Lowry Acid is a proton
  while a base is a proton
• Bronsted-Lowry works in phases
• Water can be an acid or a base, so it is
• When acting as a base water will accept a
  proton to produce
• HA (aq) H2O (l) ? H3O (aq) A- (aq)
• If H2O stronger base than A-
• If A- stronger base than H2O

sour
bitter
H
OH-
aqueous
donor
acceptor.
gaseous
amphoteric
H3O
?
?
2
Acid Strength and Dissociation Constant
Ka

• 1. The Ka expression is written without
  because it is a pure liquid.
• HA (aq) H2O (l) ? H3O (aq) A- (aq)
• Acid base
  Conjugate acid Conjugate base
• Or can be written as
• HA (aq) ? H (aq) A- (aq)
• Ka H3O A- H A-
• HA HA
• For a neutral aqueous solution (pH _____ H
  OH- 1.0.10-7M)
• Acidic solution HgtOH- Basic solution
  Hlt OH-
• H2O (l) H2O (l) ? H3O (aq) OH- (aq)
• 2. The larger the Ka, the
  the acid.
• Sample 14.1
• Al(H2O)63 (aq) ? H (aq) Al(H2O)5OH 2 (aq)
• Write the acid/base reactions for ammonia with
  water and ammonia with hydrochloric acid
• NH3 (aq) H2O (l) ? NH4 (aq) OH- (aq)
  
• HCl (aq) H2O (l) ? H3O (aq) Cl- (aq)

H2O
7.00
stronger
3

• Strong acids HCl HNO3 HClO4 H2SO4 (aq) (for
  1st ionization) (100 ionization)
• pg 658 for some strong acid pictures
• Sample 14.2 (strong vs. weak acids)
• The larger the Ka of the conjugate acid (or
  stronger the acid), the weaker the base
• Cl- will be the weakest base ( its conjugate
  acid (HCl) has the largest Ka)
• CN- will be the strongest base (its conjugate
  acid (HCN) has the smallest Ka)
• Sample 14.3
• Kw HOH-
• a. H Kw / OH-
• H 1.0.10-14 / 1.0.10-5
• H 1.0.10-9 M

Sample 14.4 By adding heat Kw
so heat is a making the
reaction Kw HOH- H2 H
(1.10-13)1/2 H OH- 3.10-7 M
endothermic
reactant
increases
H2O (l) ? H (aq) OH- (aq) 0
0 x x
4
Sec 14.3 pH Scale (pH meters are utilized to
measure pH of solutions)

• pH can show changes in H with
  small numbers (because the numbers
• are exponents). Significant digits (to the
  right of decimal)
• pH -log H pOH -log OH-
  pKa - log Ka
• pH pOH 14.00 Kw HOH- pKb -log Kb
• Sec 14.4 Calculating pH of Strong Acid Solutions
• Concentration of hydronium ion (or hydrogen ion)
  is _________ to the original concentration of the
  strong acid.
• Sample 14.5
• OH- 1.0.10-3 M
• pOH -log (1.0.10-3)
• pOH 3.00
• Sample 14.6
• pOH 14.00 pH 6.59
• pH -log H pOH -log OH-
• H 10-pH OH- 10-pOH
• H 10-7.41 OH- 10-6.59
• H 3.9.10-8 M OH- 2.6.10-7 M

large
equal
pH - log H pH -log (1.0.10-1) pH 1.00
5

• Sample 14.7 a.
• HNO3 (aq) ? H (aq) NO3- (aq)
• Initial 0.10 M 0
  0
• Final 0 0.10 M
  0.10 M
• Sample Exercise 14.7b.
• Looking at this you want to say the pH is
  but this is not true.
• Would adding acid to water make the solution go
  basic?
• Never
• Another equilibrium exists in any solution. The
  dissociation of
• Lets analyze this equilibrium
• HCl is a strong acid so in solution H from it
  is equal to 1.0.10 -10 M
• H2O (l) ? H (aq) OH-
  (aq)
• initial lots (not in K) 1.0.10-10 M
  0
• final still lots (not in K)
  1.0.10-10 M x x
• Kw HOH-
• 1.0.10-14 (x) (1.0.10-10 x)

pH - log H pH - log 0.10 pH 1.00
10.00
water
6
Homework (show blank equations, isolate
variable, on problems work down, circle
answers) pg. 703-705 s (dont have to write
solutions for 16, 19, 31, 41)
20 29 32 34 35 37 39a,b 40a,b 42 43a
44c,f
7

