Question

Write an equation showing how $\mathrm{HCl}(g)$ behaves as an Arrhenius acid when dissolved in water. Write an equation showing how $\mathrm{NaOH}(s)$ behaves as an Arrhenius base when dissolved in water.

Short answer

HCl(g) behaves as an Arrhenius acid when dissolved in water through the following reaction: $HCl(g)+H_{2}O(l)\to H_3{O}^{+}(aq)+C{l}^{-}(aq)$. NaOH(s) behaves as an Arrhenius base when dissolved in water through the following reaction: $NaOH(s)\to N{a}^{+}(aq)+O{H}^{-}(aq)$.

Step-by-step solution

Equation 1: HCl(g) as an Arrhenius acid

To show how HCl(g) behaves as an Arrhenius acid when dissolved in water, we need to write an equation that shows the formation of hydrogen ions (H+). The equation will be the reaction between HCl(g) and water: $$HCl(g)+H_{2}O(l)\to H_3{O}^{+}(aq)+C{l}^{-}(aq)$$ In this reaction, HCl(g) donates a proton (H+) to the water molecule, forming hydronium ions (H3O+) and chloride ions (Cl-). This increase in H+ concentration demonstrates that HCl(g) behaves as an Arrhenius acid when dissolved in water.

Equation 2: NaOH(s) as an Arrhenius base

To show how NaOH(s) behaves as an Arrhenius base when dissolved in water, we need to write an equation that shows the formation of hydroxide ions (OH-). The equation will be the reaction between NaOH(s) and water: $$NaOH(s)\to N{a}^{+}(aq)+O{H}^{-}(aq)$$ In this reaction, NaOH(s) dissolves in water and dissociates into sodium ions (Na+) and hydroxide ions (OH-). This increase in OH- concentration demonstrates that NaOH(s) behaves as an Arrhenius base when dissolved in water.

Key concepts

Chemical Equations and Reaction Representations

Understanding chemical equations is fundamental in the study of chemistry. They are a shorthand way to represent what happens in a chemical reaction. It’s like a recipe that chemists use to communicate the substances involved in chemical processes. In the context of Arrhenius acids and bases, these equations are particularly useful for illustrating the changes that occur when these substances dissolve in water.

For example, when hydrochloric acid (HCl) gas is introduced to water, we can depict what happens using a chemical equation. It is important to note that the reactants (HCl and H₂O) and the products (H₃O⁺ and Cl^-) must be balanced. This balancing act is not just a mere formality; it reflects the conservation of mass and charge. Each atom on the left side of the arrow in a chemical equation needs to be accounted for on the right side, in the same manner that you would ensure every ingredient listed in a recipe is used.

In summary, always check that the number of atoms for each element, and the overall charge, is the same on both sides of the equation. This skill is essential in understanding how chemicals interact with each other, especially in the realm of acid-base reactions.

Dissociation of Acids and Bases in Water

The concept of dissociation is crucial when discussing Arrhenius acids and bases. Dissociation refers to the process by which a compound breaks down into its constituent ions when it is dissolved in water. This process is key to understanding how these substances alter the pH level of a solution.

An Arrhenius acid like HCl dissociates to produce hydrogen ions (H⁺), also depicted as hydronium ions (H₃O⁺), while Arrhenius bases such as NaOH dissociate to produce hydroxide ions (OH^-). This dissociation is a physical representation of how acids and bases behave in water; acids increase the concentration of H₃O⁺, while bases increase the concentration of OH^-.

To improve comprehension, it's valuable to visualize dissociation as the 'untying' of ions that were previously 'tied' together in a solid state. The water's role as a solvent provides the energy needed to 'unbind' these ions. By comparing this process to untying a knot, students may find it easier to grasp the concept of dissociation in acid-base chemistry.

Hydronium Ion Formation in Water

The formation of the hydronium ion (H₃O⁺) is a characteristic action of Arrhenius acids in water. It's not just the release of any hydrogen ion, but specifically the hydrogen ion's interaction with water molecules that defines this process. A hydronium ion is formed when a water molecule bonds with a hydrogen ion (H⁺), which results from the acid's dissociation.

It’s akin to a social gathering where a new guest (the hydrogen ion) is quickly welcomed and surrounded by water molecules, forming a new entity (the hydronium ion). This interaction is essential because it influences the acidity of a solution. As the concentration of hydronium ions increases, so does the acidity.

To solidify understanding, one might think of hydronium ions as the 'footprint' left by an acid in water. The more prominent the footprint, the stronger the acid's presence in the solution. Emphasizing the role of water in forming hydronium ions can help students appreciate the dynamic nature of chemical reactions in aqueous solutions.