Pg 569 - 581

Amphoteric substance: can act as an acid or as a base◦ Water is the most common amphoteric substance

Self-ionization of water:

H2O(l) + H2O(l) H3O+(aq) + OH-(aq)

At 25oC actual concentrations are:◦ [H3O+] = [OH-] = 1.0 x 10-7 M

The product of the two concentrations is:◦ [H3O+]*[OH-] = 1.0 x 10-14 @ 25oC

We call this Kw

To simplify the equation, we write H3O+ as H+

Kw = [H+]*[OH-] = 1.0 x 10-14 @ 25oC

Kw = ion-proton constant◦ In any aqueous solution at 25oC, no matter what it

contains, the product of [H+] and [OH-] must ALWAYS equal 1.0 x 10-14

What will happen if the concentration of H+ increases? If it decreases?◦ If [H+] increases, [OH-] decreases◦ If [H+] decreases, [OH-] increases

1. [H+] = [OH-] neutral2. [H+] > [OH-] acidic3. [H+] < [OH-] basicRemember: [H+]*[OH-] = 1 x 10-14

Calculate [H+] or [OH-] as required for each of the following solutions at 25 °C, and state whether the solution is neutral, acidic, or basic.

a) 1.0 x 10-5 M OH-

b) 1.0 x 10-7 M OH-

c) 10.0 M H+

H+ = 1.0 x 10-9 M, basic

H+ = 1.0 x 10-7 M, neutral

OH- = 1.0 x 10-15 M, acidic

Calculate [H+] in a solution in which [OH-] = 2.0 x 10-2 M. Is this solution acidic, neutral or basic?

5.0 x 10-13 M, basic

pH measures the “power” of the hydrogen ion◦ “Power” refers to exponent of 10◦ Based on the base 10 log scale.

pH = -log[H+] If [H+]= 1.00 x 10-7, pH = ? If [H+]= 1.00 x 10-2, pH = ?

[H+] = inverse log (-pH) If pH = 9, [H+]=?

If a solution has a pH of 2, how much more acidic is it than a solution with a pH of 4? 100 times more acidic!!

Try the following:1. Find pH if [H+] = 3.5 x 10-3

Find pH if [OH-] = 1.4 x 10-3

2. If the pH = 9.4 what is [H+] ?If the pH = 4.9 what is [OH-] ?

Answers: 1) 2.45 2) 11.15 3) 4.0 x 10-10 4) 7.9 x 10-10

pOH = -log[OH-] If pH = 5, What would pOH be?

pH + pOH = 14.00

1. The pOH of a solution is 5.67. What is the [OH-] of the solution? What is the [H+]?

2. The [OH-] of drain cleaner is 3.2 x 10-11M. What is the pOH? The pH? Is it acidic, basic or neutral?

1) 2.1 x 10-6M and 4.8 x 10-9M

2) 10.50 and 3.50 = acidic!!