8.1 / 18.1 THEORIES OF ACIDS AND BASES
INTRODUCTION:
Common Acids and Bases In the Home:
Product
Acid(s) Contained In the
Product
Citrus fruits (e.g.
lemons, limes,
oranges, tomatoes)
Dairy Products
Citric acid and ascorbic
acid(Vitamin C)
Vinegar
Ethanoic acid (aka acetic
acid)
Carbonic acid, phosphoric
acid, citric acid
3-methyl-2-hexanoic acid
Soft drinks
Underarm odour
Product
ACIDS
pH
pOH
[H+] x [OH-]
Effect on
Red
Litmus
Effect on
Blue
Litmus
BASES
pH
pOH
[H+] x [OH-]
Effect on
Red
Litmus
Effect on
Blue
Litmus
Lactic acid
Base Contained In the
Product
Oven/drain cleaner
Sodium hydroxide
Baking soda
Sodium hydrogen carbonate
Washing soda
Sodium carbonate
Glass cleaner
ammonia
*In a __________________ solution the [H+] = [OH-] and pH =7.00 (at ______°C)
*In a __________________ solution the [H+] > [OH-]
*In a __________________ solution the [H+] < [OH-]
*There are ______ ACID-BASE THEORIES which you should know by name and definition. These theories do not
contradict each other but are inclusive of each other.
THEORY #1: THE ARRHENIUS THEORY OF ACIDS AND BASES (1887)
 simplest and oldest of all the acid/ base theories
a) ARRHENIUS ACID - a substance that dissociates in water to produce one or more _____________ ions (H+)
Examples:
b) ARRHENIUS BASE - a substance that dissociates in water to form one or more ______________ ions (OH-)
Examples:
THEORY #2: THE BRONSTED-LOWRY THEORY OF ACIDS AND BASES (1923)
 developed in response to the limitations/problems associated with the Arrhenius theory
PROBLEM 1:
*Hydrogen ions (i.e. protons) do not actually exist in isolation in aqueous solution – this was not
discovered until the early 1900’s. The bare proton (hydrogen ion) bonds with one of the unshared
pairs of electrons on a water molecule; that is, it forms a _____________covalent bond with water.
The resulting ion is call a __________________ ion.
PROBLEM 2:
*Several substances, that do not contain ___________________, produce basic solutions when dissolved in water.
Example 1:
NH3(aq)
+
H2O(l)
*Conjugate acid-base pair #1 =_______/_______
*Conjugate acid-base pair #2 =_______/_______
*In most acid-base interactions, a ___________ (H+ ion) is
transferred from one reactant to another – this idea is the basis of the
Bronsted-Lowry theory.
IMPORTANT DEFINITIONS:
BRONSTED-LOWRY ACID - a substance which
_______________ a proton in water solution
BRONSTED-LOWRY BASE: a substance which will
_______________ a proton in water solution.
CONJUGATE BASE – the entity that remains after the _________________ donates its ___________
CONJUGATE ACID - the entity that exists after the _____________accepts a proton
*REMEMBER:
- CONJUGATES are ALWAYS __________________ and the ACIDS/BASES are ALWAYS_________________!
- The entities in each conjugate acid-base pair differ by one ________________ only!
- Pneumonic = “BAAD” – Bases Accept, Acids Donate
Example 2:
HF(aq)
+
H2O(l)
*Conjugate acid-base pair #1 =_______/_______
*Conjugate acid-base pair #2 =_______/_______
*Extension(NH3 as a cleaner)  http://www.nbclearn.com/portal/site/learn/chemistry-now/molecule-profiles
*The _____________ arrows used in examples 1 &2 are used to represent reactions that do not go to completion –
reactions in which dynamic equilibriums are established. Both ammonia and hydrofluoric acid ionize partially. When
an acid ionizes partially(usually less than 1%) we say it is a ________________ acid. In contrast, ____________ acids
ionize _____________________. When a base ionizes partially we say it is a _______________ base. If it ionizes
completely it is a _________________ base. More on weak and strong acids and bases later.
*Also, notice from the above examples that H2O is __________________; that is, it may _______________ (act as a
base) OR _______________ (act as an acid) a proton depending on the chemical reaction. Water can also be
described using the term amphiprotic – an entity that can both donate or receive a proton. *All B-L acids and bases
are both amphoteric and amphiprotic.
PRACTICE: Represent the amphoteric/amphiprotic nature of the hydrogen carbonate ion (HCO3 -, the anion in
baking soda ) using two separate equations.
