Matter and Measurement

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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
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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

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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)

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Practice Problem 4-1 Answer

• 2.00 g Ag2CrO4

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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)

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Practice Problem 4-2 Answer

• A) 2.89 g PbS
• (theoretical)
• B) Actually make 2.64g (actual)
• What is your percent yield?

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Practice Problem 4-2B Answer

• B) Actually make 2.64g
• What is your percent yield?
• yield 100
• yield 100
• .9135 x 100 91.349

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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?

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Practice Problem 4-3 Answers

• 2.69 g CO2

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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)

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Practice Problem 4-4 Answer

• 95.6

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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)

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Practice Problem 4-5 Answer

• 94.49

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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

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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

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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?

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p.162b
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Next Lesson

• Chapter 5
• Homework due

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Balancing Equations

• ____C3H8(g) _____ O2(g)
  ----gt _____CO2(g) _____ H2O(g)

____B4H10(g) _____ O2(g)
----gt ___ B2O3(g) _____ H2O(g)
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