Chapter 18 Ions in Aqueous Solutions

18.1 Ionic Compounds in Aqueous Solution Theory of Ionization 1.Michael Faraday a. Atoms are associated with electrical powers b. Coined the terms electrolyte and nonelectrolyte c. Mistakenly thought ions formed at the electrodes during electrolysis

2.Arrhenius a. Believed ions were produced by ionization of molecules in aqueous solution b. Ions were electrically charged c. Strong electrolytes completely dissociate d. Weak electrolytes do not dissociate

Dissolving Ionic Compounds 1.hydration: solution process with water as the solvent 2.Each ion is surrounded by water molecules 3.Hydrated ions become uniformly distributed in the solution 4.Number of water molecules surrounding each hydrated ion depends upon the size and charge of the ion

A dynamic equilibrium is established, Na + + n H 2 O (l)  [Na(H 2 O) n ] + Where n is the number of water molecules

5. hydrates a. Crystals retain the water b. CuSO 4  5 H 2 O (copper (II) sulfate pentahydrate) 6. Heat of solution for ionic compounds a. the overall result of the energy changes occurring during ionization

b. heat of hydration 1. energy released when ions become surrounded by water molecules 2. more energy is usually released with smaller ions 3. more energy is released with ions with higher charges

c. Ex. Ion Radius Heat of hydration Li + 68 pm -523 kJ/mole Mg pm kJ/mole d. The release or absorption of energy depends upon the energy needed to: 1. to separate the ions in the crystal from each other 2. to hydrate the ions

Exothermic solution process

Endothermic solution process

7. Dissociation a. The separation of ions that occur when an ionic compound dissolves b. Ex. 1. NaCl (s)  2. CaCl 2 (s) 

Solubility Equilibria 1.Very slightly soluble ionic compounds a. An equilibrium is established between the solid compound and its ions in solution

b.

2. Precipitation reactions a. Double-replacement reactions b. Use the solubility rules c. Ex. KCl (aq) + AgNO 3 (aq) 

3. Net ionic equations a. Shows all the dissociated ions b. Leaves the insoluble compound (precipitate) c. Ex. KCl (aq) + AgNO 3 (aq) 

18.2 Molecular Electrolytes 1. Polar covalent usually conduct electricity 2. The opposite dipoles (δ + or δ - ) attract each other 3. A-B  A + + :B - 4. the formation of ions is called ionization

5. Ex. HCl   18.3 Properties of Electrolyte Solutions 1. Colligative properties of Electrolyte solutions a. Freezing-point depression (K f ) 1. water’s K f = °C/m 2. ΔT f = K f m( # of ions) where ΔT f = temp change K f = freezing-point constant m = molality

3. Ex. What is the expected change in the freezing point of water in a solution of 62.5 g of barium nitrate in 1.00 kg of water? Ba(NO 3 ) 2  Ba NO 3 - ΔT f = K f m (# of ions) = °C/m 62.5g of Ba(NO 3 ) 2 1 mole Ba(NO 3 ) 2 = 1.00 kg H 2 O