Download weak conjugate base

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Taste sour
Form solution that conduct
electricity
React with metals
Turn blue litmus paper to red
React with bases to form salt and
water
Ex: fruit juice, vinegar, milk
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Form solutions that conduct electricity
Slippery or soapy in the skin
Taste bitter
Turn red litmus paper to blue
Reacts with acids to form salt and water
Ex: soap, shampoo, cleaning agent
Arrhenius Theory
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By Svante August Arrhenius
Acids form hydrogen ion(H+) in aqueous
solutions
Bases form hydroxide ion (OH-)
in aqueos solution
Ex: HCl(g)-----> H+(aq) + Cl-(aq)
KOH -----> K+
+ OH-(aq)
Bronsted-Lowry Denition
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By Johannes Bronsted and Thomas Lowry
Acid is a proton donor
Base is a proton acceptor
Ex:
HCl + H2O ---> H3O + ClNH3 + H2O 
Bronsted-Lowry Definition
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The general reaction when an acid is dissolved in water is best
represented by an acid donating H+ to water molecule to form a new
acid (conjugate acid) and a new base( conjugate base)
acid
Acid
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base
base
conjugate
Conjugate
HA(aq) + H20(l) ----> H3O+(aq) + A-(aq)
Ex:
HCl + H2O ---> H3O+ +
acid
base
conjugate
acid
Clconjugate
base
.
Practice:
Identify the acid and the base in the
following reactions:
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HSO4- + PO43- ---> HPO42- + SO42HNO3 + H2O ---> H3O + + NO3H3PO4 + CN- ---> H2PO4- + HCN
Conjugate Acid-base pair
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Consists of two substances related to each other by donating
and accepting of a single proton
Acid-conjugate base pair
Ex: HCl(aq) + H2O(l)  H3O+ + ClBase-conjugate acid pair
H3O+ --> hydronium ion
Strong Acids
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Bronsted-Lowry definition is useful in describing the
strength of an acid
Strong acid is one that dissociates or ionizes
completely in water
Ex:HCl + H2O  H3O+ + ClForward reaction predominates which indicates ionization is
complete
Strong acid contains a weak conjugate base weaker than water
Weak Acid
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It does not completely dissociate or ionize.
Ex: Acetic Acid( CH3COOH)
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CH3COOH + H2O
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H30+ + CH3COOacetate ion
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The two arrows indicate that the ionization is not
complete
The reverse reaction predominates that means
only few ions are dissociated
Weak acid contains relatively strong conjugate
base
Strong Bases
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Common strong bases are those that contain the
hydroxide ion
Ex:,NaOH,KOH Mg(OH)2, Ca(OH)2
Ba(OH)2
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Very soluble in water
Weak Bases
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The strengths of bases that do not have OH- are
described in the same way that the strengths of the
acids were described
Weak base does not completely dissociate in water
Ex: NH3 + H2O
NH4+ + OHreverse reaction predominates
Acid Strength
Strong
Acid
Strong
Base
Moderate
Acid
Weak
Acid
Weak
Base
HClO4
NaOH
H3PO4
CH3COOH
NH3
HClO3
KOH
Moderate
Base
H2CO3
HCO3-
HI
Mg(OH)2
CO32-
H3BO3
CH3COO-
HBr
Ca(OH)2
CH3COOH
SO42-
Ba(OH)2
Sulfuric acid
Very Weak
Acid
Very Weak
Base
HCl
H2O
H2O
Perchloric acid
Phosphoric acid
Chloric Acid
Hydrobromic
H2SO4
Hydrochloric
HNO3
Nitric Acid
Water as an acid and a base
Amphoteric substance
 A substance that can behave either as an acid or a base
 Ionizaton of water
 H2O(l) + H2O(l) ---> H3O+(aq) + OH-(aq)
 The forward reaction is not great
 In pure water only a tiny amount of H3O+ and OH- is present.
 [H3O+] = [OH-] = 1.0x10-7M
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The product of the H3O+ and OH- concentrations is always
constant at 250C
[H3O] [OH-] = 1x 10 -14
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(1x 10-7 ) ( 1 x 10-7) = 1 x 10-14
This is called the ion product constant of water ( Kw)
 Note the product of H3O and OH- in any aqueous is constant which
means when [OH-] goes up the [H3O] must go down
 Acidic solution  [H+] > [OH-]
 Basic solution  [ H+] < [OH-]
 Neutral solution  [H+] = [OH-]
Ex : calculate [H+] or [OH-] as required for each of the
following at 250C and state whether the solution is
acidic, basic and neutral
A) 1.0x10-5M OHGiven: [OH-] = 1x10-5
Find: H+
Solution: [H+] [OH-] = 1x10-14
[H+] = 1x10-14
[OH-]
[H+] = 1 x 10-14
[ 1x10-5]
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=
1x 10-9 M
Since OH- = 1x10-5M
H+ = 1x10-9M
The solution is basic since OH- > H+
b) 10.0M H+
Find: OHSolution: [H+][OH-] = 1 x10-14
[OH-] = 1x 10-14
10.0M
= 1x 10-15M
[OH-] = 1x10-15
[H+] = 1x 101M
[H+] > [OH-] = the solution is acidic
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The pH Scale
Was proposed by Soren Sorensen
( Danish biochemist)
 pH means power of hydrogen
 Has a range from 0 to 14 and is logarithmic
which means that each step is ten times the
previous
Ex: pH of 5 is ten times more acid than 6
What about pH 5 and 7
---> pH 5 is 100times more acid than 7
What about pH 5 and 8?
