Question

(a) Given that \(K_{b}\) for ammonia is \(1.8 \times 10^{-5}\) and that for hydroxylamine is \(1.1 \times 10^{-8}\), which is the stronger base?

Short answer

Ammonia is the stronger base because it has a higher \(K_b\) value (\(1.8 \times 10^{-5}\)) compared to hydroxylamine (\(1.1 \times 10^{-8}\)).

Step-by-step solution

Write down the given \(K_b\) values for both bases

The \(K_b\) value for ammonia is given as \(1.8 \times 10^{-5}\) and for hydroxylamine, it is \(1.1 \times 10^{-8}\).

Compare the \(K_b\) values

We need to compare \(K_b\) values for both bases to find out which one is stronger. - \(K_{b} (\text{ammonia}) = 1.8 \times 10^{-5}\) - \(K_{b} (\text{hydroxylamine}) = 1.1 \times 10^{-8}\)

Identify the stronger base

Since \(K_{b} (\text{ammonia}) > K_{b}(\text{hydroxylamine}) \), ammonia is the stronger base.

Key concepts

Kb value

The K_b value, or base dissociation constant, is a numerical expression representing the strength of a base in solution. It measures a base's propensity to accept protons (H+) from water, forming OH- ions and the corresponding conjugate acid. In simpler terms, higher K_b values correspond to stronger bases.

When comparing the base strength using K_b values, it's important to realize that these are exponential numbers. Thus, even small numerical differences can indicate significant strength discrepancies because they represent orders of magnitude.

Ammonia

Ammonia, NH₃, is a common weak base used in various chemical applications. Despite being categorized as 'weak', it has a relatively high K_b value for such bases, and it readily accepts protons to form NH₄⁺ when dissolved in water. This reaction is fully reversible, which is typical for weak bases, leading to an equilibrium state described by its K_b value. Ammonia's characteristic pungent smell and its ability to form strong hydrogen bonds make it easily recognizable in both the laboratory and everyday life.

Hydroxylamine

Hydroxylamine, NH₂OH, shares structural similarities with ammonia but has a hydroxyl group (-OH) instead of one hydrogen atom. This compound is also a weak base but has a much lower K_b value than ammonia, indicating that it is less inclined to accept protons from water to form its conjugate acid, NH₃OH⁺. This property can affect its behavior in chemical reactions, especially those involving acid-base equilibria. Despite its lower base strength, hydroxylamine is impactful in various organic and inorganic reactions.

Acid-base equilibrium

Acid-base equilibrium refers to the state where the rates of the forward and reverse reactions between acids and bases are equal, resulting in no net change in the concentrations of the reactants and products. This concept is encapsulated in the K_b value for bases and the K_a value for acids. In an aqueous solution, a weak base like ammonia or hydroxylamine partially dissociates, and the reaction reaches an equilibrium point. Understanding this equilibrium is crucial for predicting the pH of solutions and the outcome of reactions in which the acid-base property plays a fundamental role.

Moreover, the acid-base equilibrium is influenced by factors such as temperature, concentration, and the presence of other species in solution. These factors can shift the equilibrium, thereby changing the pH and the strengths of acids and bases in a given reaction environment.