Which of the following statements is correct when an acid is dissolved in water?

a) The separation of H⁺ ions from HCl molecules cannot occur in the absence of water.

b) Hydrogen ions must always be shown as ⁺ (aq) or hydronium ion (H₃O⁺). 

The Correct answer is Both a and b.

Key Points

• The separation of H+ ions from HCl molecules indeed cannot occur in the absence of water. Water is necessary to facilitate the dissociation process.
• Hydrogen ions in an aqueous solution are always shown as H+ (aq) or H3O+ (hydronium ion). This is because hydrogen ions cannot exist freely in water; they combine with water molecules to form hydronium ions.
• When an acid like HCl is dissolved in water, it dissociates into H+ (aq) and Cl- (aq), demonstrating the necessity of water for this process.
• The correct representation of hydrogen ions in water as H+ (aq) or H3O+ ensures a more accurate depiction of their behavior in solution.
• Both statements are correct and together they provide a comprehensive understanding of the behavior of acids in water.

 Additional Information

• Hydronium Ion (H3O+)
  • The hydronium ion is formed when a water molecule accepts a hydrogen ion (proton).
  • It plays a key role in the chemistry of acids and bases in aqueous solutions.
  • Hydronium ions are responsible for the acidic properties of solutions.
• Dissociation in Water
  • Dissociation is the process by which molecules split into smaller particles such as ions.
  • This process is crucial in understanding the behavior of acids, bases, and salts in water.
  • Water acts as a solvent and facilitates the dissociation of ionic compounds.