6/26/2015 When You Come In Please Pick Up  Initial Soda Ash Questions worksheet

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

Atomic Composition  Protons, neutrons and electrons  Ions, cations and anions  Isotopes Resources  Zumdahl: Chapter ,

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?

The element silver (Ag) has two naturally occurring isotopes, 107 and 109. Its average atomic mass is Calculate the mass of the heavier isotope Isotope Mass (amu) Percentage Ag % Ag

The element silver (Ag) has two naturally occurring isotopes, 107 and 109. Its average atomic mass is Calculate the mass of the heavier isotope (mass 107 Ag)*(% 107 Ag) + (mass 109 Ag)*(% 109 Ag) = avg. atomic mass Isotope Mass (amu) Percentage Ag % Ag

Solve Equation  soln := solve(( *0.5182) + m109Ag*( )) = , m109Ag); soln :=

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

Percentage Composition  Silver Nitrate: AgNO 3  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) What is the percentage silver in silver nitrate?

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?

Empirical Formula: C nC H nH O nO  eqn1 := mass = nC*12.01+nO*16.00+nH*1.008;  eqn2 := nC*12.01/mass = ;  eqn3 := nO*16.00/mass = ( );  eqn4 := nH*1.008/mass = ;  sln := solve({eqn1, eqn2, eqn3, eqn4}, {mass, nH, nC, nO});  sln := {nO = nC, mass = nC, nH = nC, nC = nC}  (CH 2 O 2/3 ) nC -----> (C 3 H 6 O 2 ) nU

Empirical vs. Molecular Formulas  Empirical Formula: (C 3 H 6 O 2 ) nU  Possible Molecular Formulas: C 3 H 6 O 2 nU = 1 C 6 H 12 O 4 nU = 2 C 9 H 18 O 6 nU = 3 What would be the molecular formula if the approximate MW is 150 g·mol -1 ?

Carbohydrates  Carbohydrates are compounds with the general formula C m (H 2 O) n where m is typically 5 or greater and n<=m. Show that sucrose C 12 H 22 O 11 is a carbohydrate. Do all carbohydrates have the same percentage composition for each element?

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.

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?

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.

Sodium Bicarbonate Thermal Decomposition Na 2 CO 3 60% NaHCO 3 40% 2.00 g 0.80 g 0.76 g 1.56 g

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 CO 2 and H 2 O are produced? How many moles of NaHCO 3 have decomposed?