Ebbing16.ppt

8–1
John A. Schreifels
Chemistry 212
Chapter 16-1
Chapter 16
Acids and Bases

8–2
John A. Schreifels
Chemistry 212
Chapter 16-2
Overview
• Acid – Base Concepts
– Arrhenius
– Brønsted – Lowry
– Lewis
• Acid and Base Strengths
– Relative Strengths of Acids and Bases
– Molecular Structure and Acid Strength
• Self – Ionization of Water and pH
– Self – Ionization of Water
– Solutions of a Strong Acid or Base
– The pH of a Solution

8–3
John A. Schreifels
Chemistry 212
Chapter 16-3
Acid – base concepts
• Arhennius Concept:
– acid: provides H+ ions (called a proton) in water.
HA(aq)  H+(aq) + A(aq)
– base: provides OH in water.
• Brønsted–Lowry Concept:
– acid: donates H+.
– base: accepts H+.
• No water or hydroxide required.
– Base converted to its conjugate acid and develops properties that are those
of an acid.
E.g. Identify each as either an acid or base and determine its
conjugate: and , F, H2CO3 and
E.g. Identify the conjugate acids and bases in the reaction below:
• Amphoteric substance: a substance that can act as either an acid or
base. (E.g. H2O in examples)
)
aq
(
OH
)
aq
(
M
)
aq
(
MOH
O
H2 
 

 

)
aq
(
OH
)
aq
(
NH
O(l)
H
(aq)
NH 4
2
3

 



(aq)
NH
)
aq
(
O
H
O(l)
H
)
aq
(
NH 3
3
2
4 


 


3
HCO 
2
3
CO 
4
HPO

8–4
John A. Schreifels
Chemistry 212
Chapter 16-4
Acid – base concepts 2
• Lewis acid: electron pair acceptor
• Lewis base: electron pair donor. .
• Lewis definition most general, then Brønsted-Lowery
and finally Arhennius:
• E.g.
• E.g.2 determine the Lewis acid and base in BF3 and
NH3 in the reaction:
• E.g.3 determine the Lewis acid and base in the
following reaction:
Co3+(aq) + 6F(aq)  [CoF6]3.
(aq)
NH
)
aq
(
O
H
O(l)
H
)
aq
(
NH 3
3
2
4 


 


 

 2
3
3 )
NH
(
Ag
)
aq
(
NH
2
)
aq
(
Ag
3
3
3
3 BF
NH
BF
NH 



8–5
John A. Schreifels
Chemistry 212
Chapter 16-5
Acid/Base Strength
• Extent of acid/base
reaction variable and
depends upon the
relative strengths of the
acids and conjugate
bases..
• Strong acids and bases
react with other reactant
to produce all product.
Common Strong Acids
and Bases
Acids Bases
HClO4 LiOH
H2SO4 NaOH
HI KOH
HBr Ca(OH)2
HCl Sr(OH)2
HNO3 Ba(OH)2
Stronger acids and
bases react to form
weaker conjugate
bases and acids.
)
aq
(
A
)
aq
(
O
H
)
l
(
O
H
)
aq
(
HA 3
2

 



)
aq
(
Cl
)
aq
(
O
H
)
l
(
O
H
)
aq
(
HCl 




 3
2

8–6
John A. Schreifels
Chemistry 212
Chapter 16-6
Relative Strengths of Acids and Bases and Extent of
Reaction
• The table of relative
strengths of acids and
conjugate bases can be
used to predict if a reaction
will produce product.
E.g. Which will produce
product?
HNO3 + CN or HCN + 
3
NO









