Question

a. What determines the strength of an Arrhenius base? b. Give one example each of an aqueous solution of a strong base and an aqueous solution of a weak base.

Short answer

The strength of an Arrhenius base is determined by its degree of dissociation in water. An example of a strong base is NaOH, and an example of a weak base is NH_3.

Step-by-step solution

Understanding the Strength of an Arrhenius Base

The strength of an Arrhenius base is determined by its ability to dissociate completely in water. Strong bases dissociate fully into metal ions and hydroxide ions \(OH^-\), while weak bases only partially dissociate.

Identify Strong and Weak Bases

Strong bases include substances like \(NaOH\) (sodium hydroxide), \(KOH\) (potassium hydroxide), and \(Ca(OH)_2\) (calcium hydroxide). Weak bases usually include substances like \(NH_3\) (ammonia) and \(CH_3NH_2\) (methylamine).

Example of a Strong Base in Aqueous Solution

An example of an aqueous solution of a strong base is sodium hydroxide (\(NaOH\)) in water. It dissociates completely as \[ NaOH(aq) \rightarrow Na^+(aq) + OH^-(aq) \].

Example of a Weak Base in Aqueous Solution

An example of an aqueous solution of a weak base is ammonia (\(NH_3\)) in water. It dissociates partially as \[ NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq) \].

Key concepts

Base Dissociation

Base dissociation refers to the process through which a base splits into its constituent ions in water. This characteristic is what determines the strength of the base as an Arrhenius base. When a base dissociates, it forms hydroxide ions \(OH^-\) and a corresponding cation.
Strong bases dissociate fully, meaning each molecule separates into ions completely. In contrast, weak bases only partially dissociate, resulting in a mix of ions and original molecules. This distinctive dissociation behavior helps in classifying the base's strength and how it behaves in an aqueous solution.

Strong Bases

Strong bases are substances that completely dissociate when dissolved in water. This means that they ionize 100%, forming hydroxide ions \(OH^-\) and corresponding metal ions.
Common examples include:

• Sodium Hydroxide (NaOH)
• Potassium Hydroxide (KOH)
• Calcium Hydroxide (Ca(OH)_2)

These bases are highly effective in raising pH levels and are used in various industrial and chemical processes. For instance, sodium hydroxide is widely used in cleaning products and manufacturing.

Weak Bases

Weak bases, unlike strong bases, only partially dissociate in aqueous solutions. This partial dissociation means that only a small fraction of the base molecules produce hydroxide ions \(OH^-\), with the rest remaining in their original form.
Common examples of weak bases include:

• Ammonia (NH_3)
• Methylamine (CH_3NH_2)

Weak bases usually result in a much lower increase in pH compared to strong bases. They tend to be less corrosive and are often used where a mild basic effect is required, such as in some cleaning agents and pharmaceuticals.

Sodium Hydroxide

Sodium hydroxide (NaOH) is one of the most well-known strong bases. In an aqueous solution, it dissociates completely as:
\[ NaOH(aq) \rightarrow Na^+(aq) + OH^-(aq) \]
This complete dissociation makes it very effective in neutralizing acids and increasing the pH of solutions.
It is popularly used in a variety of applications, including:

• Manufacturing soap and detergents
• Water treatment
• Food processing
• Paper production

Sodium hydroxide is also known for its caustic properties, requiring careful handling to avoid chemical burns.

Ammonia

Ammonia (NH_3) is a common example of a weak base. In water, it undergoes partial dissociation, which can be represented as:
\[ NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq) \]
Because it does not fully dissociate, the solution contains both ammonia molecules and the ions produced from its reaction with water.
Ammonia is widely used in various fields due to its less aggressive basic properties when compared to strong bases. Common applications include:

• Fertilizers
• Household cleaners
• Refrigerants
• Water treatment

Ammonia solutions are less caustic than strong bases but still need to be handled with care.