Aqueous Solutions; Solubility Rules AP Chem General Properties - - PowerPoint PPT Presentation
Aqueous Solutions; Solubility Rules AP Chem General Properties Recall: Homogeneous mixture of 2 or more pure substances Aqueous Solutions of interest because water is polar, can dissolve many polar and ionic substances Hydration is process in
Recall: Homogeneous mixture of 2 or more pure substances Aqueous Solutions of interest because water is polar, can dissolve many polar and ionic substances Hydration is process in which H2O molecules surround an ion or molecule to dissolve it.
Ions undergo hydration when formed Each ion surrounded by H2O molecules with oppositely charged end of dipole oriented toward it Stabilizes ions & prevents recombination
Soluble ionic compounds, dissociate when dissolved: AxBy (s) xAn+(aq) + yBm–(aq), where x(n+) + y(m–) = 0 e.g. Na3PO4(s) 3Na+(aq) + PO43–(aq) Ions in solution provide mobile charges to conduct electricity Stronger solutions, higher solubility give higher conductivity Ionic compounds also conduct when molten (mobile charges) Strong Acids & Bases dissociate/ionize completely, so are strong electrolytes e.g. HCl(g) H+ (aq) + Cl– (aq) Weak Acids & Bases partially ionize, so are weak electrolytes e.g. HF (aq) ⇌ H+ (aq) + F– (aq) Molecular substances (e.g. sugar) do not ionize, no conductivity—Nonelectrolytes
H2O
⎯ → ⎯ ⎯
H2O
⎯ → ⎯ ⎯
H2O
⎯ → ⎯ ⎯
All soluble ionics are strong electrolytes (including ionic bases–e.g. NaOH, KOH) All molecular substances (covalent compounds) are non- electrolytes except for acids and NH3, R2NH All strong acids are strong electrolytes HCl, HBr, HI, HNO3, H2SO4, HClO4 **MEMORIZE! Dissociate completely in water All other acids are weak electrolytes Some common weak acids: HF, HNO2, H3PO4, CH3COOH (acetic acid) Dissociate only slightly in water Ammonia (NH3) is a weak electrolyte (weak base) MEMORIZE
When two solutions are brought together, an insoluble combination of cation-anion may form (remember double replacement!) Insoluble compound precipitates from solution. Predict product based on solubility rules
Always soluble: alkali metal ions (Li+, Na+, K+, Rb+, Cs+), NH4+, NO3–, ClO3–, ClO4–, CH3COO– (C2H3O2–) Generally soluble: Cl–, Br–, I– Soluble except Ag+, Pb2+,Hg22+ (CuI2 insol.) F – Soluble except Ca2+, Sr2+, Ba2+, Pb2+ , Mg2+ SO42– Soluble except Ca2+, Sr2+, Ba2+, Pb2+, Hg22+ Generally insoluble: O2–, OH– Insoluble except alkali metals and NH4+ Somewhat soluble Ca2+, Sr2+, Ba2+ CO32–, PO43–, S2–, SO32–, C2O42–, CrO42– Insoluble except alkali metals and NH4+
Exceptions have common trends: Ca, Ba, Sr often exceptions (i.e. SO42–, OH–) Ag+, Pb2+, Hg22+ always insoluble unless with always soluble anion Most anions always insoluble unless with always soluble cation Examples: Are the following compounds soluble or insoluble? K2SO4; AgNO3; AgCl, K2S, BaSO4, CaCO3 For AP exam, need to know Na+, K+, NO3– In double-replacement reactions, the there will always be