HCO3- acting as an ACID:
HCO3- acting as an BASE:
PRACTICE with BRONSTED-LOWRY TERMS:
1.
a) What is the conjugate acid of ammonia? NH3 + H2O  NH4 + + OH-1
b) What is the conjugate acid of NH ?
c) What is the conjugate acid of sulfate ion?
d) What is the conjugate acid of water?
A.____________
A.____________
A.____________
A.____________
2.
a) What is the conjugate base of ammonia?
-1
b) What is the conjugate base of NH2 ?
c) What is the conjugate base of hydrogen sulfate ion?
d) What is the conjugate base of water ?
e) What is the conjugate base of sulfuric acid?
A.____________
A.____________
A.____________
A.____________
A.____________
3.
a) If water is the conjugate acid, what is the base?
b) If ammonia is the conjugate base, what was the acid?
c) If bisulfate ion, HSO4-, is the conjugate acid, what was the base?
d) If bisulfate ion is the conjugate base, what was the acid?
e) What is the conjugate acid of cyanide ion?
f) What is the conjugate base of bicarbonate ion?
g) What is the conjugate acid of bicarbonate ion?
h) If the bisulfite ion, HSO3-, is the conjugate acid, what was the base?
i) If ammonium ion is the conjugate acid, what was the base?
A.____________
A.____________
A.____________
A.____________
A.____________
A.____________
A.____________
A.____________
A.____________
2
4. Identify the two conjugate acid-base pairs in each of the following:
a)
HCO3-(aq) + S2-(aq)
b)
H2CO3(aq) + OH-(aq)
c)
HSO4-(aq) + HPO42-(aq)
HS-(aq) + CO32-(aq)
HCO3-(aq) + H2O(l)
H2PO4-(aq) + SO42-(aq)
*d) H2O(l) + H2O(l)
H3O+(aq) + OH-(aq)
*Remember this rxn for later: i.e. the AUTOIONIZATION of WATER.
5. Identify all the amphoteric entities in question 4.
6. Some ions can form more than one conjugate acid-base pair. List the two conjugate acid-base pairs involving the
hydrogen carbonate ion in the reactions in question 4.
18.1 THEORY #3: THE LEWIS THEORY OF ACIDS AND BASES (Early 1920’s)
 Not unlike the Arrhenius theory, the Bronsted-Lowry theory contains limitations also.
 The Lewis theory is actually an extension of the B-L theory.
 Lewis defined an acid as a species that accepts a pair of _________________ to form a ______________ bond.
Therefore, according to Lewis’ definition, all reactions involving the formation of a dative bond are acid-base
reactions.
LEWIS ACID - a substance which can __________________ an __________________ PAIR around its central atom
LEWIS BASE - a substance which can _______________ an _________________ PAIR from its central atom
 B-L acids and bases are all acids and bases in the Lewis model, but the reverse is not always true! *The term
“Lewis acid” is usually reserved for a species that is NOT ALSO A BRONSTED-LOWRY ACID.
EXAMPLES:
i) boron trifluoride + ammonia:
ii) ferric ion(Fe3+) + any ligand(e.g. H2O):
*iii) aminomethane + water:
*Note how example (iii) also represents a Bronsted-Lowry acid-base interaction.
*What is the difference between the terms amphoteric and amphiprotic?
*HINTS:
 GROUP 3, electron deficient compounds such as _________ and ________ are Lewis ______________.
However, any species that can accept an electron pair into its valence shell (e.g. CH3+) is capable of acting as a Lewis
acid.
 GROUP 5 compounds (with a lone pair), such as__________ and _________ are Lewis ______________.
 __________________ metal ions are Lewis ______________ and the ________________around them are Lewis
_______________.
 *Nucleophiles are Lewis ___________. (*More on this when we get to organic chem.)
Extension:
a) Cisplatin(Lewis acid) = anti-cancer drug…stops cell replication via Lewis acid-base interaction with
nitrogen(Lewis base) component of DNA
b) Iron(Fe2+) in a hemoglobin molecule  oxygen(the Lewis base/Ligand) “hitches a ride” with iron ion(Lewis acid)
on a hemoglobin molecule via Lewis acid-base interaction.
SUMMARY: ACID-BASE THEORIES
Theory
ACID Definition
1) Arrhenius
Produces ______ in water
BASE Definition
Produces ______in water
*2) Bronsted-Lowry
H+(aq) _________________
H+(aq) ___________________
*3) Lewis
Electron pair ________________
Electron pair _______________
*In IB chemistry, theories 2 & 3 are the primary focus.