Concentration Changes & Acid-Base Concepts

Concentration Changes During Assessment

During an assessment, there must be an abrupt change in some property of the reaction mixture at the equivalence point. The property that changes depends on the volumetric reaction:

• Acid-base: An acid is titrated with a base, or vice versa. The abrupt change is due to a slight excess of one reactant, producing a sudden change in pH.
• Redox: An oxidant is titrated with a reducing agent, or vice versa. The abrupt change is due to a slight excess of one reactant, leading to a sudden change in the cell potential formed by two electrodes.
• Precipitation: An ionic substance is titrated with a precipitating reagent. The abrupt change is due to an excess of the precipitating reagent, which causes a sharp decrease in the concentration of the precipitated ion.

Acid-Base Concepts

Arrhenius Definition

• Acid: Any substance capable of producing H⁺ (H₃O⁺, HCl).
• Base: Any substance capable of producing OH^- (NaOH).

Brønsted-Lowry Definition

• Acid: Any substance that can donate protons (NH₄⁺).
• Base: Any substance that can accept protons (NH₃).

Lewis Definition

• Acid: Any substance capable of accepting an electron pair.
• Base: Any substance capable of donating an electron pair.

Concentration Changes During Assessment

During an assessment, there must be an abrupt change in some property of the reaction mixture at the equivalence point. The property that changes depends on the volumetric reaction:

• Acid-base: An acid is titrated with a base, or a base with an acid. The abrupt change is due to a slight excess of one reactant that produces a sudden change in pH.
• Redox: An oxidant is titrated with a reducing agent or vice versa. The abrupt change is due to a slight excess of one reactant, leading to a sudden change in the cell potential formed by two electrodes.
• Precipitation: An ionic substance is titrated with a precipitating reagent. The abrupt change is due to an excess of the precipitating reagent that produces a sharp decrease in the concentration of the precipitated ion.

Acid-Base Concepts

Arrhenius Definition

• Acid: Any substance capable of producing H⁺ (H₃O⁺, HCl).
• Base: Any substance capable of producing OH^- (NaOH).

Brønsted-Lowry Definition

• Acid: Any substance that can donate protons (NH₄⁺).
• Base: Any substance that can accept protons (NH₃).

Lewis Definition

• Acid: Any substance capable of accepting an electron pair.
• Base: Any substance capable of donating an electron pair.