Proton Transfer, Strong and Weak Acid | Chemistry for Grade 11 (IGCSE) PDF Download

Proton transfer 

• The previous definitions of acids and bases can be expanded upon. When we consider proton transfer, we delve deeper into how each substance interacts with protons.
• In the context of proton transfer, we can elaborate on how substances behave regarding proton interactions.

Acids 

• Acids act as proton donors by ionizing in a solution, releasing protons (H⁺ ions). These H⁺ ions contribute to the acidic nature of the solution.
• Proton donors supply H⁺ ions, thereby increasing the acidity of the solution.

Bases 

• Bases function as proton acceptors; they receive protons donated by acids.
• Proton acceptors take in protons provided by acids, playing a crucial role in chemical reactions.
• Diagram showing the role of acids and bases in the transfer of protons - here water acts as a base as it accepts a proton:
  

Strong Acids

• Acids can be categorized as strong or weak based on the number of H⁺ ions they release in water.
• Strong acids completely dissociate in water, resulting in solutions with very low pH levels.
• Examples of strong acids are hydrochloric acid (HCl) and sulfuric acid (H₂SO₄).
• For instance, when hydrochloric acid dissolves in water, it ionizes into H⁺ and Cl^- ions: HCl (aq) → H+ (aq) + Cl- (aq).

Weak Acids

• Weak acids only partially dissociate in water, leading to pH values closer to the middle of the pH scale, below 7.
• Organic acids like ethanoic acid (CH₃COOH) are examples of weak acids.
• When weak acids are added to water, an equilibrium is established between the molecules and their ions.
• For example, propanoic acid undergoes partial ionization in water: CH₃CH₂COOH ⇌ H+ + CH₃CH₂COO^-.
• The equilibrium favors the left side, indicating a high concentration of intact acid molecules with a low concentration of H+ ions in the solution.

Effect of Concentration on Strong and Weak Acids

• A concentrated acid solution has a higher number of acid molecules per dm3 of solution. It does not necessarily denote strength, as it could be from a weak acid that doesn't fully dissociate.
• For instance, a dilute HCl solution can be more acidic than a concentrated ethanoic acid solution, as most HCl molecules dissociate compared to CH₃COOH.