• Some Pretty Weak Solutions (read Zumdahls
  inspiring problem solving tips pg. 665)
• Sec 14.5 Calculating the pH of Weak Acid
  Solutions
• When an acid or base exists in an aqueous
  solution, there are ___ equilibria to consider.
  The dissociation of acid or base and the
  _________________ of water.
• (as seen in sample exercise 14.7 b).
• 2. Here, an acid dissociation usually will
  contribute more ___ than water. An example
  would be the dissociation of 1.0 M hydrofluoric
  acid (HF).
• HF(aq) ? H (aq) F- (aq) Ka 7.2.10-4
• H2O (l) ? H (aq) OH- (aq) Kw 1.0 .10-14
• 3. As seen by looking at the K values, water is
  a much _________ acid than HF and under
  conditions of high concentration of acid, waters
  contribution to the H can be neglected.
• Determine the H of the 1.0 M HF solution
• (See pg. 668-669 for tips by the colorful
  arrows-they were purple dots in previous
  editions)
• HF (aq) ? H (aq) F- (aq)
• Initial 1.0 M 0 0
• Final 1.0 M x x x
• Ka HF- / HA
• 7.2.10-4 x2
• (1.0 x) Try to neglect x taken
  from 1.0 M
• x (7.2.10-4)1/2
• x 0.02683 M 0.027M (2.7 of 1.0
  assumption valid)

2
dissociation
H
weaker
8

• Sample exercise 14.8 pg. 669-670
• HOCl (aq) ? H (aq) OCl- (aq)
• Initial 0.100 M 0 0
• Final 0.100 M x x x
• Ka HOCl- / HOCl
• 3.5.10-8 x2
• (0.100 x) Try to neglect x taken
  from 0.100 M
• x (3.50.10-9)1/2
• x 5.916 .10-5 M (0.059 of 0.100
  assumption valid)
• pH - log (5.916 .10-5)
• pH 4.23
• The pH from a mixture of ________ acids. Under
  most conditions (when concentrations of acids are
  nearly equal) consider the _____________ acid to
  be the major contributor of H and neglect other
  equilibrium.
• Sample Exercise 14.9 pg. 670.

weak
stronger
9

• Sample Exercise 14.9
• is the stronger acid.
• Determine H and pH first
• HNO2 (aq) ? H (aq) NO2- (aq)
• Initial 5.00 M 0 0
• Final 5.00 M x x x
• Ka HNO2- / HNO2
• 4.0.10-4 x2
• (5.00 x)
• x (2.00.10-3)1/2
• x 4.472 .10-2 M
• (0.9 assumption OK)
• pH - log (4.472 .10-2)
• pH 1.35

HNO2
HCN(aq) ? H (aq)
CN- (aq) Initial 1.00 M 0.04472 M
0 M Final 1.00 M x 0.04472 M
x x Ka HCN- /
HCN 6.2.10-10 x (0.04472 x)
(1.00 x) neglect x and -x x
(6.2.10-10) / 0.04472 x 1.386 .10-8 M CN-
1.4.10-8 M
10
Homework pg. 703-706 (dont have to write 17)
(hint for 49, both are strong acids-hints in
power point) s 48a,c 49 51 53a 55 61a
62 67
11
Dissociation and Polyprotic Acids

• Percent Dissociation (amount dissociated
  (mol/L) / initial concentration (mol/L)).100
• The more dilute the solution the
  the dissociation.. With a more dilute
  concentration there is less ion pairing.
• Sample Exercise 14.10 pg. 672-673

greater
HC2H3O2 (aq) ? H (aq) C2H3O
2 - (aq) Initial 1.00 M 0 M
0 M Final 1.00 M x
x x Ka HC2H3O2 - /
HC2H3O2 1.8.10-5 x 2 1.00
x neglect x and -x x (1.8.10-5)1/2 x
4.243 .10-3 M dissociation (x / initial
molarity of acid) 100 dissociation 4.243
.10-3 M .100 1.00
M dissociation 0.42
HC2H3O2 (aq) ? H (aq) C2H3O 2 -
(aq) Initial 0.100 M 0 M
0 M Final 0.100 M x x
x Ka HC2H3O2 - /
HC2H3O2 1.8.10-5 x 2 0.100
x neglect x and -x x (1.8.10-6)1/2 x
1.342 .10-3 M dissociation (x / initial
molarity of acid) 100 dissociation 1.342
.10-3 M .100 0.100
M dissociation 1.3
12

