Acid and Base Reactions
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Acid and Base Reactions
Definitions of acids and bases
Svant Arrhenius (Sweden) 1859-1927
Johannes Bronsted (Denmark) 1879-1947
G. N. Lewis (U.S.) 1875-1946
dissolves in water to yield protonsH—X H+
(aq) + X–(aq)
dissolves in water to yield hydroxideions
Y—OH Y+ (aq) + HO–
(aq)
Arrhenius definitions of acids
A base
An acid
and bases
Bronsted Definition
An acid is a proton donor
A base is a proton acceptor
An acid is a proton donor
an example is HCl
a source of hydronium ion (H3O+ )
HC
Proton transfer from HCl to water.
hydronium ion
Cl ::
:HO
H
H
:: O
H
H: H
+Cl :
::
:
A base is a proton acceptor
an example is NaOH
a source of hydroxide ions ( OH- )
HC√
A base is a proton acceptor
Cl ::
:HO
H
::
: O
H
H: : Cl :
::
:
Ammonia is a Bronsted base
OH:
:H
hydroxide ion
:N
H
H
H
O H
:::
HN
H
H
H+
A Weak Base
Acid-Base Neutralization
Acid + Base Salt + Water
Neutralization
Example of Neutralization
Complete ionic equation
HCl(aq) + NaOH(aq) NaCl(aq) + H2O (l )
Na+(aq) + Cl–(aq) + H2O(l)
Na+(aq) + OH–(aq) + H+(aq) + Cl–(aq)
Cancel Spectator ions
Acid + Base Salt + Water
OH–(aq) + H+(aq) H2O(l )
Net ionic equation
Bronsted Definition
An acid is a proton donor
A base is a proton acceptor
Conjugate acid-base pair
Conjugate Acids and Bases
• Reactions between acids and bases always yield their conjugate bases and acids.
Consider the transfer of a proton from HCl to water.
Cl ::
:HO
H
H
:: O
H
H: H
+Cl :
::
:
acidbase Conjugate base
Conjugate acid
Acetic acid
CH3COH
O
+ H2O CH3CO– + H3O+
O
acid base Conjugate base
Conjugate acid
Practice Exercise
: :CN O
H
H
::
acidbase
:CNH O
H
: ::
Conjugate base
Conjugate acid
Identify the conjugate acid-base pairs for the reaction
Equilibrium constant for proton transfer
Cl :
::
HO
H
H
:: O
H
H: H
+Cl :
::
:
[H2O]
[H3O+]
[HCl]
[Cl-] [H3O+]
[HCl]
[Cl-]K =
[H+]
[HCl]
[Cl-]K =
The Acid - Base Properties of Water
Water as an Acid and a Base
acidbase
O
H
H
::
:
O
H
:H O
H
H: H
+O
H
::
:
Conjugate base
Conjugate acid
Ion Product of Water ( Kw )
The equilibrium constant for the ionization of water into H+ and OH- ions
Ion Product of Water ( Kw )
acidbase
O
H
H
::
:
O
H
:H O
H
H: H
+O
H
::
:
Conjugate base
Conjugate acid
= [ H3O+] [ HO- ]
= 1.0 x 10-14
Kw = [ H+] [ HO-]
= 1.0 x 10-14Kw = [ H+] [ HO-]
[ H+] = [ HO-]Neutral solution:
= 1 x 10-7 M
[ H+] > [ HO-]Acidic solution:
[ H+] < [ HO-]Basic solution:
Practice Exercise
Calculate the concentration of HO- ions in a hydrochloric acid solution whose hydrogen ion concentration is 1.3 M.
Kw = 1 x 10-14 = [ H3O+] [ HO-]
1 x 10-14 = ( 1.3 ) [ HO-]
7.7 x 10-15 M = [ HO-]
pH: A Measure of Acidity
The pH Scale
pH = - log10 [ H+]
The pH of a neutral solution is 7 at 25ºC
pH = - log ( 10-6 )
solutions have pH < 7
= 6
= 8
Acidic
solutions have pH > 7
pH = - log ( 10-8 )
Basic
but we must keep in mind that a difference of 1 pH unit is equivalent to a factor of 10 acidity
the pH scale is useful in that it lets us express acidity by numbers that are not exponentials
thus, a solution with a pH of 2 is not twice as acidic as one with a pH of 4 it is 102 (or 100) times as acidic
pH
pH values of common fluids
pH values of common fluids
pH values of common fluids
Practice Exercise
The pH of a certain fruit juice is 3.33 Calculate [ H+] .
pH = 3.33
log [ H+] = -3.33
[ H+] = 10 -3.33
[ H+] = 4.7 x 10 -4M
= - log10 [ H+]
Acidsand
Bases
Other “p” Scales
• The “p” in pH tells us to take the negative base-10 logarithm of the quantity (in this case, hydronium ions).
• Some similar examples are– pOH: −log [OH−]– pKw: −log Kw
© 2012 Pearson Education, Inc.
Practice Exercise
The OH- concentration of a blood sample is 2.5 x 10-7 M . What is its pH?
pOH = - log10 [ OH-]
pOH = 6.60
= - log [ 2.5 x 10-7 ]
pH = 14 - pOH
pH = 7.40
pH + pOH = 14
The pH Scale
pH = log10 =
[ H3O+]
1= log10
[ H+]
1
pH = - log10 = [ H3O+]= - log10[ H+]
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