Intro to Acids & Bases
Properties of Acids & Bases
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Acids
Taste sour
Reacts with metals
Turns litmus red
Conducts electricity
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Base
Taste bitter
Slippery
Turns litmus blue
Conducts electricity
Ions in Solution
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Acidic solutions – contain more H+ than
OHBasic solutions – contain more OH- than
H+
Neutral solutions – contain equal
amounts of H+ and OH-
Autoionization of Water
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H2O + H2O  H3O+ + OHWater is the usual solvent for acids and
bases
It produces equal numbers of H3O+ and
OH-
Arrhenius Model of Acids & Bases
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Acid: a substance that contains H and
ionized to produce H+ when dissolved in
water.
Base: a substance that contains OH and
ionizes to produce OH- when dissolved in
water
Arrhenius Model of Acids & Bases
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HCl  H+ + ClHCl contains H and ionizes to form H+
This could be an Arrhenius acid
NaOH  Na+ + OHNaOH contains OH and ionized to form
OHThis could be considered an Arrhenius
base
Arrhenius Model of Acids & Bases
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Although the Arrhenius model is useful in
describing many acids and bases, it does
not describe them all
For example NH3 contains no OH- ions, but
it is a base
A model to describe all bases is needed
Bronsted-Lowry Model
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Acid: proton donor
Base: proton acceptor
HX + H20  H3O+ + XHX donates an H+ to the water molecule
The water takes the H and is there for
considered the base
Bronsted-Lowry Model
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Conjugate acid – the species produced
when a base accepts the H+ ion from the
acid
Conjugate base – the species produced
when the acid gives up its H+
Conjugate Acids & Conjugate Bases
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Identify the acid, base, conjugate acid,
and conjugate base of the following
reaction…
HX + H20  H3O+ + XA
B
CA
CB
Every Bronsted-Lowry interaction involves
conjugate acid base pairs
Conjugate Acids & Conjugate Bases
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Identify the acid, base, conjugate acid,
and conjugate base of the following
reaction…
NH3 + H20  NH4+ + OHB
A
CA
CB
Conjugate Acids & Conjugate Bases
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What did you notice that was different
about the previous two reactions?
Water was an acid in one and a base in
the other
Amphoteric – substance that can act as
either an acid or a base
Conjugate Acids & Conjugate Bases
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Identify the acid, base, conjugate acid,
and conjugate base of the following
reactions…
NH4+ + OH-  NH3 + H20
A
B
CB
CA
HBr + H2O  H3O+ + Br A
B
CA
CB
Neutralization Reactions
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Neutralization reactions – acid + base
 a salt + water
Neutralization reactions are just a special
type of double replacement reactions
Neutralization Reactions
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Write the equations for the following
neutralization reactions
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Acetic acid and ammonium hydroxide
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HCH3COO + NH4OH  HOH + NH4CH3COO
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Nitric acid and cesium hydroxide
HNO3 + CsOH  HOH + CsNO3
The pH Scale
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[H+] is often expressed in very small
numbers. Chemists needed an easier way
to express [H+] ions
pH is a mathematical scale in which the
concentration of hydronium ions in a
solution is expressed as a number from 0
to 14.
pH = -log[H+]
Interpreting the pH Scale
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pH of 7 is neutral. A pH less than 7 is
acidic, and a pH greater than 7 is basic.
pH Calculations
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pH = -log[H+]
pOH = -log[OH-]
pH + pOH = 14
Calculating pH
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What is the pH of a 0.5M HCl solution?
0.5 mol HCl x 1 mol H+ = 0.5M H+
L
1 mol HCl
pH = -log[H+]
pH = -log[0.5]
pH = 0.3
Calculating pH
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Calculate the pH of a 0.0057M HBr
solution.
2.2
Calculating pH
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What if we have a base?
What is the pH of a 0.05M NaOH solution?
0.05 mol NaOH x 1 mol OH- = 0.05M OHL
1 mol NaOH
pOH = -log[OH-]
pOH = -log[0.05]
pOH = 1.3
pH + pOH = 14
pH = 12.7
Calculating pH
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Calculate the pH of a 0.000089M KOH
solution.
9.95
Acid/Base Strength
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The strength of an acid or a base tells you
the degree of ionization
Strong acids & bases break down into
many ions
Weak acids & bases break down into just
a few ions
Acid/Base Strength
Strong acids
hydrochloric acid, HCl
hydrobromic acid, HBr
hydriodic acid, HI
nitric acid, HNO3
sulfuric acid, H2SO4
perchloric acid, HClO4
periodic acid, HIO4
Weak acids
acetic acid, CH3COOH
hydrocyanic acid, HCN
hydrofluoric acid, HF
nitrous acid, HNO2
sulfurous acid, H2SO3
hypochlorous acid, HOCl
phosphoric acid, H3PO4
Acid/Base Strength
Strong bases
Weak bases
sodium hydroxide, NaOH
potassium hydroxide, KOH
ammonia, NH3
sodium carbonate, Na2CO3
calcium hydroxide, Ca(OH)2 potassium carbonate,
K2CO3
barium hydroxide, Ba(OH)2 aniline, C6H5NH2
sodium phosphate, Na3PO4
trimethylamine, (CH3)3N