Chapter 4: Aqueous Rxns and Solution Stoichiometry Recommended Text Problems 1, 3, 7, 13, 19, 21, 25, 31, 37, 39ac, 41b, 45, 49, 51, 55abe, 59, 63, 65b, 71, 75, 79abc, 81, 85, 90, 92, 103, 107 Schedule 04 27 Chapter 4: Aqueous Reactions and Solution Stoichiometry 5. Solubility Rules, Types of Reactions and N.I. Equations Data Collection 04 29 Chapter 4: Aqueous Reactions and Solution Stoichiometry 5. Solubility Rules, Types of Reactions and N.I. Equations Data Analysis 05 04 Chapter 4: Aqueous Reactions and Solution Stoichiometry 6. Standardization of a NaOH Solution 05 06 Chapter 5: Thermochemistry 7. Molar Mass of an Unknown Solid Acid (LQ02) 4 5 Solutions Definition: Components The solvent The solutes Dissociation Definition Animation Electrolytes An electrolyte is a substances that A strong electrolyte A weak electrolyte Strong Electrolytes Strong acids Strong bases Hydroxide Soluble ionic salts Electrolytes A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so. Electrolytes and Nonelectrolytes Chemical Reactions After mixing chemicals together, how do you know reactions occurred Precipitation Reactions Solution Chemistry How can we predict what reactions occur in a reaction mixture? Equations The molecular equation The (total, complete) ionic equation The net ionic equation, Writing Net Ionic Equations 1. 2. 3. 4. Write a balanced molecular equation. Dissociate all strong electrolytes. Cross out anything that remains unchanged from the left side to the right side of the equation. Write the net ionic equation with the species that remain. CaCO3(s) + HCl → ? Molecular Equation: Total Ionic Equation: Net Ionic Equation: Writing Net Ionic Equations K3PO4(aq) + 3HNO3(aq) → ? KNO3(aq) + HCl(aq) → ? Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose.” It appears the ions in the reactant compounds exchange, or transpose, ions. Equations AgNO3 (aq) + KCl (aq) ⎯→ Acid-Base Reactions Characteristics Acid Base Arrhenius Concept of Acids and Bases Acid Base Arrhenius Concept of Acids and Bases Strong acid A substance There are only seven strong acids: Arrhenius Concept of Acids and Bases Strong base A substance The strong bases are the soluble metal salts of hydroxide ion: Arrhenius Concept of Acids and Bases Most other acids and bases are weak. They are An example is acetic acid, HC2H3O2. Ammonium hydroxide, NH4OH, is a weak base. Arrhenius Concept of Acids and Bases Strong base A substance ionizes completely in aqueous solution to give OH-(aq) and a cation. The strong bases are the soluble metal salts of hydroxide ion: Alkali metals Calcium Strontium Barium Arrhenius Concept of Acids and Bases Polyprotic Acid Example: Arrhenius Concept of Acids and Bases Ammonia, NH3?? Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and water. CH3COOH + NaOH (aq) ⎯→CH3COONa (aq) (aq) + H2O (l) Neutralization Reactions Net ionic reaction Strong acid + Strong base Strong acid + Weak base Weak acid + Strong base Weak acid + Weak base Brønsted-Lowry Concept of Acids and Bases Acid Base Brønsted-Lowry Concept of Acids and Bases Conjugate acid-base pair Example: Gas-Forming Reactions Some metathesis reactions do not give the product expected. When a the products are a salt, carbon dioxide, and water. When a The products are a salt, sulfur dioxide, and water. Oxidation-Reduction Reactions An oxidation occurs A reduction occurs One cannot occur without the other. Oxidation Numbers Elements in their elemental form have an oxidation number of 0. The oxidation number of a monatomic ion is the same as its charge. The sum of the oxidation numbers in a neutral compound is 0. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion. Oxidation Numbers Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Displacement Reactions In displacement reactions, For example: silver ions oxidize copper metal. Cu (s) + 2 Ag+ (aq) ⎯→ Cu2+ (aq) + 2 Ag (s) The reverse reaction, however, does not occur. Cu2+ (aq) + 2 Ag (s) ⎯→ Cu (s) + 2 Ag+ (aq) x Activity Series Molarity Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. Molarity is one way to measure the concentration of a solution. Example Calculate the molarity of a solution made by dissolving 23.4 g of sodium sulfate (Na2SO4) in enough water to form 125 mL of solution. Practice Calculate the molarity of a solution made by dissolving 5.00 g of glucose (C6H12O6) in sufficient water to form exactly 100 mL of solution. Example What are the molar concentrations of each of the ions present in a 0.025 M aqueous solution of calcium nitrate? Practice (a) How many grams of Na2SO4 are there in 15 mL of 0.50 M Na2SO4? (b) How many milliliters of 0.50 M Na2SO4 solution are needed to provide 0.038 mol of this salt? To Prepare a Solution with Known Concentration To prepare a solution of a known molarity, Dilution Example How many milliliters of 3.0 M H2SO4 are needed to make 450 mL of 0.10 M H2SO4? Practice (a) What volume of 2.50 M lead(II) nitrate solution contains 0.0500 mol of Pb2+? (b) How many milliliters of 5.0 M K2Cr2O7 solution must be diluted to prepare 250 mL of 0.10 M solution? (c) If 10.0 mL of a 10.0 M stock solution of NaOH is diluted to 250 mL, what is the concentration of the resulting stock solution? Using Molarities in Stoichiometric Calculations Example How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of 0.100 M HNO3? Practice a) How many grams of NaOH are needed to neutralize 20.0 mL of 0.150 M H2SO4 solution? b) How many liters of 0.500 M HCl(aq) are needed to react completely with 0.100 mol of Pb(NO3)2(aq), forming a precipitate of PbCl2(s)? Titration Titration Example How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of 0.100 M HNO3? Practice a) How many grams of NaOH are needed to neutralize 20.0 mL of 0.150 M H2SO4 solution? b) How many liters of 0.500 M HCl(aq) are needed to react completely with 0.100 mol of Pb(NO3)2(aq), forming a precipitate of PbCl2(s)? Vocabulary/Terminology Electrolyte Arrhenius Acids/Bases Brønsted-Lowry Acids and Bases Metathesis (Exchange) Reactions Double replacement reaction Displacement Reactions Neutralization Reactions Oxidation/ Reduction Dilution Titration Standardization