ACIDS AND BASES AND PH
Chemistry
Acids and Bases
Properties and pH
Chemical Warfare!
What is an Acid?

3 Major Definitions: Arrhenius, Bronsted-Lowry, and
Lewis.
 Arrhenius
and Bronsted-Lowry say an acid is:
A proton donor
 What is a proton?
A proton = H+
H + = H3O +
Acid and Base Strength

Acids and bases are
considered “strong” or “weak”
depending on how much they
dissociate
 The
more something dissociate,
the stronger acid or base it is.
 This means we are looking at
the amount of H+ or OH- is in the
solution
Ionization of HCl and formation
of hydronium ion, H3O+
H2O +
Proton
acceptor
HCl
Proton
donor

H3O+ + Cl-
Strong Acids vs. Weak Acids
Strong acids are assumed to be 100%
disassociated in solution (good proton donors).
Are Strong Electrolytes
HCl
H2SO4
HNO3
Weak acids are usually less than 5%
disassociated in solution (poor proton donors).
Are Weak Electrolytes.
H3PO4
HC2H3O2
Strong Acid Dissociation
Weak Acid Dissociation
Arrhenius & Bronsted-Lowry Acids=
Proton Donors
Monoprotic acids
Diprotic acids
HCl
H2SO4
HC2H3O2
H2CO3
HNO3
Triprotic acids
H3PO4
Properties of Acids
 Acids taste sour
 Acids effect indicators
 Blue litmus turns red
 Methyl orange turns red
 Acids have a pH lower than 7
 Acids are proton (hydrogen ion, H+) donors
 Acids react with active metals, produce H2
 Acids react with carbonates, produce CO2
 Acids neutralize bases
Sulfuric Acid
 Highest volume production of any
chemical
 Used in
 Used in
 Used in
in the U.S.
the production of paper
production of fertilizers
petroleum refining
Nitric Acid
• Used in the production of
fertilizers
• Used in the production of
explosives
• Nitric acid is a volatile acid
– its reactive components
evaporate easily
• Stains proteins (including
skin!)
Hydrochloric Acid
• Used in the pickling of
steel
• Used to purify magnesium
from sea water
• Part of gastric juice, it
aids in the digestion of
protein
• Sold commercially as
“Muriatic acid”
Phosphoric Acid
o A flavoring agent in sodas
o Used in the manufacture
of detergents
o Used in the manufacture
of fertilizers
o Not a common laboratory
reagent
Acetic Acid
Used in the manufacture of
plastics
Used in making
pharmaceuticals
Acetic acid is the acid
present in vinegar
Acids Effect Indicators
Blue litmus paper turns red in contact
with an acid.
Acids Have
a pH less
than 7
Acids React with Active Metals
Acids react with active metals to form
salts and hydrogen gas.
Mg + 2HCl  MgCl2 + H2(g)
Acids did not react with Copper, because
copper is not an “Active Metal”
Acids React with Carbonates
2HC2H3O2 + Na2CO3
2 NaC2H3O2 + H2O + CO2
Effects of Acid Rain on Marble
(calcium carbonate)
George Washington:
BEFORE
George Washington:
AFTER
What is a Base?


3 Major Definitions: Arrhenius, Bronsted-Lowry, and
Lewis.
Arrhenius Base increases OH- concentration when in
solution.
 NaOH
 Na+

& OH-
Bronsted-Lowry Bases are proton (H+) acceptors.
 NH3

when disassociated produces:
+ HCl  NH4+ + Cl-
An Arrhenius base is always a B-L Base, but a B-L
base is not always an Arrhenius base.
Properties of Bases
 Bases taste bitter
 Bases effect indicators
 Red litmus turns blue
 Phenolphthalein turns purple
 Bases have a pH greater than 7
 Bases are proton (hydrogen ion, H+) acceptors
 Solutions of bases feel slippery
 Bases neutralize acids
Examples of Bases




