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
(No Transcript)