Chemistry 122
Classification of Acids and Bases
Name ________________________
Hydronium
1. What is the chemical formula for the hydronium ion?
2. Explain how the hydronium ion is formed.
3. a) Write an equation to show HCO3- reacting with water to produce hydronium ions and another product.
b) Write an equation to show HSO4- reacting with water to produce hydroxide ions and another product.
The Bronsted-Lowry Definition
4. Over time, chemists have discovered that reactions of acids and bases do not always have to involve
______________________.
5. Describe how Bronsted-Lowry define acids and bases.
6. Identify whether each reactant, in the following reactions, are an acid or a base. Just write “A” or “B”
above the chemicals formula.
a)
HF + SO3-2   F- + HSO3-
b) CO3-2 + CH3COOH   CH3COO- + HCO3 –
c)
HCO3 - + HSO4-   SO4-2 + H2CO3
7. Define “amphiprotic”.
8. How will you use your acid-base table to determine which substances are amphiprotic?
9. Explain how you know the H2PO4 - ion is amphiprotic just by looking at its formula.
Conjugate Pairs
10. How many acids and bases will there be in an equilibrium reaction between an acid and a base?
11. Go back to question # 6 and indicate the acid and base for the reverse reaction.
12. Define a “conjugate pair”.
13. Go back to question # 6 and draw a dotted line to connect the conjugate pairs in each reaction.
14. How could you identify conjugate pairs using only your acid-base table?
15. If an acid is considered quite strong, what is the strength of its conjugate base?
The Hydronium Ion
In this unit, we will discuss the hydronium ion (H3O+). When an acid dissolves in water it
produces a hydrogen ion (H+) and a negative ion.
HCl

H+ + Cl-
A hydrogen ion is really just one positively charged proton so it will easily be attracted to
negative charges. A water molecule has an overall neutral charge, however, due to its shape
there is a positively charged end and a negatively charged end (polar).
H+
H+
positive end
overall neutral
O
-2
negative end
The hydronium ion is formed when the hydrogen ion is attracted to (not fully bonded) the
negative end of the water molecule.
H+
H+
O -2
H+
We can show this occurrence in an equation.
HCl + H2O 
H3O+ + Cl-
If water loses one of its hydrogen ions during a reaction it will produce hydroxide ions.
We can also show this occurrence in an equation.
HPO4-2 + H2O

H2PO- + OH-
The Bronsted-Lowry Definition
Arrhenius could only predict whether a substance is an acid or base if the substance was
dissolved in water and observed the ions produced. Due to modern knowledge, we now realize
that acid-base reactions can occur without the presence of water.
Two scientists, Bronsted and Lowry, looked at what acids and bases did during the
reaction as opposed to looking at what ions were produced in water.
Bronsted- Lowry noticed that acids donate/give off a hydrogen ion and bases will
accept/gain a hydrogen ion.
H+
HCl +
H2O  H3O+
Cl-
+
acid
H+
NH3 + H2O  NH4+
+ OH-
base
H+
H3O+ + NH3  H2O +
acid
NH4+
base
Some compounds/ions are amphiprotic. This means that the same compound/ion can be
an acid in one reaction and a base in a different reaction.
H+
HSO4- + CO3-2   SO4-2
+
HCO3-
acid
H+
HSO4- + H3O+

H2SO4
+
H2O
base
Since acids are hydrogen ion donors, a compound/ion must have at least one hydrogen
ion to be an acid. Also, since bases are hydrogen ion acceptors, they often (not always) have a
negative charge (negative charge would attract the positive hydrogen ion).
You will be provided with an Acid-Base table that lists all possible acids (in order of
decreasing strength) and all possible bases (in order of increasing strength). You can identify an
amphiprotic substance using this table. An amphiprotic substance will be located somewhere in
the acid column and somewhere in the base column.
Conjugate Pairs
For reactions that are reversible, there will be an acid and base for the forward reaction
and an acid and base for the reverse reaction.
Forward reaction
Reverse reaction
+
H+
H
HCN + CO3-2
acid

HCO3- +
base
CN-
acid
base
Every acid will have a conjugate base and every base will have a conjugate acid.
As an acid donates a H+ it forms its conjugate base. They are known as a conjugate pair.
As a base accepts a H+ it forms its conjugate acid. They are known as a conjugate pair.
So….the chemical formulas of the conjugate pair will differ by one H+.
Conjugate Pair
HCN + CO3-2
acid
base

HCO3conjugate acid
+
CNconjugate base
Conjugate Pair
You will notice on your Acid-Base Table that conjugate pairs are located directly across
from one another. As well, since the strength of the acids decrease down the table but the
strengths of the bases increase down the table, the strengths of the two substances that make up
a conjugate pair often have an opposite relationship. EX: If one is strong the other is weak.
(except for the middle of the table …. both have medium strength).