Sodium hydroxide (lye), NaOH
Potassium hydroxide, KOH
Magnesium hydroxide, Mg(OH)2
Calcium hydroxide (lime), Ca(OH)2
Strong Bases vs. Weak Bases
Strong bases are assumed to be 100%
disassociated in solution.
Are strong electrolytes!
NaOH
Ca(OH) 2
Weak acids are usually less than 5%
disassociated in solution.
Are Weak electrolytes!
Cu(OH)2
NH3
Strong Base Dissociation
NaOH
Na+
OH-
Weak Acid Dissociation
AgOH
AgOH
Ag+
OH-
Bases Effect Indicators
Red litmus paper turns blue
in contact with a base.
Phenolphthalein
turns purple in a
base.
Bases have
a pH
greater
than 7
Is H2O an acid or base?

HCl + H2O  H3O+ + Cl H2O

NH3 + H2O  NH4+ + OH H2O

is an base! = proton acceptor
is an acid! = proton donor
H2O can be either. This is called
 Amphoteric
= can act like an acid or base.
Ion Concentration in Water
pH- what is it?


pH is a measure of the H+ or H3O+ concentration.
The higher the concentration of H+ or H3O+ , the
lower the pH.
have higher [H3O+], than pure water
 pH range of an acid is 0 - 6.99.
 pH of pure water is 7
 Acids
pOH- what is it?


pOH is a measure of the OH- concentration.
The higher the OH- concentration, the lower pOH.
 Bases

have higher OH- concentrations than pure water.
pH and pOH are exact opposites!
 In
a solution:
the [H3O+] increases, [OH-] decreases
 when pH increases, pOH decreases
 when
pH explained
Self-Ionization of Water
H2O + H2O

H3O+ + OH-
H+, OH-, and pH
pH
Scale
How Do You Determine?

Described by an ionization equation:
HCl(aq)→ [H]+ + [Cl]–

Each acid and base will have either a high or low
percent ionization
 i.e.
a high or low amount of the solution which
dissociates into ions
 The higher the percent ionization the stronger the acid
pH

The pH is defined according to
the following formula:
pH = -log[H+]
and [H+]=10-pH

where [H+] represents the
concentration of hydrogen ions
in mol/L
pOH

The pOH is defined according
to the following formula:
pOH = -log[OH-]
and [OH-]=10-pOH

Also note that pH + pOH= 14
pH and pOH is logarithmic


The pH and pOH scale is
logarithmic, just like the
Richter scale for
earthquakes!
So a change of 1 pH
means the concentration
has changed by a factor of
10!
Acid and Base Strength
For bases, a solution with a pH of 13 is:
10 times more basic than a solution with a pH of 12
100 times more basic than a solution with a pH of 11
For acids, a solution with a pH of 3 is:
10 times more acidic than a solution with a pH of 4
100 times more acidic than a solution with a pH of 5
Measuring pH with wide-range paper
Narrow-Range pH Paper
How Else Can We Measure Strength?


Scientists use a pH scale to represent how acidic or
basic a solution is
pH means "power of hydrogen”
Practice Problems
What is the pH of a 1.2 x 10-3 HBr solution?
What is the pOH of a 1.2 x 10-3 HBr solution?
Practise Problems


What is the [H+] concentration in a solution with a
pH of 7?
What is the [OH-] concentration in a solution with a
pH of 12?
Indicators

The most common method
to get an idea about the
pH of solution is to use an
acid base indicator
 An
indicator is a chemical
that changes colour
depending on the pH

A variety of indicators
change color at various pH
levels
Litmus paper


The most common indicator is found on "litmus"
paper
It is red below pH 4.5 and blue above pH 8.2
Phenolphthalein


Phenolphthalein is a most common liquid indicator
It is clear below pH 8.5 and pink above pH 8.5
Other Indicators

Can also be obtained from many natural sources
like strawberries, cabbage, tea and tulips
OTHER Tools


Basic indicators only show
if a substance is acidic or
basic, but not strength
 Universal indicator are
a mixture of indicators
and can show strength
of acid or base
So can a pH Meter