ClO
HS
S
HClO
HNO
F
NO
HF
or
or
2
3
3

8–7
John A. Schreifels
Chemistry 212
Chapter 16-7
Factors Affecting Acid Strength
• Binary acids:
– Bond strength is directly related to the acid strength (bond size).
• HI and HBr have larger bonds lengths and are more acidic than
HF and HCl, even though fluorine is most electronegative.
– For bonds of similar size the acid strength is related to
electronegativity difference.
E.g. bonds across a row more acidic towards right side of periodic
table.
• Oxyacids are acidic substances that contain oxygen and some
other nonmetal, e.g. HNO3, HOCl, etc.. Anything that affects the
polarity of the O–H bond will affect the strength of the acid.
– An increase in the electronegativity of an atom bound to oxygen
increases in polarity of the bond and makes it more acidic.
– More oxygen = more polar.
E.g. determine relative acidity of HOI, HOBr and HOCl.
E.g. HClO4 is strongest acid in its oxyacid series.

8–8
John A. Schreifels
Chemistry 212
Chapter 16-8
Autoionization of Water
• Water can act as both an acid and a base equilibrium is:
H2O + H2O  H3O+ + OH. Kw = [OH][H3O+] = 1.00 x 1014M2.
• Since [OH] = [H3O+] [H3O+] = 1 x 107 M (called a neutral
solution)
– Acidic [H3O+] > 1.00x107M
– Neutral [H3O+] = 1.00x107M
– Basic [H3O+] < 1.00x107M
• All acids/bases dissolved in water must obey equation for the
ionization of water.
– They either add H3O+ or OH to water.
• Most of the acids in this chapter will be stronger than water and
add significantly to the hydronium ion concentration.
E.g. the hydronium ion concentration of an acidic solution was
1.00x105 M. What was the [OH]?
• E.g. what is the hydronium ion concentration if the hydroxide
concentration was 2.50x103 M?

8–9
John A. Schreifels
Chemistry 212
Chapter 16-9
Strong acids and Bases
• A strong acid is completely dissociated in water. This leads to
[H3O+] and [OH].
Eg: Calculate the [H3O+],[OH] and [Cl] for a 0.048 M HCl
solution. Assume the contribution from water is negligible.
E.g.2 Calculate the conc. of all ionic species as well as the pH if
CNaOH = 0.080 M.
E.g. 3 what is pH and [OH] of 0.125 M Ba(OH)2.
• [H3O+] of water is small compared to added [H3O+] from the acid
and ignored in the calculation.
• A more rigorous treatment is:
– The last term is very small except when the concentration of the
strong acid is very small.
– When the concentration of added acid is small compared with
pure water, include the contribution from water.
E.g.4 estimate the [H3O+] of 108 M HCl.
O
H
3
SA
3
total
3 2
]
O
H
[
]
O
H
[
]
O
H
[ 

 


8–10
John A. Schreifels
Chemistry 212
Chapter 16-10
The pH of a Solution
• pH = log[H3O+] and [H3O+] = 10pH
– Acidic pH < 7.00
– Neutral pH = 7.00
– Basic pH > 7.00
E.g. determine the pH of a solution in which [H3O+] = 5.40x106 M
E.g.2 determine the pH of a solution in which the [OH] = 3.33x103 M
E.g.3 determine the pOH of a solution in which the [OH] = 3.33x103 M
E.g.4 Determine the [H3O+] if the pH of the solution is 7.35.
• The term pX is defined in exactly the same way as pH.
Eg.5 What is the pCa if [Ca2+] = 6.44x10-4
[H3O+
][OH
] = 1.00x1014
log{[H3O+
][OH
]} = log{1.00x1014
}
pH + pOH = pKa
= 14.00

8–11
John A. Schreifels
Chemistry 212
Chapter 16-11
Methods of Measuring pH
• pH paper is used that has compounds in it which are
change to different colors for different pH ranges.
• An colored indicator can be placed in the solution and
its color correlated with pH.
HIn(aq) + H2O(l)  H3O+(aq) + In(aq).
E.g. phenolphthalein is colorless in acid form but pink
in basic form.
– The pH at which they change color depends on their
equilibrium constant.
• More accurate and precise measurements are made
with a pH meter. A combination of voltmeter and
electrodes.

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