Chapter 15: Acids & Bases
Properties of Acids & Bases
Acids
1.
2.
3.
4.
5.
Aqueous solns of acids have a
SOUR taste.
Has many indicators but most
common is LITMUS PAPER… turns
Blue to Red
Some acids react with metals to
release H2 gas
Acids react with Bases to produce
salts & H2O (neutralized soln)
Some acids conduct electric
currents
Bases
1.
2.
3.
4.
5.
6.
Aqueous soln tastes bitter
Bases have many indicators but
most common is LITMUS
PAPER… turns Red to Blue
Bases do not react with metals
React with acids to produce salts
& H2O
Bases conduct electric current
Dilute aq soln of bases feel
slippery
Acid Nomenclature
Review
• Most acids fall into one of 3 categories:
– Binary Acids: a H and an element from Group 6A
or 7A ( a the oxygen group or a halogen)
– Oxy Acids: contains H , O and some other element
– Carboxylic Acids: organic acids (they contain
Carbon).
Naming acids
(a review)
Binary acids- acids that are made of only two
elements (no Oxygen)
– A. Prefix is always hydro
– B. Name the second element with the suffix- ic
•
•
EX: HCl
H2S
Hydrochloric acid
Ternary acids- those acids that are made of more than
two elements; usually contain a polyatomic ion (have
Oxygen)
These can be oxy acids and carboxylic acids
– A. For the acid containing the most common polyatomic
ion of its group simply use the first part of the polyatomic
name and follow with the suffix ic.
– B. polyatomic with one less oxygen than the ic, use the
suffix ous.
– C. polyatomic with two less oxygen than the ic, use the
prefix hypo and the suffix ous.
– D. polyatomic with one more oxygen than the ic, use the
prefix per and the suffix ic.
Examples of Acid Naming Rules
• Rule 1: acids with `ic' suffix represent natural `ate'
polyatomic ions
HBrO3 bromic acid
HClO3 chloric acid
• Rule 2: when an extra oxygen is added, add a `per'
prefix to name
HBrO4 perbromic acid
HClO4 perchloric acid
• Rule 3: when 1 oxygen is taken away (from `ate' ion to ‘ite’
ion),
change the `ic' suffix to `ous'
HBrO2 bromous acid
HClO2 chlorous acid
• Rule 4: when 2 oxygens are taken away, change the `ic'
suffix to `ous' and add a `hypo' prefix
HBrO hypobromous acid
HClO hypochlorous acid
Common Industrial Acids
• Sulfuric Acid: Most commonly
produced acid (47 million tons / year). Used
is oil refineries, metallurgy and to
manufacture fertilizers, metals, paper,
paint, dyes, detergents, sugar, etc. IT is
the acid in car batteries.
• Nitric Acid: Volatile & unstable, it
stains proteins yellow , has a suffocating
odor and causes serious burns. Used to
make explosives, rubber, plastics, dyes
and pharmaceuticals.
• Phosphoric Acid: Used to
manufacture fertilizers, animal
feed, detergents & ceramics.
Diluted it’s sour and used in sodas
and for cleaning.
• Hydrochloric Acid: Produced in
the stomach for digestion, it is also
used for cleaning, food production,
activation of oil wells. Dilute- called
muriatic acid.
• Acetic Acid: Concentrated- called
glacial acetic acid.
Arrhenius Acids & Bases
• Swedish Chemist, Svante
Arrhenius, defined acids and
bases in 1884.
• Acid- substance that dissociates
in water to produce hydrogen
ions (H+)
• Base- substance that dissociates
in water to produce hydroxide
ions (OH-)
Common Arrhenius Acids & Bases
Acid
Hydrochloric acid
Formula
Base
Formula
HCl
Sodium hydroxide
NaOH
Nitric acid
HNO3
Acetic acid
HC2H3O2
Sulfuric acid
Potassium
hydroxide
KOH
Magnesium
hydroxide
Mg(OH)2
H2SO4
Calcium hydroxide
Ca(OH)2
Carbonic acid
H2CO3
Barium hydroxide
Ba(OH)2
Phosphoric acid
H3PO4
The Hydronium Ion
• Because H+ will combine with water… a
Hydronium ion is actually created.
• Water acts as an acid and a base… substances
that do so are called amphoteric.
Strong & Weak Acids
• Strong acids disassociate 100%.
Ex. HCl
– HCl + H2O → H3O+ + Cl 100%
– Excellent conductors
• Weak Acids only disassociate a small amount.
Ex. HC2H3O2
– HC2H3O2 + H2O ↔ H3O+ + C2H3O2 - 0.4%
– Poor conductors
Strong & Weak Bases
• Strong bases: Disassociates 100% . This is
called an alkaline soln. They have the strongest
affinity for H+ meaning they react 100% with water.
