Question

Write a chemical equation showing how each of the following species can behave as indicated when dissolved in water. a. \(\mathrm{O}^{2-}\) as a base b. \(\mathrm{NH}_{3}\) as a base c. \(\mathrm{HSO}_{4}^{-}\) as an acid d. \(\mathrm{HNO}_{2}\) as an acid

Short answer

a. \( \mathrm{O}^{2-} \,+\, \mathrm{H}_{2}\mathrm{O} \,\rightleftharpoons\, 2 \,\mathrm{OH}^- \) b. \( \mathrm{NH}_{3} \,+\, \mathrm{H}_{2}\mathrm{O} \,\rightleftharpoons\, \mathrm{NH}_{4}^{+} \,+\, \mathrm{OH}^- \) c. \( \mathrm{HSO}_{4}^{-} \,+\, \mathrm{H}_{2}\mathrm{O} \,\rightleftharpoons\, \mathrm{SO}_{4}^{2-} \,+\, \mathrm{H}_{3}\mathrm{O}^{+} \) d. \( \mathrm{HNO}_{2} \,+\, \mathrm{H}_{2}\mathrm{O} \,\rightleftharpoons\, \mathrm{NO}_{2}^{-} \,+\, \mathrm{H}_{3}\mathrm{O}^{+} \)

Step-by-step solution

a. O²⁻ as a base

When \(\mathrm{O^{2-}}\) behaves as a base, it accepts a proton from the water molecule, forming hydroxide ions, \(\mathrm{OH}^{-}\) and the final balanced chemical equation is: \[ \mathrm{O}^{2-} \,+\, \mathrm{H}_{2}\mathrm{O} \,\rightleftharpoons\, 2 \,\mathrm{OH}^- \]

b. NH₃ as a base

When \(\mathrm{NH}_{3}\) behaves as a base, it accepts a proton from the water molecule, forming the ammonium ion, \(\mathrm{NH}_{4}^{+}\). The balanced chemical equation is: \[ \mathrm{NH}_{3} \,+\, \mathrm{H}_{2}\mathrm{O} \,\rightleftharpoons\, \mathrm{NH}_{4}^{+} \,+\, \mathrm{OH}^- \]

c. HSO₄⁻ as an acid

When \(\mathrm{HSO}_{4}^{-}\) behaves as an acid, it donates a proton to the water molecule, forming the hydronium ion, \(\mathrm{H}_{3}\mathrm{O}^{+}\) and sulfate ion, \(\mathrm{SO}_{4}^{2-}\). The balanced chemical equation is: \[ \mathrm{HSO}_{4}^{-} \,+\, \mathrm{H}_{2}\mathrm{O} \,\rightleftharpoons\, \mathrm{SO}_{4}^{2-} \,+\, \mathrm{H}_{3}\mathrm{O}^{+} \]

d. HNO₂ as an acid

When \(\mathrm{HNO}_{2}\) behaves as an acid, it donates a proton to the water molecule, forming the hydronium ion, \(\mathrm{H}_{3}\mathrm{O}^{+}\) and nitrite ion, \(\mathrm{NO}_{2}^{-}\). The balanced chemical equation is: \[ \mathrm{HNO}_{2} \,+\, \mathrm{H}_{2}\mathrm{O} \,\rightleftharpoons\, \mathrm{NO}_{2}^{-} \,+\, \mathrm{H}_{3}\mathrm{O}^{+} \]

Key concepts

Chemical Equation

In chemistry, a chemical equation is a symbolic representation that displays the reactants and products of a chemical reaction. It shows how substances transform or interact.
It comprises chemical formulas for each participant within the equation. Additionally, it indicates their relative quantities through coefficients.
Take, for example, the chemical equation for \ \[ \mathrm{O}^{2-} + \mathrm{H}_{2}\mathrm{O} \rightleftharpoons 2 \, \mathrm{OH}^- \].

• The reactants, \(\mathrm{O}^{2-} \) and \(\mathrm{H}_2\mathrm{O} \), are on the left side of the arrow.
• The products, \(2 \, \mathrm{OH}^- \), are shown on the right.

A balanced chemical equation ensures the same number of each type of atom on both sides. This conservation adheres to the Law of Conservation of Mass.
Understanding chemical equations is pivotal for studying and predicting chemical reactions, such as acid-base reactions.

Base

In acid-base chemistry, a base is a substance that can accept protons (\(\mathrm{H}^{+}\)) from an acid.
Bases usually have hydroxide ions (\(\mathrm{OH}^-\)) or can generate them when dissolved in water.
For instance, \(\mathrm{NH}_3\) behaves as a base by accepting protons from water:

• \[ \mathrm{NH}_3 + \mathrm{H}_{2}\mathrm{O} \rightleftharpoons \mathrm{NH}_{4}^{+} + \mathrm{OH}^- \]

This reaction results in the formation of ammonium (\(\mathrm{NH}_{4}^{+}\)) and hydroxide ions.
Bases change the pH of a solution by decreasing hydronium ions and increasing hydroxide ions, making the solution more basic or alkaline.
Understanding bases helps us grasp the nature of a wide range of chemical reactions, from cleaning products to physiological processes in the human body.

Acid

Acids are a group of substances that are able to donate protons (\(\mathrm{H}^{+}\)) to other substances in chemical reactions.
A well-known feature of acids is that they release hydrogen ions in aqueous solutions.
For example, when \(\mathrm{HSO_{4}^{-}}\) acts as an acid, it donates a proton to water:

• \[ \mathrm{HSO}_{4}^{-} + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{SO}_{4}^{2-} + \mathrm{H}_3\mathrm{O}^+ \]

This reaction produces sulfate ions (\(\mathrm{SO}_{4}^{2-}\)) and hydronium ions (\(\mathrm{H}_{3}\mathrm{O}^{+}\)).
Acids are characterized by their sour taste and their ability to turn blue litmus paper red in aqueous solutions.
They play a critical role in many natural and industrial processes such as digestion, metal and mineral processing, and synthetic chemistry.

Proton Transfer

Proton transfer is a fundamental concept in acid-base chemistry involving the movement of protons (\(\mathrm{H}^{+}\)) between molecules.
This process is central to understanding how acids and bases react. For instance, in the reaction between \(\mathrm{HNO_2}\) and water:

• \[ \mathrm{HNO}_{2} + \mathrm{H}_{2}\mathrm{O} \rightleftharpoons \mathrm{NO}_{2}^{-} + \mathrm{H}_{3}\mathrm{O}^{+} \]

The proton transfer from \(\mathrm{HNO_2}\) to water results in the formation of \(\mathrm{H}_{3}\mathrm{O}^+\), a quintessential part of acid behavior.
This reaction highlights how acids increase the concentration of hydronium ions in an aqueous solution.
Conversely, bases increase the concentration of \(\mathrm{OH}^{-}\) in solution by accepting protons or releasing them.
Understanding proton transfer is essential for recognizing the behavior of substances in chemical reactions, such as titrations or buffering systems, and predicting their outcomes.