Question

Restate the Arrhenius definition of a base and demonstrate the definition with a chemical equation.

Short answer

An Arrhenius base is a substance that increases the concentration of hydroxide ions (OH^-) in water, demonstrated by the dissociation of sodium hydroxide: NaOH (s) -> Na^+ (aq) + OH^- (aq).

Step-by-step solution

Understanding the Arrhenius Definition of a Base

According to the Arrhenius definition, a base is a substance that increases the concentration of hydroxide ions (OH^-) when dissolved in water. This increase in hydroxide ion concentration results in a more alkaline, or basic, solution.

Writing a Chemical Equation for an Arrhenius Base

To demonstrate the Arrhenius definition with a chemical equation, consider sodium hydroxide (NaOH), a common base. When sodium hydroxide dissolves in water, it dissociates into sodium ions (Na^+) and hydroxide ions (OH^-), which increases the hydroxide ion concentration in the solution. The chemical equation for this process is: NaOH (s) -> Na^+ (aq) + OH^- (aq).

Key concepts

Understanding Hydroxide Ions

In chemistry, hydroxide ions are fundamental to the behavior of bases. They consist of one oxygen atom bonded to a hydrogen atom and carry a negative charge, represented by the symbol \(OH^-\). An increased presence of these ions in an aqueous solution is characteristic of a basic environment. Hydroxide ions play a crucial role in various chemical processes, including neutralization reactions where they combine with hydrogen ions \(H^+\) to form water \(H_2O\).

A common exercise when studying acids and bases involves identifying the increase in hydroxide ion concentration caused by dissolving a base in water. This increase, which raises the solution's pH, can be measured using indicators or pH meters, and is essential in many industrial and biological processes. As part of their chemical nature, hydroxide ions are also responsible for the slippery feel of soapy water and the corrosive nature of certain basic solutions.

Chemical Equations for Bases

The representation of a base in action is neatly encapsulated in a chemical equation. This equation illustrates the process by which a base produces hydroxide ions in an aqueous solution.

Example of a Base Dissociating

A classic example of such a dissociation, as mentioned in the original exercise, involves sodium hydroxide \(NaOH\):

\[ NaOH \_(s) \rightarrow Na^+ \_(aq) + OH^- \_(aq) \]
In this equation, the solid sodium hydroxide dissociates to form sodium ions and hydroxide ions when dissolved in water. The \(aq\) symbols indicate that the ions are in an aqueous state—that is, they are solvated by water molecules. Demonstrations of this kind serve not only to reinforce the understanding of the Arrhenius definition of bases but also to familiarize students with the process of dissociation, which is key in predicting the behavior of substances in a solution.

Properties of Bases

Bases exhibit certain properties which differentiate them from other types of chemical substances, and these characteristics are observable through laboratory experiments and everyday encounters.

Sensory Characteristics

For instance, bases tend to feel slippery and can be soapy to the touch, which is why substances like sodium hydroxide are used in soap making. They also have a bitter taste, although tasting them is highly discouraged due to the risk of toxicity and tissue damage.

Chemical Reactions

On the chemical side, bases neutralize acids producing water and salt in a chemical reaction, which makes them valuable in various applications ranging from antacid formulations for gastric relief to industrial cleaners.

pH and Indicators

Furthermore, bases will turn red litmus paper to blue and make phenolphthalein indicator solution pink, indicating the presence of hydroxide ions.

These properties are not just academic concepts but are fundamentally critical in different industries like pharmaceuticals, agriculture, and manufacturing where the manipulation of basic solutions is necessary for product development and quality control.