pH and Hydrogen Ion Concentration

This section explores the relationship between pH and hydrogen ion concentration in water. It provides key formulas and definitions related to acids and bases.

Definition: pH = -log10[H3O+] and [H3O+] = 10^-pH

These formulas show the inverse logarithmic relationship between pH and hydrogen ion concentration. In neutral water at 25°C, both [H3O+] and [OH-] are 10^-7 mol/L.

The Brønsted-Lowry definition of acids and bases is introduced:

• Acids are proton donors
• Bases are proton acceptors

Vocabulary: Conjugate base is the species left when an acid donates a proton. Conjugate acid is formed when a base accepts a proton.

The text distinguishes between strong and weak acids/bases:

• Strong acids/bases fully dissociate in water (e.g., HCl, NaOH)
• Weak acids/bases partially dissociate in water (e.g., ethanoic acid, ammonia)

A table compares properties of strong and weak acids/bases, including pH values, conductivity, and reaction rates.

Acid Dissociation Constants and Salt Solutions

This page delves deeper into weak acids and bases, introducing the concept of acid dissociation constants (Ka) and their relationship to pH.

Definition: Ka is the equilibrium constant for the dissociation of a weak acid in water.

The Ka value measures the strength of a weak acid. A smaller Ka indicates a weaker acid. The pKa, defined as the negative logarithm of Ka, is often used in calculations.

Highlight: pH = pKa - log C (where C is the concentration of the weak acid)

The formation of salts from acid-base reactions is discussed. The pH of salt solutions depends on the strength of the parent acid and base:

• Strong acid + strong base = neutral solution
• Weak acid + strong base = alkaline solution
• Strong acid + weak base = acidic solution

Example: NaCl (from HCl + NaOH) produces a neutral solution, while CH3COONa (from CH3COOH + NaOH) produces an alkaline solution.

This information helps in understanding the behavior of various salt solutions and their applications in chemistry and related fields.

Partition Coefficients and Solvent Extraction

This page covers partition coefficients and their application in solvent extraction, an important purification technique in chemistry.

The partition coefficient describes how a solute distributes between two immiscible liquids. It is temperature-dependent but unaffected by adding more solvent or solute.

Example: The partition coefficient formula for sodium chloride between water and hexane is: K = [salt(hexane)] / [salt(aq)]

Solvent extraction, a common application of partition coefficients, is used for purifying chemicals.

Highlight: It is more efficient to use small volumes of organic solvent in repeated extractions rather than one large volume in a single extraction.

The section also introduces acids and bases, explaining that hydrogen ions (H+) form hydronium ions (H3O+) in water. Water's amphoteric nature and its ionic product (Kw) are discussed.

Vocabulary: Amphoteric substances can behave as both acids and bases.