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Title: When You Come In Please Pick Up


1
When You Come In Please Pick Up
  • Initial Soda Ash Questions worksheet

2
Percentage CompositionIsotopes, Empirical
Molecular Formulas
  • Edward A. Mottel Jeffrey E. Froyd
  • Department of Chemistry and Integrated,
    First-Year Curriculum in Science, Engineering and
    Mathematics

3
Atomic Composition
  • Protons, neutrons and electrons
  • Ions, cations and anions
  • Isotopes
  • Resources
  • Zumdahl Chapter 2.1-2.4, 3.1-3.5

4
Isotopes of Silver
  • Silver has two common isotopes
  • silver-107 and silver-109
  • Silver-107 has 47 protons and 60 neutrons

Why are these atoms considered to be isotopes of
each other?
What is the same and different about each isotope?
5
The element silver (Ag) has two naturally
occurring isotopes, 107 and 109. Its average
atomic mass is 107.868. Calculate the mass of
the heavier isotope
106.905
51.82
6
The element silver (Ag) has two naturally
occurring isotopes, 107 and 109. Its average
atomic mass is 107.868. Calculate the mass of
the heavier isotope
106.905
51.82
  • (mass 107Ag)( 107Ag)
  • (mass 109Ag)( 109Ag) avg. atomic mass

7
Solve Equation
  • soln solve((106.9050.5182) m109Ag(1 -
    0.5182)) 107.868, m109Ag)
  • soln 108.9037547

8
Chemical Analysis andEmpirical Formulas
  • Percentage composition by mass of a compound
  • Determination of the empirical formula from
    percentage by mass information
  • Empirical versus molecular formulas

9
Percentage Composition
What is the percentage silver in silver nitrate?
  • Silver Nitrate AgNO3
  • Molar Mass 1(AW Ag) 1(AW N) 3(AW O)
  • ( Ag) 1(AW Ag)/(Molar Mass)
  • ( N) 1(AW N)/(Molar Mass)
  • ( O) 3(AW O)/(Molar Mass)

10
Empirical Formula
  • Empirical formula problems are the reverse of
    percentage composition problems.
  • A compound that contains only carbon, hydrogen
    and oxygen is 48.38 C and 8.12 H. What is the
    empirical formula of this compound?

11
Empirical Formula CnCHnHOnO
  • eqn1 mass nC12.01nO16.00nH1.008
  • eqn2 nC12.01/mass 0.4838
  • eqn3 nO16.00/mass (1 - 0.4838 - 0.0812)
  • eqn4 nH1.008/mass 0.0812
  • sln solve(eqn1, eqn2, eqn3, eqn4, mass, nH,
    nC, nO)
  • sln nO .6749108619 nC, mass 24.82430757
    nC, nH 1.999735887 nC, nC nC
  • (CH2O2/3)nC -----gt (C3H6O2) nU

12
Empirical vs. Molecular Formulas
  • Empirical Formula (C3H6O2) nU
  • Possible Molecular Formulas
  • C3H6O2 nU 1
  • C6H12O4 nU 2
  • C9H18O6 nU 3

What would be the molecular formula if the
approximate MW is 150 gmol-1?
13
Carbohydrates
  • Carbohydrates are compounds with the general
    formula Cm(H2O)n where m is typically 5 or
    greater and nltm.
  • Show that sucrose C12H22O11 is a carbohydrate.
  • Do all carbohydrates have the same percentage
    composition for each element?

14
Sodium Bicarbonate Thermal Decomposition
  • Sodium bicarbonate decomposes when heated to form
    solid sodium carbonate, water vapor and carbon
    dioxide.
  • If 2.00 grams of sodium bicarbonate is heated and
    completely decomposed, what will be the mass of
    the remaining solid?
  • In your group decide on the sequence of steps
    needed to solve this problem.

15
Sodium Bicarbonate Thermal Decomposition
  • Process
  • Balance equation
  • Identify a pathway to go from mass of reactant to
    mass of product.
  • Calculate the answer.
  • Check your answer -- does it seem reasonable?

16
Sodium Bicarbonate Thermal Decomposition
  • Sodium bicarbonate decomposes when heated to form
    solid sodium carbonate, water vapor and carbon
    dioxide.
  • If 2.00 grams of sodium bicarbonate is heated and
    is 60 decomposed, what will be the mass of the
    remaining solid?
  • In your group decide on the sequence of steps
    needed to solve this problem.

17
Sodium Bicarbonate Thermal Decomposition
0.76 g
2.00 g
0.80 g
1.56 g
18
Sodium Bicarbonate Thermal Decomposition
  • A little harder problem
  • If 2.00 gram sample of sodium bicarbonate is
    heated and has a mass of 1.56 grams after
    heating, what is the percentage converted
    (percentage yield)?
  • Hint How many moles of CO2 and H2O are produced?
    How many moles of NaHCO3 have decomposed?

19
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