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

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

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

4. 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)

5. 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

6. 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

7. 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–)

8. 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)

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

10. 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