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February 28, 2014

February 28, 2014. Final Polyatomic Ion Quiz Due: HW 7B Percentage Composition Lab Report due Wednesday March 5 Today’s video: Oldest known piece of earth How old?! What do you think their “technique” is? Z irconium silicate -  ZrSiO 4. Percent Composition.

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February 28, 2014

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  1. February 28, 2014 • Final Polyatomic Ion Quiz • Due: HW 7B • Percentage Composition • Lab Report due Wednesday March 5 • Today’s video: Oldest known piece of earth • How old?! • What do you think their “technique” is? • Zirconiumsilicate - ZrSiO4

  2. Percent Composition • Percent composition: Percentage by mass of each element in a compound. • What percent of gum is sweetener?

  3. Percent Composition • Mass percentage of an element in a compound is the same regardless of the sample size. This is because the ratio of one element to another in a given compound is the same regardless of sample size. • H2O = 2 parts H : 1 part O

  4. To calculate % Composition • % element in compound = n(Molar mass of element) x 100 Molar mass of compound n = how many of that atom in the compound

  5. What are hydrates? • Ionic Compounds that include water in the crystal lattice • ZnSO47H2O • For every one formula unit of zinc sulfate, there are seven water molecules. • If heated, the water will leave

  6. CuSO45H2O v. CuSO4

  7. Example: Carbon dioxide • Find the percentage composition of: • Carbon dioxide, CO2 • Molar mass of CO2: 12.01 + 2(16.00) = 44.01 g/mol • % C: 12.01 g/mol x 100 = 27.29% C 44.01 g/mol • % O: 2(16.00 g/mol) x 100 = 72.71% O 44.01 g/mol Check by adding the %s: 27.29 + 72.71 = 100.00%

  8. Example: Sodium nitrate • Find the percentage composition of: • Sodium nitrate • Molar mass of NaNO3: 22.99 + 14.01 + 3(16.00) = 85.00 g/mol • % Na: 22.99 g/mol x 100 = 27.05% Na 85.00 g/mol • % N: 14.01 g/molx 100 = 16.48% N • 85.00 g/mol • % O: 3(16.00 g/mol) x 100 = 56.47% O 85.00 g/mol Check by adding the %s: 27.05 + 16.48 + 56.74 = 100.00%

  9. Practice: PbCl2 • Find the percentage composition of: • Lead (II) Chloride • Molar mass of PbCl2: 207.2 + 2(35.453) = 278.106 g/mol • % Pb: 207.2 g/mol x 100 = 74.50% Pb 278.106 g/mol • % Cl: 2(35.453 g/mol) x 100 = 25.50% Cl 278.106 g/mol Check by adding the %s: 74.50 + 25.50 = 100.00%

  10. Practice: Ba(ClO3)2 • Find the percentage composition of: • Barium chlorate • Molar mass of Ba(ClO3)2 : • 137.33 + 2(35.453) + 6(15.999) = 304.23 g/mol • % Ba: 137.33 g/mol x 100 = 45.14% Ba 304.23 g/mol • % Cl: 2(35.453 g/mol) x 100 = 23.31% Cl 304.23 g/mol • % O: 6(15.999 g/mol) x 100 = 31.55% O 304.23 g/mol Check by adding the %s: 47.14 + 23.31 + 31.55 = 100.00%

  11. Practice: CH4 • Find the percentage composition of hydrogen in methane • Molar mass of CH4 • 12.011 + 4(1.0079) = 16.0426 g/mol • % H: 4(1.0079) g/mol x 100 = 25.13 % H 16.0426 g/mol

  12. Practice: ZnSO47H2O • Find the percentage composition of water in zinc sulfate heptahydrate. • Molar mass of ZnSO47H2O • 65.39 + 32.066 + 4(15.999) + 14(1.0079) + 7(15.999) = 287.561 g/mol • % H2O: 14(1.0079) + 7(15.999) g/molx 100 287.561 g/mol = 43.85 % H2O

  13. Wait - What are hydrates? • Ionic compounds that include water in the crystal lattice. • ZnSO47H2O • For every one formula unit of zinc sulfate, there are seven water molecules. • The dot indicates ratio, not “multiply” • If heated, the water will leave the compound and the color will change.

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