Chemistry – Dr. May Notes
Acids, Bases, and Salts
Properties of Acids and Bases
Acids and bases can be distinguished from each other:
Characteristic Properties of Acids and Bases
Water Solutions of Acids
Taste Sour
React with metals to give off hydrogen gas
Conduct electricity
Turn litmus paper red
Turn phenolphthalein colorless
Universal Indicator is yellow
Water Solutions of Bases
Taste bitter and feel slippery
Do not react with metals
Conduct electricity
Turn litmus paper blue
Turn phenolphthalein pink
Universal Indicator is blue
Defining Acids and Bases
Svante Arrhenius: Acids form hydronium ions in water while bases form
hydroxide ions.
Hydronium ions: [H3O+] (H+ combined with H2O)
Hydroxide ions: [OH]
Johannes Brønsted: Definition based on what happens during an acid base
reaction and is not limited to aqueous solutions.
Brønsted Definitions
Brønsted Acid
Brønsted Base
+
A substance that donates an H ion (proton) A substance that accepts an H+ ion (proton)
to another substance
from another substance
Acid and Base Strength
Acid strength depends on the number of hydronium ions formed per mole of acid.
HCl is a strong acid and acetic acid is a weak acid. The ionization of acetic acid is more
reversible the HCl ionization.
CH3COOH
Acid
+
⇋
H2O
Base
CH3COO
Conjugate
Base
1
+
H3O+
Conjugate
Acid
Acid-Base Reactions - Neutralization
An acid neutralizes a base when the two react completely, leaving no excess acid
or base.
Acids that donate more than one proton are called polyprotic acids. Under the
conditions of complete neutralization, all the protons leave the acid. Steps 1 (one mole of
base) and 2 (two moles of base) are partial while step 3 (three moles of base) is complete.
Step 1:
Step 2:
Step 3:
H3PO4 + NaOH  NaH2PO4 + H2O
H3PO4 + 2 NaOH  Na2HPO4 + 2 H2O
H3PO4 + 3 NaOH  Na3PO4 + 3 H2O
Sulfuric acid (H2SO4) and HOOCCH2C(OH)(COOH)CH2COOH (citric acid) are
other examples of polyprotic acids.
Titrations
The purpose of titration is to determine the amount of acid or base in an unknown
solution using the relationship
M (molarity) ‗ moles
liters
or
moles = M x liters
During titration, we are taking a certain number of moles of acid (for example)
and adding an equal number of moles of base (of known concentration) to it. An indicator
tells us when the number of moles is equal (phenolphthalein or universal indicator).
We know that the moles of the acid equals the moles of the base which tells us
that the molarity of the base times the volume is equal to the molarity of the acid times
the volume of the acid.
molarity(acid) x volume(acid) = molarity(base) x volume(base)
Since volume and concentration are on both sides of the equation, you can use
any units you want. We will choose milliliters for titration. For example, if we use 18.6
ml of a 0.1 M NaOH solution to neutralize 10 ml of an acid solution, we can easily
calculate the concentration of the acid as follows:
Molarity(acid) x 10 ml = 0.1 M x 18.6 ml
Molarity(acid) = 1.86
10
Molarity(acid) = 0.186 M
2
pH and Acid-Base Equilibrium - pH Scale and Indicators
pH has been defined as the negative logarithm of the hydronium ion concentration
in an aqueous solution
pH =  log [H3O+]
A logarithm of a number is the power to which 10 must be raised to equal that
number.
To determine the pH of a 0.0034 M nitric acid solution we find the negative log of
0.0034 (3.4 x 103). The log of 3.4 = 0.531 and the log of 103 is 3. The logarithm of
0.0034 is 0.532  3 =  2.468. The negative logarithm is 2.468, which is the pH of a
0.0034 M solution of nitric acid.
The pH of a 0.0034 M HNO3 solution = 2.468
Acid-Base Equilibrium: Kw and Ka
Kw = [H3O+][OH]
At 25oC Kw = [H3O+][OH] = 1.0 x 1014
Kw is the usual way that the equilibrium constant (Keq) for the ionization of water
is expressed.
For an acid like HF, the acid dissociation constant is expressed as
[H3O+] [F]
Ka =
[HF]
Ka (at 25oC) = 6.6 x 104
Buffers
A solution that resists changes in pH even when acids and bases are added is
called a buffer.
3
Common Acids and Bases
Molecular Formula
(Acids)
HCl
H2SO4
HNO3
H3PO4
H2CO3
HOH
CH3COOH
HCOOH
HOOCCOOH
HF
HBr
Molecular Formula
(Bases)
NaOH
KOH
NH4OH
CH3NH2
NH3
(CH3CH2)3N
Common Name
Other Name
Hydrochloric acid
Sulfuric acid
Nitric acid
Phosphoric acid
Carbonic acid
Water
Acetic acid
Formic acid
Oxalic acid
Hydrofluoric acid
Hydrobromic acid
Hydrogen chloride
Hydrogen sulfate
Hydrogen nitrate
Hydrogen phosphate
Hydrogen carbonate
Hydrogen hydroxide
Ethanoic acid
Methanoic acid
Ethanedioic acid
Hydrogen fluoride
Hydrogen bromide
Common name
Other name
Sodium hydroxide
Potassium hydroxide
Ammonium hydroxide
Methyl amine
Ammonia
Triethyl amine
Caustic
Lye
Ammonia water
TEA
Acid-Base Reactions form a Salt and Water
Acid
+
Base

Salt
+
Water (neutralization)
Compound + Compound  Compound + Compound (Double Replacement)

H2SO4 + Mg(OH)2
H3PO4 + 3 KOH

3 H2SO4 + 2 Al(OH)3
HNO3
2 HCl
H2SO4
+
NaOH
+
Mg(OH)2
+
MgSO4
2 KOH
K3PO4
+ 2 H2O
+ 3 H2O

Al2(SO4)3
+ 6 H2O

NaNO3
+


4
MgCl2
K2SO4
H2O
+
+
2 H2O
2 H2O