• Sample Exercise 14.11

HC3H5O3 (aq) ? H (aq) C3H5O 3 -
(aq) Initial 0.100 M 0 M
0 M Final 0.100 M x x
x Determine x from the dissociation
dissociation x / HC3H5O3o 100 3.7 x
100 (0.100) x 0.00370 M
Now K may be determined K HC3H5O3- /
HC3H5O3 Ka ( 0.00370 )2 / (0.100 - 0.00370
) Ka ( 0.00370 )2 / (0.0963 ) Ka 1.4.10-4

13

• Sec 14.7 Polyprotic Acids (have more than 1
  acidic proton)
• 1. Polyprotic acids dissociate stepwise. Write
  dissociations for Phosphoric acid below. After
  loss of each acidic proton, the subsequent acid
  becomes ____________.
• 2. Usually the first dissociation determine the
  amount of H contributed from the polyprotic
  acid. Exception In ________ solutions of H2SO4
  there are large contributions from the second
  dissociation (HSO4- is a _______ acid). Table
  14.4 pg. 683 shows Ka values for several
  polyprotic acids.
• H3PO4 (aq)? H2PO4- (aq) H (aq) Ka1 H3PO4
  strongest acid
• H2PO4- (aq)? HPO4-2 (aq) H (aq) Ka2
• H2PO4- is an
  species
• HPO4-2 (aq)? PO4-3 (aq) H (aq) Ka3
• PO4-3 is the strongest base
• 
  is an
  amphoteric species
• Ka1gtKa2gtKa3

weaker
dilute
weak
amphoteric
HPO4-2
14

• Sample Exercise 14.15
• First determine H contribution from strongest
  acid (H3PO4).

H3PO4 (aq) ? H (aq) H2PO 4 -
(aq) Initial 5.0 M 0 M 0
M Final 5.0 M x x
x Ka HH2PO4- / H3PO4 7.5.10-3 x2 /
5.0 x try neglecting x x
((7.5.10-3)5.0)1/2 x 0.1936 M (3.9 of
5.0M) H H2PO4- 0.19 M H3PO4 5.0 M
0.1936 M 4.8 M Now analyze the H2PO4-
dissociation
H2 PO4- (aq) ? H (aq) HPO 4 -2
(aq) Initial 0.1936 M 0.1936 M 0
M Final 0.1936 x 0.1936 x x
Ka HHPO4-2 / H2PO4-
6.2.10-8 0.1936 x x
0.1936 x neglect x x HPO4-2
6.2.10-8 M Now analyze HPO4- dissociation
H PO4-2 (aq) ? H (aq) PO 4 -3
(aq) Initial 6.2.10-8 M 0.1936 M 0
M Final 6.2.10-8 x 0.1936 x
x Ka HPO4-3 / HPO4-2 4.8.10-13
0.1936 x x 6.2.10-8
x neglect x x 4.8.10-13(6.2.10-8) / (0.1936) x
PO4-3 1.5.10-19 M
15
Sample Exercise 14.16 Contributions of H from
HSO4- can be substantial in dilute solutions.
H2SO4 is a strong acid (HSO4- is a weak
acid) H2SO4 (aq) ? H (aq) HSO 4 -
(aq) Initial 1.0 M 0 M 0
M Final 0 1.0 M 1.0
M
H SO4- (aq) ? H (aq) SO 4 -2
(aq) Initial 1.0 M 1.0 M 0
M Final 1.0 M x 1.0 M x x
Ka HSO4-2 / HSO4- 1.2.10-2 1.0
x x 1.0 x neglect x x
0.012 M (1.2 of 1.0 so assumption valid)
H 1.0 M 0.012 M pH -log H pH - log
(1.012) pH 0.005 0.01
16

• Sample Exercise 14.17

H2SO4 is a strong acid H2SO4
(aq) ? H (aq) HSO 4 - (aq) Initial 0.0100 M
0 M 0 M Final 0
0.0100 M 0.0100 M
H SO4- (aq) ? H (aq) SO 4 -2
(aq) Initial 0.0100 M 0.0100 M 0
M Final 0.0100 M - x 0.0100 M x x
Ka HSO4-2 / HSO4- 1.2.10-2 (0.0100
x) x (0.0100 x) cant come
close to neglecting x, quadratic must be
utilized x2 0.022 x 0.00012 0 x (- 0.022
/- ((0.022)2 4(0.00012))1/2) / 2 x 0.004524
M H 0.0100 M 0.004524 M 0.014524 M pH
-log H pH - log 0.014524 pH 1.840
17

