1. Self-ionization of Water and pH
Objectives:
1. Identify the ions present in pure water and give their concentrations.
2. Define pH and explain how the pH scale is used.
3. Identify what a buffer is and how the strength of it is related to the buffer capacity.

2. Arrhenius Definition
An acid is a substance that releases (dissociates) Hydrogen ions (H+) in water
monoprotic - releases 1 H+ ion (HCl)
diprotic - releases 2 H+ ion (H2SO4)
triprotic - releases 3 H+ ion (H3PO4)
An base is a substance that releases (dissociates) Hydroxide ions (OH-) in water
ex: KOH, NaOH, Ca(OH)2, Mg(OH)2

3. Bronsted-Lowry Definition
An acid is a proton (H+) donor
A base is a proton acceptor
conjugate acid-base pairs are substances related by the loss or gain of a H+ ion
strong acids have a weak conjugate base
weak acids have a strong conjugate base
Conjugate base/acid pair
Conjugate acid/base pair

4. Lewis Acid Definition
Lewis Acid and Bases An acid is an electron pair acceptor
A base is an electron pair donor
H+ + OH- g H2O
In this reaction the H+ ion accepts the electron pair donated by the OH- ion to form H2O

5. Self ionization
Water has many unusual properties. One of these properties is water's ability to act as either an acid or a base (H2ODH3O++ OH-)
Amphoteric is the name given to a substance that can act as either an acid or a base.
Water becomes hydronium and hydroxide ions through self ionization
The concentrations of each for pure water are equal at a pH of 7

6. Ion-Product
The ion-product (Kw) can be used to find the concentration of acid and base in any solution based on the following assumptions:
The formula for Kw for ALL solutions at 25oC is Kw = [H3O+][OH-] = 1x10-14
pH of pure water is 7, so the concentration of H3O+ is 1 x10-7
The concentration of base therefore is [OH-] = 1x10-14/1x 10-7 = 1 x10-7
EX: If a solution has 1 x10-2 H3O+ions, what is the concentration of the base ions?
[OH-] = 1x10-14/1x 10-2 = 1 x10-12

7. pH Scale
The pH scale was developed to help people interpret the amount of hydronium ions compared to the amount of base in a solution. The scale was developed by Soren Sorenson, a Danish biochemist, and is based on the -log of the hydronium ion (H3O+) concentration in solution.{-log[H3O+]}.
The pH scale contains values between 0 and14.
Each whole number change in the pH of a substance represents a 10 fold increase in the number of hydronium ions.
Scale is from
0-7 acidic (solutions with a higher hydronium ion (H3O+)concentration than x10-7 are acidic ; 0 most acidic)
7 neutral
7-14 basic (solutions with a higher hydroxide ion (OH-)concentration than x10-7 are basic ; 14 most basic)
can be measured using a chemical indicator
a weak acid or base that changes color as the pH changes (gain or lose H+ ions)

8. pH Scale
pH scale can be used to determine the amount of hydronium and hydroxide concentrations in solution with the equation pH + pOH = 14 and the ion product (Kw). Consider the following examples.
example: A solution with 1 x 10-2 H3O+ ions, what is the pH and pOH of the solution?
to get the pH simply change the negative exponent to a positive pH
pH = 2
pOH = =12
A solution with 1 x 10-2OH- ions
Use the ion product constant 1st to find the concentration of hydronium
Kw=1 x 10-14/1 x 10-2OH-= 1 x H3O+ ions
pH = 12
pOH = 2