http://www.ck12.org Chapter 21. Acids and Bases
21.3 Acid and Base Strength
Lesson Objectives
- Explain the difference between a strong acid or base and a weak acid or base.
- Write equilibrium expressions for the ionizations of weak acids and weak bases. Explain how the value of Ka
or Kbrelates to the strength of the acid or base. - Calculate an unknown Kaor Kbfrom the solution concentration and the pH.
- Calculate the expected pH of a solution containing a given concentration of a weak acid or base that has a
known Kaor Kbvalue.
Lesson Vocabulary
- acid ionization constant
- base ionization constant
- strong acid
- strong base
- weak acid
- weak base
Check Your Understanding
Recalling Prior Knowledge
- What is meant by the ionization (or dissociation) of a polar or ionic compound that is dissolved in water?
- How is the pH of a solution containing a strong acid or strong base determined?
Some acids, such as sulfuric acid and nitric acid, are strong acids. Working with strong acids requires special care
and protective clothing and eyewear. Other acids, such as acetic acid and citric acid, are encountered in many foods
and beverages. These weak acids are considerably less dangerous. In this lesson, you will learn about the differences
between strong and weak acids and bases.
Strong and Weak Acids and Bases
Acids are classified as either strong or weak, based on the extent to which they ionize in water. Astrong acidis an
acid which is completely ionized in aqueous solution. As we saw earlier, hydrogen chloride (HCl) is a gas as a pure
compound, but it ionizes into hydrogen ions and chloride ions upon being dissolved into water.
HCl(g)→H+(aq)+Cl−(aq)