• The Perils of M1V1 M2V2
• (we have to understand dilution, its not merely
  placing numbers into an equation mindlessly)
• look at problem 49 I will use an analogy
• 1. Consider a building that houses 50 rooms with
  50 women / room.
• How many people will the building hold?
• 50 rooms (50 people / room) 2500 people
• 2. Consider an adjoining building with 150 rooms.
  This building houses 100 men / room.
• How many people will this building hold?
• 150 room (100 people / room ) 15000 people
• 3. A wall between the 2 buildings is knocked out
  and the people are allowed to share the space.
  How many people will there be in each room?
• 15000 people 2500 people 17500 people
• 17500 people / 200 rooms 87.5 people per room
• People represent strong acid particles, rooms
  represent volume (mL).
• Say every person wore a coat to the building and
  took it off when they entered a room. How many
  coats per room would there be?
• 87.5 coats per room because every person has a
  coat
• (88 per room when rounded) The coats could
  represent H ions.
• How many women are there per room? How many
  men per room?

18

• look at problem 50 similar analogy
• 1. Consider a building that houses 90 rooms with
  50 women / room.
• How many people will the building hold?
• 90 rooms (50 people / room) 4500 people
• 2. Consider an adjoining building with 30 rooms.
  This building houses 80 men / room.
• How many people will this building hold?
• 30 room (8 people / room ) 2400 people
• 3. The 2 buildings merge to make a new company
  and buy a new 1000 room office to share equally.
  How many people will there be per room?
• 4500 people 2400 people 6900 people
• 6900 people / 1000 rooms 6.9 people per room
• People represent strong acid particles, rooms
  represent volume (mL).
• Say every person wore a coat to the building and
  took it off when they entered a room.
• How many coats per room would there be?

19
Homework pg. 704-707 Day 1 57 63a,b (dont
have to write answers to 63d,e) 64a 65 70 93
97 (Bonus 69) Day 2 46 50 56 61b 66 94
96 (Bonus 98)
20

• Just Making Sure To Touch All Bases
• Sec 14.6 Bases
• 1. Alkali metal hydroxides are considered
  _________ bases because they are completely
  soluble in water (ionizing completely) in
  releasing ____ ions. When a 1.0 M NaOH solution
  is prepared, the concentration of OH- is ______.
• 2. Alkaline earth metal hydroxides (Ba(OH)2 and
  Ca(OH)2 yield ___ moles of OH- per mole of metal
  hydroxide. These hydroxides have ____ solubility
  in water but act as strong bases (due to the
  presence of OH-) when reacting with acids. Due
  to this low solubility, they are often used in
  ________________ to prevent damage to stomach
  linings.
• Sample Exercise 14.12 pg. 677

strong
OH-
1.0 M
2
low
antacids
pH of 0.050 M NaOH ? NaOH (aq)?
Na(aq) OH- (aq)
Initial 0.050 M 0 M 0 M
Final 0 M
0.050 M 0.050 M OH- 0.050 M pOH -log
OH- pOH - log 0.050 pOH 1.3010 pH 14.00
- pOH pH 14.00 1.3010 pH 12.70
21
acceptors

• 3. Many bases (proton ______________) do not
  contain hydroxide ion. See pg. 678.
• Here the base removes a ___ ion from water,
  leaving an ______ ion.
• Write the reaction of ammonia in water below.
  Label the acid/base and conjugate acid/base
• Example 14.13
• base acid c. acid
  c. base
• NH3 (aq) H2O (l) ? NH4 (aq) OH-
  (aq)
• Initial 15.0 M 0
  0
• Final 15.0 M x x
  x
• Sec 14.8 Acid-Base Properties of Salts
• 1. Recall __________ compounds are called salts.
  When some salts are dissolved in water, they may
  act as an acid or base.
• 2. Salts of strong acids (such as NaCl, NaNO3,
  NaClO4), produce __________ solutions when
  dissolved in water. These anions are extremely
  _______ conjugate bases.
• 3. Salts of weak acids (NaF, NaC2H3O2) act as
  __________ when dissolved in water. The Kb for
  the base is equal to the _________ of Kw and Ka
  of the conjugate acid. Kw Ka. Kb . see pg.
  688.

