Water

Definition

Water is a ubiquitous and essential compound found throughout the natural world, playing a crucial role in the Brønsted-Lowry definition of acids and bases. As the universal solvent, water facilitates the dissociation of ionic compounds and the proton transfer reactions that define acid-base chemistry.

5 Must Know Facts For Your Next Test

1. Water can act as both an acid and a base in the Brønsted-Lowry definition, depending on the context of the reaction.
2. The self-ionization of water produces hydronium ions (H3O+) and hydroxide ions (OH-), which are the key players in acid-base equilibria.
3. The pH scale is a measure of the concentration of hydrogen ions (H+) in a solution, with water having a neutral pH of 7.
4. Acids and bases can be classified as strong or weak based on their ability to dissociate in water and the extent of proton transfer.
5. The presence of water is essential for many acid-base reactions to occur, as it provides the medium for the necessary proton transfers.

Review Questions

• Explain how water can act as both an acid and a base in the Brønsted-Lowry definition of acids and bases.
  • In the Brønsted-Lowry definition, an acid is a proton (H+) donor, and a base is a proton acceptor. Water can act as both an acid and a base, depending on the context of the reaction. When water reacts with itself, it undergoes self-ionization, forming hydronium ions (H3O+) and hydroxide ions (OH-). In this case, water acts as an acid by donating a proton to another water molecule, which then acts as the base by accepting the proton. Conversely, water can also act as a base by accepting a proton from a stronger acid, forming a hydronium ion.
• Describe the role of water in the pH scale and the self-ionization of water.
  • The pH scale is a measure of the concentration of hydrogen ions (H+) in a solution, with a neutral pH of 7 corresponding to the concentration of H+ in pure water. This is because water undergoes self-ionization, where a small fraction of water molecules dissociate into hydronium ions (H3O+) and hydroxide ions (OH-). The equilibrium constant for this reaction, known as the ion product of water (Kw), is a fundamental property that determines the pH of a solution. The presence of water is essential for this self-ionization process, as it provides the medium for the necessary proton transfers that define acid-base chemistry.
• Analyze the importance of water in facilitating acid-base reactions and the classification of acids and bases as strong or weak.
  • Water is a crucial component in the Brønsted-Lowry definition of acids and bases, as it provides the medium for the necessary proton transfer reactions to occur. The presence of water allows for the dissociation of ionic compounds and the subsequent formation of hydronium and hydroxide ions, which are the key players in acid-base equilibria. Furthermore, the ability of a substance to dissociate in water and the extent of proton transfer determine whether an acid or base is classified as strong or weak. Strong acids and bases readily dissociate in water, while weak acids and bases only partially dissociate, leading to different equilibrium concentrations of H+ and OH- ions. This classification is essential for understanding the behavior and properties of various acids and bases in aqueous solutions.

Related terms

Acid: A substance that donates protons (H+) in a chemical reaction, increasing the concentration of hydrogen ions in a solution.

Base: A substance that accepts protons (H+) in a chemical reaction, decreasing the concentration of hydrogen ions in a solution.

Proton Transfer: The movement of a hydrogen ion (H+) from one molecule or ion to another, a key process in acid-base reactions.