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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
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Percent composition: Percentage by mass of each element in a compound. What percent of gum is sweetener? Percent Composition
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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
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% 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
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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
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CuSO 4 5H 2 O v. CuSO 4
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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
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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
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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
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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
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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
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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
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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.
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