TYPES of REACTIONS and SOLUTION STOICHIOMETRY Aqueous Solutions and Electrolytes Precipitation, Acid-Base, Oxidation- Reduction (Redox) Reactions

AQUEOUS SOLUTION Water is the solvent, other species (present in small amounts) are the solutes.. Water is polar (there is a charge separation between the O and H atoms) and has a very high capacity to dissolve many compounds. When ionic compounds dissolve in water, an aqueous solution of cations and anions is created. Ions dissolved in water are designated by (aq).

Figure 4.1 The Water Molecule is POLAR (note net partial charges on O and H)

Fig 4.2 Polar H 2 O Molecules Interact with the + and - Ions of a Salt Assisting in the Dissolving Process (hydration)

AQUEOUS SOLUTIONS (2) Electrolytes are cmps that form ions in water and, therefore, conduct electricity. The extent of ionization (solubility) varies from cmp to cmp leading to strong (>70% ionization; many ions in soln) and weak (<5%; few dissolved ions) electrolytes. –KF(aq)  K + (aq) F - (aq) ~ 100% ionization –AgF(aq)  Ag + (aq) F - (aq) ~ 0% ionization

AQUEOUS SOLUTIONS (3) Fig 4.4 shows relationship between electrolyte strength and light bulb current. Water can also dissolve nonionic cmps, especially those that are polar. (ethanol) Finally, many nonpolar molecules dissolve in water but do not produce ions in water; these are nonelectrolytes (sucrose, pure water).

STRONG ELECTROLYTES Three classes of strong electrolytes (~100% solubility in water) –soluble salts (T4.1) –strong acids (HCl, HBr, HI, H 2 SO 4, HNO 3, HClO 4 ); in general, acids produce H + (aq) and anion in water: HBr(aq)  H + (aq) + Br - (aq) (Arrhenius definition) –strong bases (M 1A OH, M 2A (OH) 2 for M 2A = Ca, Ba, Sr); in general, bases produce OH - (aq) and cation in water: KOH(aq)  K + (aq) + OH - (aq) (Arrhenius)

WEAK ELECTROLYTES Three classes of weak electrolytes (< 5% solubility) –insoluble salts (T4.1) –weak acids (acids other than those listed as strong). When weak acids are dissolved in water, few H + (aq) are produced. HF(aq)  H + (aq) + F - (aq) –weak bases (bases other than those listed as strong) When weak acids are dissolved in water, few OH - (aq) are produced. Fe(OH) 2 (aq)  Fe 2+ (aq) + 2OH - (aq)

QUANTIFYING SOLUTION COMPOSITION (MOLARITY, M) Concentration: Measure of quantity of solute in solvent –Molarity = M = #mol solute per l liter soln # mol solute = molarity * volume soln (L) = M * V # mol ion in a soln Dilution of concentrated (c, stock) soln to make dilute (d) soln: M c * V c = M d * V d

Figure 4.12a-c A Measuring Pipet is Used to Add Acetic Solution to a Volumetric Flask

SOLUTION STOIOCHIOMETRY Stoichiometric calculations for reactions taking place in aqueous solutions require –Balanced chem eqn Amount of chemicals present in rxn V A, M A  [#mol A  #mol B]  V B if M A and M B are known –[ * ] above designates basic stoich conversion from Chapter 3