Chemistry Notes Chapter 4 The Three Major Classes of Chemical Reactions Dissolved in water broken up into individual elements molecs Electrolyte a substance that conducts a current when dissolved in water Dissolving Solvated Determine moles of ions in products by looking at formula and knowing number of moles of formula we have Soluble ionic compounds completely dissociate in solutions Using formula to find of moles of ions in solution POLYATOMIC IONS Find the formula Find of moles given mass or formulas Multiply by mole ratios Depictions to understand solution rxns Count number of positive and negative ions Match up with reactant and its element s molecule s charges Water molecules have a north and South Pole Very polar Pos and Neg Oxygen is negative two hydrogens are positive Water can t break strong high ionic charge bonds Polar due to distribution of electrons and shape Covalent Compounds in water are nonelectrolytes b c they do not form ions Acids are covalent but react strongly with h2o to produce ions Finding Molarity Write equation Use mole ratio H3O H2O H2O H7O3 Example of proton in water Hydronium ion Writing equations for Aqueous Ionic Rxns If solutions of two ionic compounds are mixed a rxn occurs only if ions leave solution precipitate make water gas formed Many possible products can form but all are water soluble no reaction occurs Three major types of aqueous ionic rxns 1 Precipitation 2 Neutralization 3 Rxns form gaseous product Precipitation Rxns Solution rxns 2 ionic compounds form precipitate Molecular equation shows reactants and products as dissociated compounds Total Ionic Equation take compound that forms electrolytes and dissociate them shows all the soluble ionic substances dissociated into ions What really happens Only the ions that react to form precipitate matter the ions that don t undergo change spectator ions not involved Net Ionic Equation ridding of spectator ions When does a precipitate form Rules Solubility Rules Predicting Precipitate equations Cations and anions change partners Look at solubility rules for each product Insoluble Precipitation rxn occurs Molecular equation write out all completely Precipitates denoted by s Total ionic break down by ions any nonprecipitate are spectator ions Net Ionic mark out all spectator ions Acid Base Rxns Neutralization Rxns Acids produce H ions when dissolved in H2O Bases produce OH in water Acids and bases grouped by strength strong weak Strong dissociates completely into H and element molecule Most weak remain fully in tact Table 4 2 Strong bases contain either OH or O2 ions Strong Acid Strong Base Salt H2O total ionic equation remember the H and OH s net ionic is H OH H2O Acid Base Titrations Neutralization rxn done quantitatively Known vol of acid base slowly added End pt occurs when the color just stays At equivalence pt H moles OH mol Can then calculate concentration of the acid Calculating unknown concentration Balance equation need mole ratio coefficient Take vol of base L then find moles of base Convert to moles of acid Calculate molarity of acid MV MV Redox Rxns Elements change charge by picking up or losing electrons MUST BALANCE ELECTRONS Oxidation is Loss of e Reduction is Gain of e OIL RIG Do half rxns go through it oxidation and reduction taking in electrons to consideration Oxidizing Agent is Reduced Reducing Agent is oxidized Oxidation increase in oxidation number Need to be able to pick out which is reduced oxidized Assignment of oxidation number Table 4 3 Rules Keep track of electrons and where they go Sum of ON value for the atoms in a compound equals ZERO Sum polyatomic ions ion s normal charge Elemental form 0 Monatomic Ion Ionic charge 1atom IF not a special case it is a simple element O N charge Rules Ex SO3 Each Oxygen according to rule each O 2 so ON of O is a total of 6 THEREFORE O N of S MUST BE 6 b c sum all compounds O N 0 Selecting Oxidizing and Reducing agents Assign oxidation numbers which increases which decreases then deduct answer Use rules first If equation is like H2SO4 each element s charge is counted for each atom Balancing Redox Equations Number of e lost by the oxidized reactant must equal the number of e gained by the reduced reactant page 163 5 step method Assign O N see whether or not its redox Balance like normal for atoms first Theeen compare number of electrons lost and gained Then use elements on the other side of the equation The electrons gained and lost have to come from somewhere ALWAYS CHECK BY assigning O N Reaction Types Combination Synthesis Decomposition Single Displacement double displacement metathesis Combustion sub category of redox Combo X Y XY 2 nonmetals binary covalent compound Metal oxide nonmetal oxide ionic compound oxoanion Decomposition Z X Y Sometimes O2 and H2O are released Displacement Single X YZ XZ Y Double Metathesis WX YZ WZ YX products Atom or ion in a compound is displaced by an atom or ion of another element Single displacement some metals can displace hydrogen from water or acids