OH-
H
Kb NH4OH-
NH3 Kb x2 / (15.0 x) x (1.8.10-515.0)1/2
x 0.01643 M
pH 14.00 - pOH pH 14.00 log OH- pH
14.00 log 0.01643 pH 14.00 -1.7843 pH
12.22
ionic
neutral
weak
bases
quotient
Ammonium salts (NH4) act as acids
Al3 ions act as acids as well (See sample
exercise 14.1e)
22

• Sample Exercise 14.18 pH ? of 0.30 M
  NaF Ka of HF 7.2.10-4
• NaF (aq)? Na(aq) F- (aq)
• Initial 0.30 M
  0 M 0 M
• Final 0 M
  0.30 M 0.30 M (F- is a weak base)
• F- the conjugate base of the weak acid
• F- (aq) H2O (l) ? HF (aq) OH- (aq)
• Initial 0.30 M 0 M
  0 M
• Final 0.30 M -x
  x x
• Kb HFOH- / F-
• 1.389.10-11 x2 / 0.30 x (neglect x)
• x (0.30(1.389.10-11))1/2
• x OH- 2.041.10-6 M
• pH 14.00 log OH-
• pH 14.00 log (2.041.10-6)
• pH 14.00 (-5.6902)
• pH 8.31

HF
Kb Kw / Ka Kb 1.0.10-14 / 7.2.10-4 Kb
1.389.10-11
23

• 4. Salts of weak bases act as when
  dissolved in water (Ka Kw / Kb of conjugate).
• Sample Exercise14.19 pH ? of 0.10 M NH4Cl
  Kb (NH3 1.8.10-5)
• NH4Cl (aq)? NH4 (aq) Cl- (aq)
• Initial 0.10
  M 0 M 0 M
• Final 0 M
  0.10 M 0.10 M (NH4 is a weak
  acid)
• NH4 (aq) H2O (l) ? NH3 (aq) H3O (aq)
• Initial 0.10 M 0
  M 0 M
• Final 0.10 M -x
  x x
• Ka NH3H / NH4
• 5.556.10-10 x2 / 0.10 x (neglect x)
• x (0.10(5.556.10-10))1/2
• x H3O 7.454.10-6 M
• pH -log H3O
• pH - log (7.454.10-6)
• pH 5.13

acids
Ka Kw / Kb Ka 1.0.10-14 / 1.8.10-5 Ka
5.556.10-10
24

• Sample Exercise14.20 pH ? For 0.010 M AlCl3
  Ka (Al(H2O)63 1.4.10-5)
• AlCl3 (aq) ? Al3(aq) 3 Cl- (aq)
• Initial 0.010
  M 0 M 0 M
• Final 0 M
  0.010 M 0.030 M
• Most metal cations dont act as acids, Al3 does
• (Al3 is a weak acid when it is hydrated by 6
  water molecules)
• Al(H2O)63 (aq) ? H (aq) Al(H2O)5OH 2 (aq)
• Initial 0.010 M 0 M
  0 M
• Final 0.010 M -x
  x x
• Ka H Al(H2O)5OH2 / Al(H2O)63
• 1.4.10-5 x2 / 0.010 x (neglect x)
• x (0.010(1.4.10-5))1/2
• x H 3.742.10-4 M (3.7 of 0.010 M
  assumption OK)
• pH -log H
• pH - log (3.742.10-4 )
• pH 3.43

NH4F for an example
acidic
basic.
25
Acid Base Oxides

• 1. Non-metal oxides produce
  in water.
• SO2(g) H2O (l) ?
  H2O (l) ? HNO3 (aq)
• 2. Metal oxides produce
  in water.
• CaO (from CaCO3)used in scrubbers
• CaO (s) H2O (l) ?
• H2O (l) ?NaOH (aq)

acids
H2SO3 (aq)
N2O5 (g)
unbalanced
N2O5 (g) H2O (l) ? 2 HNO3 (aq)
balanced

hydroxides
Ca(OH)2 (aq)
Na2O (s)
unbalanced
Na2O (s) H2O (l) ? 2 NaOH (aq)
balanced
26
Homework pg. 704-708 Day 1 (25 73 111 (dont
have to write the answer)) 75a.b 81 85b 101
105b 135 Day 2 (99 101 117 (dont have to
write the answer)) 75c,d 82 89a 100 102
104 106a 107 109 112 118 Day 3 77a,b 83
86a 89b 91 105a 106b.c Also 1. What is the
acidic anhydride of phosphorus acid? (then, write
and balance the chemical equation) 2.
What is the basic anhydride of lithium hydroxide?
(then, write and balance the chemical equation)