BSC 1010 Fall 2010
Name:_____________________
Acids and Bases and pH
Periodic Table of
Elements
Molarity (M) = mole of solute (mol)
liters of solution (L)
Moles of solute = Mi x Vi = Mf x Vf
1. Acids and Bases
A. Properties of Acids and Bases
 An acid is a compound that releases hydrogen ions (H+) in solution:
HCl
H+ + Cl(hydrochloric acid) (hydrogen ion) (chloride ion)
BSC 1010 Fall 2010
 A base is a compound that accepts H+ ions from solution
 Bases release hydroxide ions into solution (-OH):
-OH
+ H+
H2O
-OH
NaOH
+ Na+
(sodium hydroxide)
(hydroxide ion) (sodium ion)
B. Polyprotic Acids and Bases
 A polyprotic acid is a compound that produces two or more hydrogen
ions (H+) in solution:
2H+ + SO42(2 hydrogen ions) (sulfate ion)
H2SO4
(sulfuric acid)
 A polyprotic base is a compound that accepts 2 or more hydrogen ions in
solution:
 A polyprotic base releases 2 or more hydroxide ions into solution:
Ca(OH)2
(calcium hydroxide)
2-OH + Ca2+
(2 hydroxide ions) (calcium ion)
C. Hydrogen Ions from Water
 Water molecules self-ionize and behave as both an acid and a base
 A water molecule self ionizes to produce one hydrogen (H+) ion and one
hydroxide (–OH) ion:
H2O
H+ + -OH
H+ + -OH
H2O
❖ In pure water, water molecules immediately pick up any freed hydrogen ions
(H+) forming the hydrondium ion (H3O+):
H2O + H+
H3O+
(hydronium ion)
 Because water self-ionizes, it exists in three forms: H2O, H3O+, -OH
 Most water exists in the H2O form. Water molecules self-ionize at a very
small extent.
BSC 1010 Fall 2010
 In pure water at 25oC the concentration of hydrogen ions ([H+]) and the
concentration of hydroxide ions ([-OH]) are each only 1.0x10-7M
[H+] = [OH-] = 1.0x10-7M = 0.0000007M
 The concentration of hydrogen ions ([H+]) and the concentration of hydroxide
ions ([-OH]) are equal
C. Acidic and Basic Solutions
 Any aqueous solution in which the concentrations of hydrogen ions ([H+]) and
hydroxide ions ([-OH]) are equal is considered to be a neutral solution
 An aqueous solution that contains a higher concentration of hydrogen ions
than hydroxide ions is considered to be an acid solution
 An aqueous solution that contains a higher concentration of hydroxide ions
than hydrogen ions is considered to be a basic solution (alkaline solution)
D. Calculations
 In any aqueous solution the concentrations of hydrogen ions ([H+]) and
hydroxide ions ([-OH]) are interdependent. As the concentration of one
increases, the concentration of the other must decrease proportionately

In pure water the product of the hydrogen-ion concentration and the
hydroxide-ion concentration equals 1.0x10-14M2:
[H+] = [OH-] = 1.0x10-7M
[H+] x [-OH] = 1x10-14 M2
(1x10-7 M) x (1x10-7 M) = 1x10-14 M2
❖ For any aqueous solution, the product of the hydrogen-ion
concentration and the hydroxide ion concentration must equal 1.0x10-14M2
[H+] x [-OH] = 1x10-14 M2
Practice:
1. If the [H+] in an aqueous solution is 1.0x10-5M, what is the [-OH]?
2. If the [-OH] an aqueous solution is 1.0x10-3M, what is the [H+]?
BSC 1010 Fall 2010
E. pH
pH = -log [H+]
 pH is the inverse log of the hydrogen-ion concentration. The pH scale is used
to simply the large numbers associated with concentrations.
 For example:
[H+] of H2O = 1.0x10-7M
pHH2O = -log (1.0x10-7)
pHH2O = 7
 Practice: Calculate the pH of the two preceding practice questions:
1.
2.
F. pH Scale
 The pH of neutral water is 7; therefore, 7 is neutral on the pH scale.
 Not all solutions are neutral, solutes in an aqueous solution may dissociate
releasing H+ ions or –OH ions causing the solution to become acidic or basic.
 The pH Scale is inversely proportional to [H+]:
- As [H+] increases, pH value decreases; therefore, acidic solutions have a
lower pH on the pH scale.
-As [H+] decreases, pH value increases; therefore, basic solutions have a
higher pH on the pH scale.