CHAPTER 4 Chemical Equations and Stoichiometry

CHAPTER 4 Chemical Equations and Stoichiometry Chapter 4 “Quiz” points - complete all assigned homework problems from the chapter - submit on Monday, Feb 12 - problems selected randomly for grading Chem 105 Chpt 4 Lsn 9

Road Map • Where we were • Balanced equations from neutral formulas, containing ionic equations, and one with polyatomic ions (Table 3.1 available on test) • Relationships: when comparing different compounds, must always go through a MOLE comparison • Limiting reactant (reagent) • Where we are going • Percent yield • Chemical equations and chemical analysis Chem 105 Chpt 4 Lsn 9

Practice Problem 4-1 • When aqueous silver nitrate and sodium chromate solutions are mixed, a reaction occurs that forms solid silver chromate and a solution of sodium nitrate. If 257.8 mL of a 0.0468 M solution of silver nitrate is added to 156.00 ml of a 0.095 M solution of sodium chromate, what mass of solid silver chromate (M = 331.8 g/mol) will be formed? 2 AgNO3(aq) + Na2CrO4(aq) → Ag2CrO4(s) + 2 NaNO3(aq) Chem 105 Chpt 4 Lsn 9

Practice Problem 4-1 Answer • 2.00 g Ag2CrO4 Chem 105 Chpt 4 Lsn 9

Practice Problem 4-2 • A) If 257.8 mL of a 0.0468 M solution of lead(II) nitrate is added to 156.00 mL of a 0.095 M solution of sodium sulfide, what mass of solid lead(II) sulfide will be formed? Pb(NO3)2(aq) + Na2S(aq) → PbS(s) +2 NaNO3(aq) Chem 105 Chpt 4 Lsn 9

Practice Problem 4-2 Answer • A) 2.89 g PbS (theoretical) • B) Actually make 2.64g (actual) • What is your percent yield? Chem 105 Chpt 4 Lsn 9

Practice Problem 4-2B Answer • B) Actually make 2.64g What is your percent yield? % yield = × 100 % yield = × 100 = .9135 x 100 = 91.349 % Chem 105 Chpt 4 Lsn 9

Practice Problem 4-3 • Potassium permanganate reacts with oxalic acid in aqueous sulfuric acid according to the following equation: 2 KMnO4 + 5 H2C2O4 + 3 H2SO4→ 2 MnSO4 + 10 CO2 + 8 H2O + K2SO4 If you start with 3.225 g of H2C2O4 and 75.0 mL of 0.250 M of KMnO4 and the percent yield is 85.3 %, what is the actual yield of CO2? Chem 105 Chpt 4 Lsn 9

Practice Problem 4-3 Answers • 2.69 g CO2 Chem 105 Chpt 4 Lsn 9

Practice Problem 4-4 • Given the chemical reaction between iron and water to form the iron oxide, Fe3O4 and hydrogen gas given below. If 4.55 g of iron is reacted with sufficient water to react all of the iron to form rust, what is the percent yield if only 6.02 g of the oxide are formed? 3 Fe(s) + 4 H2O(l) → Fe3O4(s) + 4 H2(g) Chem 105 Chpt 4 Lsn 9

Practice Problem 4-4 Answer • 95.6 % Chem 105 Chpt 4 Lsn 9

Practice Problem 4-5 • Ammonia is produced by the Haber process using nitrogen and hydrogen gas. If 85.90 g of nitrogen are reacted with 21.66 g hydrogen and the reaction yielded 98.67 g of ammonia. What was the percent yield of the reaction? N2(g) + 3 H2(g) → 2 NH3(g) Chem 105 Chpt 4 Lsn 9

Practice Problem 4-5 Answer • 94.49 % Chem 105 Chpt 4 Lsn 9

Chemical Analysis • 72. What mass of lime, CaO, can be obtained by heating 125 kg of limestone that is 95% by mass CaCO3? CaCO3 (s)  CaO (s) + CO2 (g) • 6.65 X 104 g CaO Chem 105 Chpt 4 Lsn 9

Chemical Equation • A dry-cleaning solvent (M = 146.99 g/mol) that contains C, H, and Cl is suspected to be a cancer-causing agent. When a 0.250 g sample was studied by combustion analysis, 0.451 g of CO2 and 0.0617 g of H2O formed. Calculate the molecular formula. • Empirical C3H2Cl • Molecular C6H4Cl2 Chem 105 Chpt 4 Lsn 9

Are you up to the challenge? • Iodine is made by the reaction 2 NaIO3 (aq) + 5 NaHSO3 (aq)  3 NaHSO4 (aq) + 2 Na2SO4 (aq) + H2O (l) + I2 • Name the two reactants • If you wish to prepare 1.00 kg of I2, what mass of NaIO3 is required? • What mass of NaHSO3? Chem 105 Chpt 4 Lsn 9

Chem 105 Chpt 4 Lsn 9 p.162b

Next Lesson • Chapter 5 • Homework due Chem 105 Chpt 4 Lsn 9

Balancing Equations ____C3H8(g) + _____ O2(g) ----> _____CO2(g) + _____ H2O(g) ____B4H10(g) + _____ O2(g) ----> ___ B2O3(g) + _____ H2O(g) Chem 105 Chpt 4 Lsn 9

Chem 105 Chpt 4 Lsn 9

CHAPTER 4 Chemical Equations and Stoichiometry