Ex. CaO
– O2- + H2O → 2OH• Weak bases: only partially disassociate /react
with water.
Ex. CO32– CO32- + H2O ↔ HCO3- + OH-
15.2 Acid-Base Theories
• The Arrhenius definition of acids and bases
are good, but it doesn’t describe all chemicals
that are acids and bases. Remember
Arrhenius said that they have to be in solution
with H2O. Some chemicals will act as an acid
or a base in solution with something other
than H2O.
The Brønsted-Lowry Definition
In 1923, two chemists independently
developed a new definition of acids and
bases. Danish Chemist , Johannes
Brønsted and English Chemist, Thomas
Martin Lowry said:
•An acid is any substance that can donate
H+ ions
•A base is any substance that can accept
H+ ions
Brønsted-Lowry expands the definition of
Arrhenius acids/bases.
1. Defines acids/bases independently of how
they behave in water.
2. Focuses only on the H+ ions and ignores the
OH- ions.
• Monoprotic acid- an acid that only donates
ONE proton (H+) per molecule.
Ex: HCl
• Polyprotic acids- an acid that can donate
MORE than one proton per molecule.
Ex: H3PO4
Lewis Acids & Bases
• In 1923, G.N. Lewis defined an acid and a base by
the donation of electron pairs.
• Lewis acid- an atom, ion or molecule that ACCEPTS
an ELECTRON PAIR to form a covalent bond.
• Lewis base- an atom, ion or molecule that
DONATES an ELECTRON PAIR to form a covalent
bond.
• Lewis acid-base reaction- the formation of 1 or
more bonds between and electron-pair donor &
an electron-pair acceptor.
15.3 Conjugate Acid-Base Pairs
• Conjugate means… joined together or coupled.
• An acid and a base which differ by a proton are said to
form a conjugate acid base pair or the pairs of
substances which can be formed from one another by
the gain or loss of protons are known as conjugate acid
base pairs.
Strength of Conjugate Acid-Base Pairs
The stronger the acid the weaker the conjugate base and vice versa.
Acid-Base Properties of Salts
• When salts disassociate in water, they break
down into cations and anions.
– NaCl + H2O → Na+ + Cl -
• Many of these ions are weak Brønsted-Lowry
acids or bases.
• Salt hydrolysis reactions- rxn of ions from salts
to form H30+ or OH-
• We can predict if the salt soln. will be acidic
(formed H30+ ) or basic (formed OH-)
• Salts of:
– STRONG acids + STRONG bases = neutral soln.
– STRONG acids + weak bases = acidic soln.
• formed H30+
– Weak acids + STRONG bases = basic soln.
• formed OH-
– Weak acids + weak bases = neutral soln.
16.1 The Self-ionization of Water
and pH
• Pure water does not have H2O molecules only. It
also contains H3O+ ions and OH- ions.
• Water is amphoteric, can act as an acid or a base with other
chemicals.
• Self-ionization-
Mathematical Definition
• “In pure water at 25°C, both H3O+ and OH- ions
are found at concentrations of 1.0 X 10-7 M.”
Kw= [H3O+] [OH-]
• Kw= 1.0 X 10-14
– [H3O+] = 1.0 X 10-7
– [OH-] = 1.0 X 10-7
• [H3O+] > 1.0 X 10-7> [OH-] Acidic Soln
• both = 1.0 X 10-7
Neutral soln
• [OH-] > 1.0 X 10-7> [H3O+] Basic Soln
Practice Problems
• If the concentration of H3O+ in blood is 4.0x10-8
M, the blood is acidic, basic or neutral?
– What is the concentration of OH- ions?
• What is the concentration of OH- ions in chocolate
milk if [H3O+ ] = 4.5x10-7 M?
– Is it acidic, basic, or neutral?
• What is the concentration of H3O+ ions in black
coffee if [OH-] = 1.3x10-9 M.
– Is it acidic, basic, or neutral?
The pH Scale
• In 1909, Søren Sørensen
developed the pH scale.
– 0-6.9: acid
– 7.1-14: base
• Its based on logarithms:
• pH= -log [H3O+]
• Using a calculator, try:
• -log(8.7 x 10-4)
• What is the pH of a soln with
[H3O+] = 7.3x10-5 M?
[H3O+] = 6.23x10-4 M?
[OH-] = 5.0x10-2 M? (14=pH + pOH)
Measuring pH
• 2 Common methods
1. Use an indicator, (litmus paper) – can use a
combination of indicators to get a more precise
pH reading
2. Use an pH meter.
Some Acid-Base Indicators