When an acid dissolves in water, it releases hydrogen ions (H⁺), causing the solution to become more acidic.
The Core Process: Ionization
Acids are substances that exhibit acidic properties when in the presence of water. This is primarily due to a chemical reaction where the acid molecule interacts with water and breaks apart, a process known as ionization or dissociation.
According to the reference provided, when an acid is dissolved in water, it furnishes hydrogen ions, and consequently, the concentration of hydrogen ions increases in the solution. This increase in mobile hydrogen ions is the fundamental event.
For instance, consider a generic acid represented as HA:
HA (acid) + H₂O (water) → H⁺ (hydrogen ion) + A⁻ (anion)
Note: In water, H⁺ ions quickly combine with water molecules to form hydronium ions (H₃O⁺), so the equation is often written as HA + H₂O → H₃O⁺ + A⁻. However, the core concept is the release and increased concentration of the species responsible for acidity – the hydrogen ion.
Consequences of Increased Hydrogen Ions
The elevated concentration of H⁺ ions dramatically changes the properties of the water solution:
- Increased Acidity: The solution exhibits acidic characteristics, such as a sour taste (though you should never taste chemicals).
- Lowered pH: The pH scale is a measure of hydrogen ion concentration. An increase in H⁺ concentration results in a decrease in the pH value. Acidic solutions have a pH less than 7.
- Electrical Conductivity: The presence of charged particles (ions like H⁺ or H₃O⁺ and the acid's anion, A⁻) allows the solution to conduct electricity.
Strength of Acids
Acids are classified based on the extent to which they ionize in water:
- Strong Acids: These acids ionize almost completely in water, releasing nearly all their hydrogen ions. Examples include sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
- Weak Acids: These acids only partially ionize, meaning only a fraction of their molecules release hydrogen ions. Examples include acetic acid (CH₃COOH) and carbonic acid (H₂CO₃).
Even with weak acids, the process still involves furnishing hydrogen ions and increasing their concentration, just to a lesser degree than strong acids.
Summary
| What happens to the acid? | What happens to the water solution? | Key result (from reference) |
|---|---|---|
| Dissociates / Ionizes | Becomes acidic | Furnishes hydrogen ions |
| Releases H⁺ ions | pH decreases | Concentration of hydrogen ions increases in the solution |
| Forms anions | May conduct electricity |
In essence, dissolving an acid in water triggers its dissociation, releasing hydrogen ions, which directly leads to an increase in the hydrogen ion concentration and makes the solution acidic.
