1 CHAPTER 4 CHAPTER 4 AQUEOUS REACTIONS & SOLUTION STOICHIOMETRY
2 CONTENTS 4.1 General Properties of Aqueous Solutions 4.2 Precipitation Reactions 4.3 Acid-Base Reactions 4.4 Oxidation-Reduction Reactions 4.5 Concentrations of Solutions 4.6 Solution Stoichiometry and Chemical Analysis
3 Learning Outcomes ＊ Able to identify types of metathesis reaction ＊ Able to determine the precipitate forms in a reaction ＊ Able to calculate oxidation number of element and identify the oxidizing agent in a redox reaction ＊ Able to calculate unknown concentration in a titration of acid-base solutions (reaction).
4 4.1 General Properties of Aqueous Solutions • A solution is a homogeneous mixture. • Contains: a solvent (greater quantity) and solute(s). • Solvent - substance in the mixture which acts as the dissolving medium. • Whatever else is dissolved in the solution is called the solute(s) .
5 Con’t: 4.1 General Properties of Aqueous Solutions • E.g. NaCl (s) + H 2 O (l) NaCl (aq) solute solvent aqueous solution • Solution in which water is the dissolving medium are called aqueous solutions .
6 Con’t: 4.1 General Properties of Aqueous Solutions All aqueous solutions can be classified in terms of its electrical conductivity. • Solution conducts electricity: – forms ions in solution – is an electrolyte . e.g. NaCl (an ionic compound ) # conducts electricity well: strong electrolyte (NaCl) # conducts electricity poorly: weak electrolytes (CH 3 COOH)
7 Con’t: 4.1 General Properties o Aqueous Solutions • Solution does not conduct electricity – does not form ions in solution – is a non electrolyte e.g. sugar (a molecular compound)
8 4.1.1 Ionic Compounds in Water • Ionic compounds dissolve in water, dissociate into anions and cations. • The solid no longer exists as a well ordered arrangement, each ion is surrounded by water molecules . • The ions are dispersed uniformly throughout the solution. • The relative concentrations of the ions depend on the chemical formula of the compound. (Sec: 4.5.2)
» H 2 O 9
11 4.1.2 Molecular Compounds in Water • Molecular compounds (e.g. CH 3 OH, sugar etc.) dissolve and exist as dispersed molecules throughout the solution. • The structural integrity of the compound is maintained. • Does not form ions – no ions to conduct electricity. they are non-electrolytes
NaCl in water 12
13 Con’t: 4.1.2 Molecular Compounds in Water • Some important exceptions: NH 3 dissolves in water to form NH 4 + and OH - HCl (g) in water ionizes to form H + and Cl -
14 4.1.3 Strong and Weak Electrolytes • Electrolyte: any substance whose aqueous solution contains ions that conduct electricity. • Strong electrolytes - ionize 100 % in a solvent. E.g. (i) Most ionic compounds (salt) (ii) Strong acids and bases: HCl, HBr, HClO 4 • A single arrow ( ): ionization of strong electrolytes.
- Spring '09
- Chemistry, Chemical reaction