21.5. Salt Solutions http://www.ck12.org
21.5 Salt Solutions
Lesson Objectives
- Describe salt solutions as acidic, basic, or neutral.
- Calculate the pH of a salt solution when given relevant data.
- Explain how buffers work to maintain pH.
Lesson Vocabulary
- conjugate base: The deprotonated form (A−) from a given acid acid (HA).
- conjugate acid: The resulting molecule after the base accepts a proton.
- buffer: Solutions which resist small changes in pH when an acid or a base is added to the system.
- pKa: The negative logarithm of the Ka; a lower pKaindicates a more acidic compound.
Check Your Understanding
- How do you calculate the concentrations of various reaction components at equilibrium?
Introduction
Neutralization reactions between an acid and a base yield a salt and water. In some cases, this results in a completely
neutral solution. However, some salts are weakly acidic or basic. How can we tell whether a given salt will act as
an acid or base? Looking at the relative strengths of the acid and base that were used to form the salt can give us
information on the acid-base properties of the resulting solution.
Salts and Their Interactions with Water
Salts Forming Neutral Solutions
The simplest situation is a salt formed by combining a strong acid and a strong base. These salts are neither acidic
nor basic, so they do not affect the pH of the solution when dissolved in water. For example, the ionic compound
NaNO 3 could be prepared by combining the strong acid HNO 3 and the strong base NaOH. If we were to dissolve
NaNO 3 in water, it would dissociate into Na+and NO 3 −ions. Neither ion is a strong enough acid or base to cause
any noticeable proton transfers, so the pH of the pure water is not altered.