http://www.ck12.org Chapter 21. Acids and Bases
FIGURE 21.7
The flowchart shows the way to convert
between hydrogen ion concentration, hy-
droxide ion concentration, pH, and pOH.Lesson Summary
- Water self-ionizes into hydrogen ions and hydroxide ions. The equilibrium constant for this process is referred
to as Kwand is equal to 1.0× 10 −^14 at 25°C. - The concentrations of H+and OH−are both equal to 1.0× 10 −^7 M in pure water. If the H+concentration
is higher than the OH−concentration, the solution is acidic. If the OH−concentration is higher than the H+
concentration, the solution is basic. - The pH of a solution is the negative logarithm of the H+ion concentration. Pure water or a neutral solution
has a pH of 7.0. Acidic solutions have pH values that are lower than 7, while basic solutions have pH values
that are greater than 7. - The H+ion concentration can be calculated when the pH is known by using the antilog function.
- The pOH scale is based on the concentration of the OH−ion.
Lesson Review Questions
Reviewing Concepts
- Describe the process by which water self-ionizes, and explain why pure water is considered to be neutral.
- Explain why the concentrations of the hydrogen ion and the hydroxide ion cannot both be greater than 1×
10 −^7 M in an aqueous solution. - Indicate whether solutions with the following pH values are acidic, basic, or neutral.
a. pH = 9.4
b. pH = 7.0
c. pH = 5.0