Chemistry 141 Monday, October 2, 2017 Lecture 12 Solution Chemistry, Part 2

Objectives for today Begin to gain chemical intuition about reactions in solution Understand the factors that determine solubility and solution conductivity (electrolytes) Predict whether a precipitate will form in a reaction Identify and differentiate between strong and weak acids and bases

Water, the universal solvent Water is a polar molecule There is partial negative charge on the oxygen and partial positive charge on the hydrogens

Dissolving an ionic compound (salt) Consist of a lattice of + (metal) and – (non-metal) ions Dissociate in water into ions Conduct electricity (electrolyte) Cl– Na+ NaCl (s) Na+ (aq) + Cl– (aq)

Dissolving a covalent compound Covalent (molecular) compounds: Consist of neutral atoms (usually non-metals) bonded together in discrete molecules Dissolve in ‘like’ solvents (polar ethanol molecule in polar water) Dissociate very little

Electrolytes A strong electrolyte dissociates completely when dissolved in water; solution conducts electricity (e.g. soluble salts, strong acids and bases) A weak electrolyte only dissociates partially when dissolved in water (e.g., weak acids and bases – conducts weakly) A nonelectrolyte does NOT dissociate in water

Solubility rules Compounds containing the following ions are soluble: - Li+, Na+, K+, Cs+, and NH4+ - nitrates (NO3–), chlorates (ClO3–), and acetates (C2H3O2–) - chlorides (Cl–), bromides (Br–), and iodides (I–) (except those of Ag+, Hg22+, Tl+, and Pb2+) - sulfates (SO42–) (except those of Ca2+, Ba2+, Pb2+, Ag+, and Hg22+) Compounds containing the following ions are insoluble: - sulfides (S2–) (except those of alkali metals, NH4+, Ca2+, and Ba2+) - carbonates (CO32–), phosphates (PO43–), and sulfites (SO32–) (except those of alkali metals and NH4+) - hydroxides (OH–)

Compound types and solubility Ionic (salt) Covalent (molecule) - Made up of + and – ions - Made up of neutral atoms - Consist of metal + nonmetal - Consist of nonmetal + nonmetal - Exist as a continuous lattice of alternating + and – ions - Exist as discrete molecules - Dissociate in water - Dissociate very little in water Solutions conduct electricity (electrolytes) Solutions do not conduct electricity (non-electrolytes) Ionic Polar covalent Non-polar covalent (+2)(-2) (+1)(-1) ethanol hexane dissolves in water? NO YES increasing charge separation (use solubility rules for each case)

Precipitation What happens when aqueous solutions of KCl and AgNO3 are mixed?

Types of solution reactions Precipitation reactions make a solid product, almost always an insoluble salt. Acid–base reactions require both an acid and a base as reactants usually form water as a product Redox reactions characterized by changes in the oxidation states of elements