Question

Identify each as a strong base or a weak base. Assume aqueous solutions. a) \(\mathrm{NaOH}\) b) \(\mathrm{Al}(\mathrm{OH})_{3}\) c) \(\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{NH}_{2}\)

Short answer

a) Strong base b) Weak base c) Weak base

Step-by-step solution

Define Strong and Weak Bases

A strong base is one that completely dissociates into its ions in water. Conversely, a weak base only partially dissociates in water, establishing an equilibrium between the formed ions and the undissociated base.

Analyze \\( \mathrm{NaOH} \\\\)

Sodium hydroxide (NaOH) is a common strong base. When dissolved in water, it completely dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻). Therefore, \( \mathrm{NaOH} \) is considered a strong base.

Analyze \\( \mathrm{Al(OH)_3} \\\\)

Aluminum hydroxide (\( \mathrm{Al(OH)_3} \)) is insoluble in water and only sparingly dissociates. It forms very little hydroxide ion in solution, so it acts as a weak base.

Analyze \\( \mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2 \\\\)

Butylamine (\( \mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2 \)) is an organic amine and a weak base. It partially accepts protons in water, establishing an equilibrium between the protonated and non-protonated forms, typical of weak bases.

Key concepts

Aqueous Solutions

In an aqueous solution, the solvent is water. This means that the substance being dissolved is dispersed in water, making the water molecules the primary environment surrounding the dissolved particles. Water is an excellent solvent due to its polarity, which means it has a partial positive charge on one side and a partial negative charge on the other. This allows water to interact with and stabilize charged particles, such as ions, which form when bases dissociate.

When a base is introduced into an aqueous solution, it interacts with water molecules. Some bases fully dissociate into ions, while others only do so partially. This level of dissociation is a key characteristic that helps to categorize bases as either strong or weak.

• Strong bases, like sodium hydroxide \(\mathrm{NaOH}\), completely dissociate in water, resulting in a clear separation into ions.
• Weak bases, like butylamine \(\mathrm{C}_{4}\mathrm{H}_{9}\mathrm{NH}_{2}\), only partially dissociate, balancing between the ionized and non-ionized forms.

Understanding how substances behave in aqueous solutions is crucial for predicting their reactivity and how they will interact with other substances.

Chemical Dissociation

Chemical dissociation refers to the process where compound molecules break down into smaller units, such as ions, when dissolved in water. This process is pivotal for understanding the behavior of bases in solutions.

Strong bases undergo complete dissociation. Every molecule of the compound separates into ions. For example:

• Sodium hydroxide \(\mathrm{NaOH}\) dissociates into \(\mathrm{Na}^+\) and \(\mathrm{OH}^-\) ions.

This process increases the concentration of hydroxide ions \(\mathrm{OH}^-\) in the solution dramatically.

Contrarily, weak bases undergo partial dissociation. For instance:

• Aluminum hydroxide \(\mathrm{Al(OH)_3}\) is insoluble and only a fraction of it forms \(\mathrm{OH}^-\) ions in water.
• Butylamine \(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2\) merely accepts protons to form an equilibrium between ionized and non-ionized molecules.

The extent of dissociation affects everything from pH levels to reactivity, and is vital for predicting chemical behaviors in various reactions.

Chemical Equilibrium

Chemical equilibrium is a fundamental concept in the study of weak bases. It occurs when the forward reaction rate, where reactants form products, equals the reverse reaction rate, where products form reactants.

In the context of weak bases, equilibrium is established because these compounds do not fully dissociate. Weak bases, like butylamine \(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2}\), reach an equilibrium between the dissociated ions and the non-dissociated molecules.

The equilibrium can be represented by:

• For butylamine, when in water, the equilibrium exists between \(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_2\) and \(\mathrm{C}_4\mathrm{H}_9\mathrm{NH}_3^+\) plus \(\mathrm{OH}^-\).

In this scenario, not all amine molecules dissociate, leading to an equilibrium state.

Understanding chemical equilibrium helps predict how systems respond to changes, such as concentration alterations or changes in pH. This is crucial in chemical reactions involving weak bases, as equilibrium principles dictate the concentration of ions in any given solution.