1. Ionic Equilibria I: Acids and Bases
Unit 8
Ionic Equilibria I: Acids and Bases

2. Chapter Goals
Identify strong electrolytes and calculate concentrations of their ions
Understand the autoionization of water
Understand the pH and pOH scales
Perform calculations involving pH, pOH, kw.

3. A Review of Strong Electrolytes
RECALL:-
Weak acids and bases ionize or dissociate partially, much less than 100%.
In this chapter we will see that it is often less than 10%!
Strong electrolytes ionize or dissociate completely.
Strong electrolytes approach 100% dissociation in aqueous solutions.

4. A Review of Strong Electrolytes
There are three classes of strong electrolytes.
Strong Water Soluble Acids
Remember the list of strong acids from Chapter 4.

5. A Review of Strong Electrolytes

6. A Review of Strong Electrolytes
Strong Water Soluble Bases
The entire list of these bases was also introduced in Chapter 4.

7. A Review of Strong Electrolytes
Most Water Soluble Salts
The solubility guidelines from Chapter 4 will help you remember these salts.

8. A Review of Strong Electrolytes
The calculation of ion concentrations in solutions of strong electrolytes is easy.
Example 18-1: Calculate the concentrations of ions in M nitric acid, HNO3.

9. A Review of Strong Electrolytes
Example 18-2: Calculate the concentrations of ions in M strontium hydroxide, Sr(OH)2, solution.
You do it!

10. The Autoionization of Water
Pure water ionizes very slightly.
The concentration of the ionized water is less than one-millionth molar at room temperature.

11. The Autoionization of Water
We can write the autoionization of water as a dissociation reaction similar to those previously done in this chapter.
Because the activity of pure water is 1, the equilibrium constant for this reaction is:

12. The Autoionization of Water
Experimental measurements have determined that the concentration of each ion is 1.0 x 10-7 M at 25oC.
Note that this is at 25oC, not every temperature!
We can determine the value of Kc from this information.

13. The Autoionization of Water
This particular equilibrium constant is called the ion-product for water and given the symbol Kw.
Kw is one of the recurring expressions for the remainder of this chapter and Chapters 19 and 20.

14. The Autoionization of Water
Example 18-3: Calculate the concentrations of H3O+ and OH- in M HCl.

15. The pH and pOH scales
A convenient way to express the acidity and basicity of a solution is the pH and pOH scales.
The pH of an aqueous solution is defined as:

16. The pH and pOH scales
In general, a lower case p before a symbol is read as the ‘negative logarithm of’ the symbol.
Thus we can write the following notations.

17. The pH and pOH scales
If either the [H3O+] or [OH-] is known, the pH and pOH can be calculated.
Example 18-4: Calculate the pH of a solution in which the [H3O+] =0.030 M.

18. The pH and pOH scales
Example 18-5: The pH of a solution is What is the concentration of H3O+?
You do it!

19. The pH and pOH scales
A convenient relationship between pH and pOH may be derived for all dilute aqueous solutions at 250C.
Taking the logarithm of both sides of this equation gives:

20. The pH and pOH scales
Multiplying both sides of this equation by -1 gives:
Which can be rearranged to this form:

21. The pH and pOH scales Remember these two expressions!!
They are key to the next three chapters!

22. The pH and pOH scales The usual range for the pH scale is 0 to 14.
And for pOH the scale is also 0 to 14 but inverted from pH.
pH = 0 has a pOH = 14 and pH = 14 has a pOH = 0.

23. The pH and pOH scales
Example 18-6: Calculate the [H3O+], pH, [OH-], and pOH for a M HNO3 solution.
Is HNO3 a weak or strong acid?
What is the [H3O+] ?

24. The pH and pOH scales
Example 18-6: Calculate the [H3O+], pH, [OH-], and pOH for a M HNO3 solution.

25. The pH and pOH scales
To help develop familiarity with the pH and pOH scale we can look at a series of solutions in which [H3O+] varies between 1.0 M and 1.0 x M.
[H3O+]
[OH-] pH
pOH
1.0 M
1.0 x M
0.00
14.00
1.0 x 10-3 M
1.0 x M
3.00
11.00
1.0 x 10-7 M
7.00
2.0 x M
5.0 x 10-3 M
11.70
2.30