# Aqueous Solutions and ph by wuxiangyu

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```									Aqueous Solutions and pH
Hydronium Ions and Hydroxide Ions

   Acids produce the hydronium (H3O+) ion in water:
HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)

   Bases produce the hydroxide ion (OH-) in water:
NaOH(aq)  Na+(aq) + OH-(aq)
Self-Ionization of Water

   Water produces both hydronium and hydroxide ions through self-
ionization:
H2O(l) + H2O(l)  H3O+(aq) + OH-(aq)
(Brackets [ … ] are used to symbolize concentration in molarity)

Kw = ionization constant of water

Kw = [H3O+] [OH-]
(Kw = 1 x 10-14 M2)
[H3O+] = 1 x 10-7M               [OH-] = 1 x 10-7M
pH Scale
- A means of expressing acidity or basicity of a solution.

http://www.mpcfaculty.net/mark_bishop/pH_range.jpg
pH

   Expressing acidity or basicity in terms of H3O+ or OH-
concentration can be difficult due to extremely small
values.
   pH is a more convenient means of quantitatively
describing acidity of a solution.
   pH stands for “pouvoir hydrogene” – power of
hydrogen.
pH Calculations

pH = -log[H3O+]

The logarithm (log) of a number is equal to the power
that 10 must be raised to equal the number.

Example:      log (1 x 10-7) = -7
pH Practice

1) What is the pH of a solution with a [H3O+] = 1.0 x 10-7?
pH = -log(1 x 10-7)
pH = -(-7.0)
= 7.0
2) What is the pH of a solution with a [H3O+] = 3.21 x 10-4?

pH = -log (3.21 x 10-4)
pH = - (-3.49)
= 3.49
pOH Calculations & Practice

pOH = -log[OH-]
1) What is the pOH of a solution with a [OH-] = 1.0 x 10-9?
pOH = -log(1 x 10-9)
pOH = -(-9.0)
= 9.0
2) What is the pOH of a solution with a [OH-] = 6.74 x 10-8?
pOH = -log (6.74 x 10-8)
pOH = - (-7.17)
= 7.17
Calculating Concentrations from pH & pOH

[H3O+] = 10-pH              [OH-] = 10-pOH

1) What is the [H3O+] of a solution with a pH = 12.3?
[H3O+] = 10-12.3
[H3O+] = 5.01x10-13M
2) What is the [OH-] of a solution with a pOH = 4.25?
[OH-] = 10-4.25
[OH-] = 5.62x10-5M
Connection between hydronium & hydroxide

pH + pOH = 14

[H3O+] [OH-] = 1 x 10-14

Neutral solutions:
[H3O+] = [OH-] & pH = 7
Acidic solutions:
[H3O+] > [OH-] & pH < 7
Basic solutions:
[H3O+] < [OH-] & pH > 7
Summary of Equations

pH = -log[H3O+]
pOH = -log[OH-]

[H3O+] = 10-pH
[OH-] = 10-pOH

pH + pOH = 14
[H3O+] [OH-] = 1 x 10-14
Practice Chart

[H3O+]       [OH-]       pH     pOH

6.7 x 10-4

3.17

12.2

2.5 x 10-8
Calculator Help

If you have a TI-30Xa such as the one
shown, you must enter the information in
the formula backwards.
For example:
What is the pH of a solution with a [H3O+] = 3.21 x 10-4?
3   2           1

pH = - log (3.21 x 10-4)

1) Enter 3.21EE-4
2) Press “log”
3) Press +/- key
Calculator Help cont.

What is the [H3O+] of a solution with a pH = 12.3?
3   2 1

[H3O+] = 10 -12.3

1) Enter 12.3
2) Press +/- key
3) Press 10x key
Graphing and 2-line calculators