Question

Why aren't ionic compounds like \(\mathrm{NaOH}\) and \(\mathrm{Mg}(\mathrm{OH})_{2}\) weak bases?

Short answer

Ionic compounds like NaOH and Mg(OH)₂ are not considered weak bases because they completely dissociate in water, forming a high concentration of hydroxide ions. This makes them strong bases, as weak bases are characterized by incomplete dissociation and an equilibrium between the base molecule and its ions.

Step-by-step solution

1. Definition of Weak and Strong Bases

A weak base is a base that does not completely dissociate in water, meaning not all the base molecules break apart into their ions. This results in an equilibrium between the base molecule and its ions. A strong base, on the other hand, is a base that completely dissociates in water, meaning all the base molecules break apart into their ions.

2. Ionic Compounds

Ionic compounds are formed when a metal and a nonmetal combine, resulting in a compound held together by ionic bonds. Ionic bonds form when atoms transfer electrons to achieve a stable electron configuration. In the case of NaOH, a sodium ion (\(\mathrm{Na^+}\)) forms an ionic bond with a hydroxide ion (\(\mathrm{OH^-}\)).

3. Dissociation of NaOH and Mg(OH)₂

When ionic compounds dissolve in water, they dissociate into their constituent ions. For example, when sodium hydroxide (\(\mathrm{NaOH}\)) dissolves in water, it dissociates into sodium (\(\mathrm{Na^+}\)) ions and hydroxide (\(\mathrm{OH^-}\)) ions. The same process occurs for magnesium hydroxide (\(\mathrm{Mg(OH)_2}\)), which dissociates into magnesium (\(\mathrm{Mg^{2+}}\)) ions and two hydroxide (\(\mathrm{OH^-}\)) ions. \[ \mathrm{NaOH \rightarrow Na^+ + OH^-} \] \[ \mathrm{Mg(OH)_2 \rightarrow Mg^{2+} + 2OH^-} \]

4. Strong Base Character

As ionic compounds, both NaOH and Mg(OH)₂ dissociate completely into their respective ions in water. Since the solutions of these ionic compounds contain a high concentration of hydroxide (\(\mathrm{OH^-}\)) ions, they are considered strong bases. The complete dissociation of NaOH and Mg(OH)₂ means that they are not in equilibrium with their ions, which is a characteristic of weak bases. In conclusion, ionic compounds like NaOH and Mg(OH)₂ are not considered weak bases because they dissociate completely in water and form a high concentration of hydroxide ions, making them strong bases.

Key concepts

Weak Bases

Weak bases are substances that do not completely dissociate in water. In simple terms, when you dissolve a weak base in water, only a portion of its molecules split into ions. This partial dissociation leads to an equilibrium being established between the undissociated molecules and the ions that have dissociated.
This is why weak bases typically have a lower concentration of hydroxide ions in solution. This incomplete ionization means they react less readily compared to strong bases. A classic example of a weak base is ammonia ( H_3N ), which only partially releases hydroxide ions in water.

Strong Bases

Strong bases are the opposite of weak bases in terms of dissociation. When a strong base dissolves in water, it completely splits into its ions. As a result, the concentration of hydroxide ions ( OH^- ) in the solution is very high.
This full dissociation is what contributes to the strong base's strength. Examples of such bases, like sodium hydroxide ( NaOH ) and potassium hydroxide ( KOH ), are commonly used in various chemical processes because of their potent ability to produce hydroxide ions readily.

Dissociation

Dissociation is the process through which a compound breaks down into its individual ions when dissolved in water. The level of dissociation of a substance can determine whether it behaves as a strong or weak electrolyte.
For example, when NaOH is dissolved in water, it disintegrates completely, resulting in freely moving Na^+ and OH^- ions in the solution. This complete breakdown is a hallmark of strong bases. On the other hand, weak bases only partially dissociate, resulting in an equilibrium state between the ions and the unchanged molecules.

Ionic Bonds

Ionic bonds form when one atom donates an electron to another atom, resulting in the formation of ions. This type of bond is strong and holds ionic compounds together.
Ionic compounds consist of metals and nonmetals. Take the ionic compound NaOH , for instance; it is formed by a strong ionic bond between the sodium ion ( Na^+ ) and the hydroxide ion ( OH^- ). These compounds, being ionic, often dissolve in water and readily dissociate into their constituent ions. This dissociation leads to solutions that can conduct electricity due to the mobility of ions.