CHAPTER 4 AP CHEMISTRY PRECIPITATION PROBLEMS Water Highly polar Ionic and polar compounds are attracted to the positive and/or negative ends of the water molecule. This is called HYDRATION (a hydration reaction is something different) When a precipitate is formed there is a zero net charge Solubility rules (handout) What happens when a ionic compound dissolves in water? They break up into their ion form What are spectator ions? Ions that do not participate in the reaction You must show that atoms and charges are balanced ELECTROYTES Solute - substance Solvent - water, what you put solute in Electrolytes- conduct electricity Strong - strong acids and bases, soluble salts Weak - weak acids and bases, insoluble or slightly soluble salts Nonelectroytes - molecules, nonpolar covalent compounds ARRHENIUS Ions are responsible for conducting electricity Down played convictions to get PhD then crusaded to get theory accepted Received Nobel prize 1903 OXIDATION-REDUCTION REACTIONS An oxidation-reduction reaction involves transfer of electrons Addition of O2 or H2 often occur LEO goes GER Oxidized or oxidation Species that lose electrons oxidation number goes up Reduced or reduction Species that gain electrons or oxidation number reduced Oxidizing agent What causes oxidation Reducing agent What causes reduction OXIDATION NUMBER RULES Elements found in nature is zero Cu, O2 Monoatomic ions same as charge Cl-, Mg2+ Fluorine always 1Oxygen 2 Except with fluorine 2+ Peroxide 1-, H2O2 Superoxide ½ -, KO2 Hydrogen 1+ With group one elements then a hyride 1Sum of oxidation numbers of a neutral compound is zero The most electronegative element number is the same as the ion charge Sum of oxidation numbers of a polyatomic ion is same as its charge REDOX The concept of oxidation numbers explain oxidation and reduction Oxidation: increase in oxidation number (lose electrons) Reduction: decreases in oxidation number (gain electrons) Balancing redox equations The half-equation method Split the equation into two half-reactions One for reduction and the other for oxidation Balance one of the half-reactions; balance atom other than O or H first, next use water to balance oxygen, then add hydrogen ions to balance the hydrogen, add electrons to balance charge Balance other half-reaction Combine the two in such away as to eliminate all the electrons MOLARITTY Number of moles of solute per liter of solution M = number of mol/L Symbol [ ] means molar concentration Moles of solute after dilution = moles of solute before dilution M1V1 = M2V2 TITRATION A volumetric analysis involving titration, where a measured volume of a known concentration of an acid or base is required to find the exact concentration (the volume must be known) of an unknown base or acid Equivalent point Where exact stoichometry amounts of each reactant are present. (same number of H+ and OH- ) NO EXCESSES End point Where the indicator changes color. Immediately stop adding titrate.