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

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

3. 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. H 2 O = 2 parts H : 1 part O Percent Composition

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

5. What are hydrates?  Ionic Compounds that include water in the crystal lattice  ZnSO 4  7H 2 O  For every one formula unit of zinc sulfate, there are seven water molecules.  If heated, the water will leave

6. CuSO 4  5H 2 O v. CuSO 4

7. Find the percentage composition of: Carbon dioxide, CO 2 – Molar mass of CO 2 : 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% Example: Carbon dioxide

8. Find the percentage composition of: Sodium nitrate – Molar mass of NaNO 3 : 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/mol x 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% Example: Sodium nitrate

9. Find the percentage composition of: Lead (II) Chloride – Molar mass of PbCl 2 : 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% Practice: PbCl 2

10. Find the percentage composition of: Barium chlorate – Molar mass of Ba(ClO 3 ) 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% Practice: Ba(ClO 3 ) 2

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

12. Find the percentage composition of water in zinc sulfate heptahydrate. – Molar mass of ZnSO 4  7H 2 O – 65.39 + 32.066 + 4(15.999) + 14(1.0079) + 7(15.999) = 287.561 g/mol – % H 2 O: 14(1.0079) + 7(15.999) g/mol x 100 287.561 g/mol = 43.85 % H 2 O Practice: ZnSO 4  7H 2 O

13. Wait - What are hydrates?  Ionic compounds that include water in the crystal lattice.  ZnSO 4  7H 2 O  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.