AP Chapter 3 Chemical Reactions and Solution Stoichiometry (Solutions of cadmium nitrate and sodium sulfide are mixed)

Solutions – homogeneous mixtures. All solutions are composed of a solute(s) and a solvent. Solute – the substance present in lesser amount in a solution.(dissolvee) Solvent – the substance present in greater amount in a solution.(dissolver) Universal Solvent – Water, water dissolves a large number of substances due to it’s polarity. Water is very polar, due to it’s two unshared pairs of electrons.

Solubility of substances Polar substances dissolve polar substances. Nonpolar substances dissolve nonpolar substances. Polar substances do NOT dissolve nonpolar substances. “LIKES dissolve LIKES”

Structure of water

hydration The polarity of water can break up some compounds, called hydration. Hydration – the splitting of an ionic compound into cations and anions by the polar ends of a water molecule.

Polar Water Molecules Interact with the Positive and Negative Ions of a Salt

An Ionic Compound, CuCl2, in Water CCR, page 149

Polar Bonds can cause polar covalent(molecular) compounds to dissolve in water.

When ionic compounds dissolve in water, they ionize: Ionic compound  cation + anion MgCl2 (s)  NaOH (s)  NH4OH (s)  NaNO3 (s)  H2SO4 (l)  C6H12O6 (s) 

Aqueous Solutions How do we know ions are present in aqueous solutions? The solutions conduct electricity! They are called ELECTROLYTES HCl, MgCl2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions.

Aqueous Solutions HCl, MgCl2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions.

Aqueous Solutions CH3CO2H(aq) ---> CH3CO2-(aq) + H+(aq) Acetic acid ionizes only to a small extent, so it is a weak electrolyte. CH3CO2H(aq) ---> CH3CO2-(aq) + H+(aq)

molecular substances solubility increases with more polar side groups, usually hydroxyl (alcohol) groups. (See Dry Erase Board)

Electrolytes – substances which form ions in water. Strong electrolytes – complete ionization Weak electrolytes - partial ionization Nonelectrolytes – polar molecular solutes (zero ionization)

Types of Strong Electrolytes 1) Strong Acids(HX  H+ + X-) 2) Strong Bases(MOH  M+ + OH-) 3) Soluble Salts(MN  M+ + N-) X = conjugate base M = metal N = nonmetal(s)

Simple Rules for Solubility 1. Most alkali (group 1A) salts and NH4+ are soluble. 2. Most nitrate (NO3), acetate (C2H3O2-), clorate/perchlorate (ClO3-/ClO4-)salts are soluble. Most Cl, Br, and I salts are soluble . (NOT Ag+, Pb2+, Hg22+) Most sulfate salts are soluble (NOT BaSO4, PbSO4, HgSO4, CaSO4, Ag2SO4) 5. Most OH salts are NOT, soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble) 6. Most S2, CO32, CrO42, PO43 salts are only slightly soluble.

Pop-quiz Write each formula, then determine if it is soluble or insoluble in water: Substance Formula Soluble/insoluble Silver nitrate