 1000 times acidic
pH scale
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0-most acidic and 14 is most basic
0
1
2
3
4
5
6
7
8
9
10 11 12 13
14
At pH-7, water has equal amount of H+ and OH- ions
[H+] = [OH-]  neutral
[H+] > [OH-] acidic
[H+] < [OH-] basic
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pH of a solution
Defined is the negative of the logarithm
of the hydronium ion concentration,
[H3O+]
pH = - log [H3O+]
Ex: Pure water has [H3O+]= 1x10-7M. Find
pH
pH = -log[H3O+]
pH = -log[ 1x10-7M]
pH = - (-7)
pH = 7
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In Basic solution,
[OH-] can be expressed as pOH
 pOH = -log [OH-]
Recall that [H3O+] [OH-] = 1 x 10 -14
Using the definition of pH and pOH the
equation can be translated as
pH + pOH = 14
In summary,
pH= -log[H3O+]
pOH = -log [OH-]
[H3O+][OH-] = 1x10-14
pH + pOH = 14
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Ex:
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Find the pH and pOH of 0.001MHCl solution
Given: [H3O+] = 0.001M
Find a) pH b) pOH
Solution
A) pH = -log [H3O+]
= -log [ 1x10-3] = -(-3)
=3
B) pH + pOH = 14
pOH = 14 - pH
= 14 - 3
11
Ex2:
If the OH- is equal to 0.00001M, Find the pH
Solution: Get the pOH first
pOH=-log[OH-]
= -log(10-5M)
= -(-5)
pOH = 5
Get the pH
pH +pOH = 14
pH = 14 – pOH
= 14 – 5
pH = 9
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Indicators
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Substances that exhibit different colors in acidic
and basic solutions. It has a weak acid(conjugate
acid) has a color, and its conjugate base has
another color
HInd(aq) + H2O
H3O+ + IndConjugate
acid
conjugate
base
Are usually used in solutions like
phenolphthalein while others used in a form of
strips called pH paper , and litmus paper
Phenolphthalein: in acid colorless
in base  pink
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Some Indicators
Indicator
pH interval color
Color change
phenolpthalein
8.3 - 10
Colorless - pink
Methyl orange
3.1 – 4.4
Red - yellow
Bromcresol
green
3.8 – 5.4
yellow- blue
Phenol red
6.4 – 8.2
yellow- red
Thymolpthalein
9.4 to 10.6
Colorless- blue
Litmus paper
4.5 – 8.2
Red to blue
Buffer Solution
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One that contains a weak acid and its conjugate
base, or a weak base and its conjugate acid
Has a remarkable property of maintaining an
constant pH even though a strong acid or a base
is added to the solution
The pH of biological fluids is maintained by
buffers.
Ex: blood is heavily buffered by
Note:
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Buffers has a remarkable property of
maintaining an almost constant pH even with
the addition of a strong base or acid due to
the presence of the weak acid that
neutralizes any added base and also a weak
base that neutralizes any added acid.
Example
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A solution with 1.0M CH3COOH(acetic acid), and
1.0M in NaCH3COO( sodium acetate)base. The acid
will react with any added base as follows:
CH3COOH + OH- ---> H2O + CH3COO The base will react with any added acid (H3O+)
 CH3COO- + H3O+  H2O + CH3COOH
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Neutralization Reaction
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occurs between an acid and a base
producing equal amounts of H3O+ and
OHChemical reaction that forms water and
salt
Occurs between
Strong acid and strong base
A weak acid and a strong base
A weak acid and a weak base
Neutralization
Occurs when an equivalent amount of an acid reacts with an
equivalent amount of a base
HCl + NaOH ----> NaCl + H2O
neutral solution
This process is accomplished by means of titration
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Neutralization Reaction
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Acid and base properties combine to form
water
H+
+ OH- -------> H2O
Note: water is one of the products of
neutralization reaction
Acid Base Titration
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Is a useful application of neutralization reaction
A process of adding a solution of accurately known
concentration, standard solution, ( titrant) to another
solution of unknown concentration,( analyte until the
chemical reaction between the two is complete ( the
equivalence point) or end point
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Equivalence point is the point in titration where the
indicator used undergoes a color change
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Note; indicator changes color at pH=7
At the equivalence point,
n Acid = n base,
to get the molarity of the base or acid
M = n = moles
V
L
M acid = n acid
V acid
,
nA = n B
MAVA = MBVB
M base =
n bas
Vbase
Ex:
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In a titration, It takes 6mL of 0.5MNaOH to
neutralize 15mL of HCl. What is the concentration of
HCl?
NaOH + HCl -----> NaCl + H2O
molar ratio ( 1:1)
MA VA = MBVB
MA = MBVB = (0.500M)(6mL)
VA
15mL
= 0.2M
Sample 2
A 25.0mL of sulfuric acid solution requires 32.58mL of .500M
NaOH to neutralize it. What is the molarity of H2SO4?
Solution:
1.Write the balance equation
H2SO4 + NaOH --->
H2SO4 + NaOH ---> Na2SO4 + H2O
H2SO4 + 2 NaOH ---> Na2SO4 + 2 H2O
2mole NaOH : 1 mole H2SO4
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2.Determine the number of moles of NaOH
M = n , n = MV n = (0.500moles) ( 0.03258L) = 0.01629 moles
V
L
3.Determine the molarity of H2SO4 using nA = nB
M = n , M = 0.01629moles NaOH x 1mole H2SO4
V
0.025L
2mole NaOH
M H2SO4 = 0.3258M