CHEM 161 Exam 2 Study Guide F2014 page 1 of 3 CHEM 161: Exam 2 Study Guide Chapter 3: Stoichiometry Stoichiometry: Use mole‐to‐mole ratios to relate amounts of reactants and/or products Limiting Reagent Problems – Calculate the mass, volume, or concentration of product that can be made from each of given amount of reactants and using chemical equation. – Calculate the amount of reactant in excess that remains after the reaction. – Recognize that you need to calculate moles—not mass!—to determine the molarity of a product or reactant in excess. Yields of Reactions – theoretical yield: amount of product predicted using the balanced equation when limiting reagent is used up (can be calculated) – actual yield: amount of product one actually gets (generally given in the problem) Percent yield = – Given the percent yield for a reaction, determine the amount of reactant required for a given amount of product Chapter 4: Types of Chemical Reactions Aqueous Solutions: liquid or solid solute in H2O – solution: mixture of 2 or more substances – solute: substance present in smaller amount – solvent: substance present in larger amount Precipitation Reactions – precipitate (ppt): solid forming from 2 solutions – Use Solubility Rules to determine if ppt forms – Predict products of a reaction given reactants and Solubility Rules. – Predict all of the precipitates that would form when various ionic compounds are dissolved in the same beaker. Acid‐Base Neutralization Reactions – Know Arrhenius and Bronsted‐Lowry (B‐L) definitions for acids and bases – Identify B‐L acid/base in a chemical equation – Predict products for acid‐base reactions – HX + MOH water + salt – HX + MHCO3 water + CO2 + salt – HX + MCO3 water + CO2 + salt Oxidation‐Reduction (Redox) Reac tions – Determine oxidation #’s for atoms in equations. – Use oxidation # to determine the reactant oxidized (reducing agent) and reactant reduced (oxidizing agent) – Determine the # of electrons gained or lost. Oxidation‐Reduction (Redox) Reac tions – Predict products given reactants for: – Combination reaction – metal + nonmetal ionic compound (s) – Single‐replacement reactions – Activity Series, list of Active Metals, and Solubility Rules, where reactants are: – solid metal + metal solution – solid metal + acid – solid metal + H2O(l) – Combustion reaction – CxHy + O2 CO2 (g) + H2O (g) – CxHyOz + O2 CO2 (g) + H2O (g) – Balance and identify Decomposition reactions Strong, Weak and Non‐Electrolytes – strong electrolyte: breaks up completely many ions present to conduct electricity – e.g. strong acids & bases, aqueous salts – weak electrolyte: breaks up to small degree only few ions present to conduct electricity – e.g. weak acids & bases, insoluble salts – nonelectrolyte: a molecular compound that forms molecules in water no ions does not conduct electricity CHEM 161 Exam 2 Study Guide F2014 page 2 of 3 Chapter 4: Types of Chemical Reactions (Continued) Acids and Bases as electrolytes – Know strong acids and strong bases in notes! – All other acids and bases are weak – Know how H2SO4 dissociates in water. Chemical Equations and (Net) Ionic Equations – Chemical Equation: compounds shown as whole – Complete/Total Ionic Equation: – shows strong electrolytes as separated ions – Spectator Ions: unchanged in chemical reaction – Net Ionic Equation: Shows what substances change in a chemical reaction Guidelines for writing Net Ionic Equations: 1. Complete and balance molecular/chem equation 2. Leave solids, liquids, gases, weak electrolytes as compounds; break up strong electrolytes 3. Cancel spectator ions 4. Simplify coefficients if possible 5. If all reactants and products cancel (all spectator ions) NR Experimental Observations of Double‐Replacement Precipitation and Acid‐Base Neutralization Reactions – Given a table of experimental results similar to the “Double Replacement/Metathesis” experiment, determine the cation and anion that must be present in a solution of an unknown soluble ionic compound Oxidation‐Reduction (Redox) Reac tions – Be able to determine oxidation numbers for all the atoms/elements in a chemical equation. – Use oxidation numbers to determine which reactant was oxidized (reducing agent) and which reactant was reduced (oxidizing agent) – Determine the # of electrons gained or lost. Balance redox reactions in acidic and basic solution using the half‐reaction method. – Balance atoms and electrons transferred, then balance O atoms using H2O and H atoms using H+ ions (in acidic solution) – In basic solution, neutralize H+ ions with OH‐ ions – Cancel H+, OH‐, and H2O on both sides of the equation and simplify coefficients Molarity, Solution Stoichiometry, and Volumetric Analysis Calculations – Use molarity and volume to solve for moles. – Use balanced chemical equation to determine mole‐to‐mole ratios needed to solve problems. – Calculate the molarity of a compound or an ion in a solution. – Use the dilution equation: M1 V1 = M2 V2 for dilution problems Acid‐Base Titrations – Know the definitions for standard solution, acid‐base indicators, titration, and endpoint. – Solve problems using titration data. Mass Percent Concentraton: M/M%=mass of solute×100%mass of solution – Solve for or use mass percent concentration in various calculations. – Solve for mass percent concentration for mixtures (e.g. % CaCO3 in limestone) – Solve a variety of problems combining molarity, mass percent concentration, and topics covered from previous chapters. Chapter 6: Properties of Gases - Know the physical properties of gases. - Know the elements and common compounds that exist as gases at 25˚C and 1 atm pressure. - Know the definitions for the following: vacuum, gas pressure, atmospheric pressure, barometer, and manometer - Know how a manometer works, and be able to solve for gas pressure. CHEM 161 Exam 2 Study Guide F2014 page 3 of 3 Chapter 6: Properties of Gases Gas pressure and Atmospheric pressure – Standard atmospheric pressure: 760 torr at 0˚C at sea level – Be able to convert between units of
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